Welcome to our resource for MG Car Information.
MG MGA - More on Vapour Lock
|My 1500 Coupe vapour locked twice this Sunday, on arrival at Silverstone (Had to be pushed the final 100 meters) and halfway back home at a road junction. Its never done it before despite running on the hot side when pushed hard. I have driven hard over Spanish Cols and despite having temperatures almost off the clock it has never showed any tendency to do this before. So what has changed other than the day was hot but not unreasonably so? I think I know the answer. The car is fitted with an 'on the front' of the rad Kenlowe which is fine in the UK winter but not that good in the summer so as usual I had reinstalled the engine fan to supplement cooling. A week or so ago I set the Kenlowe to cut in earlier which I think was my mistake. The fan is very efficiently pushing very hot air into the engine compartment too early with little or no extraction and cooking the carbs. (The car has the correct heat shield and blocks fitted). Interestingly another A pulled over to help and said that he had problems after fitting a Kenlowe and took it off in the end. Now I am not saying that the Kenlowe installation is bad because there must be thousands out there that work well just that the cut in figure of the fan is more critical with high ambient temperatures. Am I barking up the wrong tree?|
|D J ROUGET|
|I too had 2 occassions on Sunday of vapour lock. The engine did not stop but on both occassions the engine stuttered rather worryingly.|
I have only had this occur a couple of times before when I was in France a number of years ago. On those occassions the temperatures were so high many people died in France due to the heat.
I am convinced the ambient temperature on Sunday was very high and was a severe test. The temperature of the engine did not go above 190 but I had vapour lock following a very slow moving horse box and also a slow moving lorry.
When I reached the A1 and was able to travel without blockage the car ran flawlessly.
I have a fuel pump under the bonnet and am wondering whether to move it to the rear axle.
|Robert (Bob) Midget Turbo|
|Modern fuel with 10% alcohol content is particularly susceptible to boiling when the carbs are hot i stop and stop traffic conditions. When it starts to boil, vapor bubbles in the main jets cause it to run lean. The immediate solution is to pull the choke to enrich the mixture, same as you would do for a cold start. Once you get moving again in free air the carbs cool down and the problem goes away.|
I think a long tern solution requires a better heat shield. I have done this recently, and it appears to help some, although it hasn't had the ultimate workout in killer heat yet. See here:
|I had the same problem a few weeks back - see thread. I since noticed an interesting article (letter in fact) in the current practical classics mag; the one with the MGA on the front - page 30 if you want a quick sneaky look in Smiths!|
The contributor says that he cured the vapour problem from ethanol by fitting an electric fan and having the manifold coated. But he said that whilst that cured the summer over-heating he then discovered a similar problem in the winter! He suggests this is due to the fuel being made more volatile in winter to assist cold starting. He adds that he believes BP Ultimate is ethanol free.
Interesting but cannot vouch for the accuracy.
|Graham M V|
|I have only experienced vapour lock on the one occasion when a couple of years ago I first took my car through the centre of Sheffield on a hot summer day in heavy traffic.|
It started to misfire, would not tickover and really struggled to restart after cutting out at some busy traffic lights.
My car even got a mention on Radio Sheffield that day but only because it was blocking a busy junction!
Once back on open roads the car went back down to 185 degrees .
I believe that it was a combination of a tight engine not yet fully run in and the fact that both of the front air intake hoses had not been securely fixed and had fallen into the radiator duct and were blocking the airflow through the radiator.
Once I had properly secured them I have never suffered vapour lock again.
I have a tuned MGB engine fitted but even with the standard metal fan it has never gotten much hotter than 190 degrees even on a long incline on a hot day.
The only obvious mods are the twin cam type louvred panels in the inner wings and a double row of louvres in the bonnet which allows excess heat to escape at lower road speeds.
So I think that maybe the louvres could be just tipping the balance on a car with a marginal cooling system and using modern fuels.
Has anyone else with a louvred bonnet noticed a reduction in running temperature?
|I intended mention the fact that the larger diameter injection moulded plastic fan I now fitted has reduced the running temp by 10 degrees but is much noisier.|
(Sorry for bringing this up again)
|I don't think there are any problems with the engine itself running hot, but the carbs do seem to suffer when the engine is hot AND the car stopped or moving very slowly. It gets mighty hot under that bonnet under those conditions, even the bonnet stay on my car is almost too hot to touch! As far as I see it, the problem lies with getting that hot air out of there, the fan justs keeps adding more and more heated air to the problem. I think Colyns louvres are one solution, but I have had an idea that wouldn't involve cutting any bodywork. What about a fan fitted inside the fresh air duct to the carbs? This could be either switched on when needed (via the good old 'F' switch on the dash) or controlled by a thermostat in the same way as the MGFs engine compartment fan. This would draw in fresh cool air from in front of the rad and pour it directly over the carbs, it might even help to push some of the hot air out of the engine compartment. What do you think?|
I was the driver of the car that pulled over to help last Sunday.
I do have a Kenlowe fan still fitted to my car and I have removed the meachanical fan.
Before fitting it I had terrible problems with overheating in slow traffic and hot conditions, the temperature gauge would go off the scale unless I pulled over, but I never encountered vapour lock.
Last year at Classic Le Man I was caught in an enormous traffic jam through Arnage in incredibly hot weather. The engine did not overheat at all with the Kenlowe but I did get vapour lock a couple of times.
My assumption has been that the electric fan keeps the engine temperature down by improving cooling of the rad but does little for the engine bay temperature. Consequently when previously I would have been stopped for an overheated engine I continue and the engine bay just gets hotter leading to vapour lock.
I fitted a heat shield to try to improve things and have had no problem so far (or on Sunday) but I am considering a computer case fan to either blow or suck around the carbs as Lindsay suggests.
|I was at Silverstone on the Saturday and drove the 120 miles back home on hot Sunday. Totally standard configuration on my car (Bob West original spec rad). The temp was 185 all weekend, just creeping up to 190 in the traffic queue into the event.|
That said, when I got home the car would not restart and flooded. I waited 10 mins. It then fired. The RPM hunted for about 20 seconds then settled down.
I have been running 95 RON for the last 2 fill ups on cost grounds. I do not normally have this sort of issue when I put 98 RON (super unleaded) in the tank. Does the higher octane fuel have the same alcohol ratio that Barney talks about?
|Steve, just what do you guys in the UK consider to be "hot"? (I'm referring to ambient air temperatures by the way, not engine/coolant temperatures).|
|Steve, that sounds very familiar and probably happens to most MGAs if they have been well warmed up then sit for while with the engine stopped. Come back after a couple of hours and the engine will start normally, but try to start it after a few minutes and it will do what you describe. The heat just sits there and cooks everything including the carbs and the petrol in them. I guess opening the bonnet for 5 minutes before starting would solve the problem.|
Not as hot as you get. Trouble here is often the high traffic volume causing plenty of slow running and high heat soak. Sunday was about 33 in the shade.
No need to go abroad for the sun tan this year. Burnt to cinder after the driving and watching all the racing - and yes, I had the high factor cream on.
|That's right Steve. 33C is certainly starting to get warm, though. We'll see high 30's quite often, even 40 or 42 on the occasional day around my parts. I wouldn't personally go out in my MGA over 38 or so; it's simply too uncomfortable.|
Funnily however these sorts of temperatures (35-40) don't seem to bother my mechanically similar (and bog standard) MGB at all; no shroud, and just the standard mechanical fan. I can only presume the much more spacious engine bay of the MGB allows less heat trapping/heat soak and better air flow-through with respect to the radiator, avoiding the fuel vaporisation and hot running issues we see with the MGA.
|It is interesting that Morgan sportscar has a similar narrow and tall engine bay shape to the MGA but it is heavily louvered on the sides and top to allow hot air to escape. As you say Tom, the MGB is more spacious being wider than it is tall so it doesn't trap so much hot air and doesn't have the same problem as the A.|
|Here is an article I found from google. Lindsay, he seems to think your computer fan idea works.|
Apologies if it is not a proper hyperlink but not sure how to do that
|Thanks for that Graham, very interesting. I've been trying to find a suitable round 12 volt fan to fit inside the duct but nothing yet.|
|Lindsay, this 4" bilge blower might work:|
|Thanks Chuck, someone else had pointed me in that direction and I have managed to locate one over here and have got it ordered. http://tinyurl.com/5wjambu|
|Lindsay, Merlin Motorsport sell a 3" in-line blower fan,|
|It will be interesting to see if they work. At speed air blows in through those vents. Putting a blower in will be attempting to counteract the airflow. Will it beat it or will the airflow just stagnate?|
|Steve, do you mean the 'MGA' vents? The fan would only be needed when stationary or at very low speed. I don't think anyone is getting vapour lock at normal road speeds. A manual switch for the fan is probably the best way to go.|
|Lindsay, I would have thought that the most improvement would be gained by venting a greater volume of hot air out of the engine compartment, rather than forcing more cool air in.|
A couple of computer cooling fans in the "MGA" shroud vents may help in traffic but I would have thought that a larger vent or vents somewhere out of the inner front wings may be a more effective solution.
I cant see any way of doing this without a bit of bodywork modification though.
Thanks for all your comments. Clearly coolant temperature is not necessarily linked to the temperature in the engine bay. Also pulling the choke didn't seem to work. I have my doubts that a fan in the intake duct will work but would love to be disproved. No doubt some fuel specifications are better than others, I guess you pay for what you get and the higher RON might just make the difference. Extracting the air via bonnet louvres would undoubtably help and something I will consider. To G Derham from Witney apologies if I mis-quoted you with regard to the Kenlowe installation. Thanks for stopping anyway, interestingly at least half a dozen people offered assistance.
|D J ROUGET|
|If you push more cool air in something has got to get out of the way. The bilge fan (a bit more powerful than a couple of computer fans at 230 CFM!) is a simple and cheap solution so I will try that first. That duct to the carbs is there to feed them with cool air, I'm just going to make it do that when I'm not moving; which is becoming a more common occurence these days (A14 closed again today!).|
|that is some fan Lindsay!|
You should consider putting one in the fresh air trunking to the heater too.
You could use it to either get a real blast of cool fresh air into the car in the summer or if you turn the heater on you could perhaps use it as a hair dryer or to grill the odd burger or two on the windscreen air vents!
A really interesting idea though, will you let us know how it goes.
Very interesting. Please keep us posted on how you get on. I guess the biggest problem in the experiment will be waiting for another hot spell to test it!
An MGA owner I met today said that the felt "seal" fitted to the underneath of the bonnet is the answer. I dont have this on mine and so was easy pickings for him! Just wondering if anyone with it fitted still has the problem?
|Graham M V|
|There is some stuff about that felt seal on Barneys site. It is there to stop air from by-passing the rad core by going over the top. But if all the air entering the engine bay has come through the radiator it will all be hot air and add to the vapour lock problem!|
Yes, I was talking about the MGA vents - sorry; just re-read your earlier post.
I mentioned a year or so back that one way to release engine compartment pressure and temperature is to remove the gearbox oil filler bung. The hot air absolutely blasts out into the cockpit and engine temperature drops by about 5 degrees. Now if you could funnel that away you would be on to a winner. Instead of that hole, perhaps a hole in an adjacent area of the firewall panel with an attached pipe to duct it away underneath, perhaps over an inverted aerofoil section to improve down force as in F1! You could even mount your fan in that pipe.
|Steve, the heat certainly does travel down the transmission tunnel. Before I fitted the heater, we used to get quite a bit of warmth from the gear lever tower area, but that only happens when the car is on the move. Vapour lock is only an issue when stationary or moving slowly. Hopefully my forced cold air intake will cool the carbs and at the same time push the hot air out by displacement, we will see! No problems at all while I am on the move.|
|Hi Chaps, I too suffered a dose last week end of what I am sure was vapour lock when held up for twenty minutes in stop start traffic after coming off the motorway.|
Engine temp according to the gauge was not high ( 190 to 200). I wonder whether this is linked to particular brands of petrol. I am currently using BP Ultimate but also I'm using the Castrol Valvemaster Plus. Could this be contributing to the vapour locking ?
|D C Grahame|
|It's got to be something to do with this stuff we have to run on now. I'm sure MGAs haven't always given up the ghost when held up intraffic or run as hot as they do now.|
My duct fan is now ready for despatch and I will fit it as soon as I get it. I'll then be looking for a hot day to get stuck in traffic so that I can see if it works!
|Having owned and driven MGA's for nearly 40 years (in Australian weather!) I find that getting the radiators rodded out every, say, five years completely overcomes the problem.|
|Here is the heat sheild we built to overcome the vapour lock on the sunny Gold Coast. Its a similar material to what Barney used and is a ceramic material snadwiched between two layers of aluminium. We massivly increased the size of the sheild to "nominally" create a cold air box. There are additioanl layers of the material on the rear of the sheild aswell. The front edge is turned outwards so the hot radiator air blows behind it and the cool air from the side pipe is dumped there. It works well and the fuel bowls are quite cool to touch after a drive.|
The only down side is it limits access to work on the carbs or exhaust. I had to cut a 9/16 spanner down so i could tighten the carb bolts. Other than that i love it.
|Further to the comments above, We also have a radiator shroud which I believe is a big step to remove heat from the radiator as well as the engine bay. A shroud doesnt allow air to re-circulate aound the fan blade therefore forcing the air out of the engine bay.|
Oh, we also have a engine tray under the front of the engine bay back to the front cross member to help the cooling.
|There seems to be 2 problems being discussed here at the same time and IMO are 2 totally different issues.|
Engine overheating is not vapour lock, and as described above engine overheating can be cured by a good radiator.
Vapour lock is a different problem and it seems a number of us had this occur on Sunday without our engines overheating!
I blamed it on having my fuel pump mounted under the bonnet although with all the other people commenting on vapour lock on Sunday I am beginning to think that was not the cause!
David G not sure you caused yours with fuel as I use the cheapest possible 95 octane and I was suffering a bit of lock!
|Bob Turbo Midget England|
|Hi Bob, I think you are quite right about there being two different problems here although linked by a common factor i.e. hot weather.|
For my own question I was wondering whether in fact I was making the problem worse by trying to do the best for the old car with BP Ultimate (£1.49 a litre !!!) and the Valvemaster Plus and that the combination might in some way have made the situation worse.
|D C Grahame|
|Well, I have got my fresh air duct fan fitted and it blows a gale into the engine compartment! The draught can be felt right back at the left hand firewall, and when I close the bonnet, air can be felt escaping at both vents but more so at the left hand vent. The fan is quite noisy but if it keeps the engine sweet when I am in a hot jam I will be happy with that. I have wired it to the fog light swith so that I can run it when I need it.
|Go drive slow in hot weather and let us know if it really works! I have an empty Foglight switch right now, so thinking this is a great idea!|
JIM in NH
That looks really cool, if you excuse the pun. I can't quite tell from the pic, is it exactly the right size to fit straight into the existing vent tube?
We now need you to sit in some long traffic jams in intensive heat for the benefit of science!
What i also like about the "Sampford Carb Cooler" is that, I assume it is hardly visible once the grill is replaced.
|Graham M V|
|Lindsay, I'd call that a KMart supercharger!|
|Graham, I had to strip the paper lining from the inside of the duct for about an inch to get it to fit. There is no 'give' in the standard paper/foil ducting, so it wont stretch over the fan body. The fan body has a diameter of 4".|
If we get some hot weather, the best kind of test will be to give the car a good hard run and then let it stand until it starts to play up. I'll then turn the fan on and see if it sorts it out. All I had to do to fit it was cut the ducting back a bit. I used the existing hole for the duct clamp to mount the fan, so if it doesn't help all it has cost me is £24 for the fan and postage plus the price of a new air duct.
It would be interesting to tie some cotton threads to the MGA cowls. Someone on this BBS did an experiment a few years back. Stationary they stood up and at speed they were sucked inside. With your blower it would be interesting to see if they stand up when at speed and blower going. i.e. reversing the normal aerodynamic airflow.
|Not a really hot day today, only 23C, so couldn't get the kind of vapour lock that would stop the engine, but I have never had that anyway. Here's what I have found. The car had a good run of 12 miles each way with a break of about 1 1/2 hours in the middle. When I got home, I left the car idling, OK at first but after 5 minutes it started to run lumpy and the tick-over dropped from 850 to 700 with regular drops down to just over 500. I left it like this for a few more minutes but it got no worse, probably not a hot enough day. Anyway, I then turned on the fan in the carb cooling duct and after a few seconds the revs picked up, until after a minute or so the revs were up to an almost constant 850 and sounding good again. I then switched the fan off, and after a few seconds the revs started to drop and get lumpy again, getting back to the running conditions before I turned the fan on. I repeated this exercise several times and got the same result. So it appears that under todays conditions, the carb cooling fan will keep the engine ticking over sweetly indefintely.|
|I was speaking with a Triumph Stag (3L V8) owner this afternoon. Vapour lock is an epidemic in the British classic car fraternity at the moment. We are not alone with our MGs.|
|Well that's nice to know Steve! It's got to be this modern fuel don't you think? Would fuel injection be the answer, no float bowls for the fuel to boil in and a cold air feed for the intake. I'll see if my bilge fan works first!|
|Sounds like positive results on the first trial. The Sampford Carb Cooler looks like it could be the answer! Well done - and please keep us posted|
|Graham M V|
|Sounds great Landsay! Keep us informed as your test progress.|
|Be sure to do a write up for Barney! These fans can be had in the US for about $18 to $30 on Amazon.com, so it's a cheap and reversible mod.|
JIM in NH
|I've been on this issue for some time, even since the 4-inch bilge blower was recommended (by John Twist) as a cockpit ventilation supplement. See here:|
One characteristic of the vane-axial blower is that it makes more noise than a radial vane (squirrel cage) blower. A large fan at low speed can move a moderate volume of air at low pressure (free air). That's what a computer muffin fan does. A smaller fan at higher speed can move a moderate volume of air at somewhat higher pressure, up to 1-inch water column (about 0.05 psi maximum pressure differential). This is what the bilge blower does. This higher pressure is not necessarily needed for carburetor cooling, but it will definitely guarantee positive air flow against any light pressure that may be in the engine bay. A squirrel cage blower can move a moderate amount of air at higher pressure yet, possibly up to 2" water column (about 0.1 psi). This is better for pushing air through ducting, which is why it is commonly used for automotive and home ventilation.
The squirrel cage blower is used in the MG heater box. The common complaint with these is only that it does not blow enough air. A slightly larger blower with slightly stronger motor could move substantially more air with only a small difference in cost (BTDT). The factory choice for MGA was based on light weight and low cost for a production sports car, a typical compromise for a specific application. Other cars (especially larger cars) may have larger blowers as standard issue. The 4" bilge blower is a cheap aftermarket device to supplement air flow for MG ventilation, except the noise may be objectionable.
If you put an MGA heater blower up front it would likely move plenty of air to cool the carburetors, and run much quieter in the process. The big Healey (and maybe the Sprite) use a stand alone squirrel cage blower in a snail chamber to supply ventilation air. That blower is substantially large with the housing. The MGC uses a similar squirrel cage blower in snail chamber specifically for carburetor cooling. I haven't actually considered if it would fit in space allowed in the MGA.
If you don't mind the noise of the bilge blower, I would like to see someone install a 3-inch model, cut off the legs, and put it inside of the 4-inch steel tube along side of the radiator to blow directly on the carburetors. Out of site, out of mind, easy to service (if ever needed), and not taking up service space. I rather expect that you could switch a resistor in series with it to slow it down some to run quieter, and it would still blow enough air to cool the carbs.
So far I'm still in the improved heat shield mode, not convinced yet that the blower is necessary. I also have a different devious scheme for cooling the fuel so the fuel cools the carburetors with no extra electrical device needed, but that's a different story.
|Barney, I am wondering whether the improvement in the tick-over that the duct fan gives is due to the carbs breathing in cooler air. The improvement is almost immediate, which would surely not be the case if the petrol in the float chambers had to be cooled down. When it runs rough it sounds like it is not getting enough air (rich), is this due to the extremely hot air under the bonnet delivering less oxygen than is required for correct combustion? I think the jury is still out on whether the fan can stop real vapour lock, still waiting for a very hot day!|
|It can only run rough when lean if there are vapor bubbles in the main jet. Cool the throttle body down a few degrees and any vapor bubbles in the main jet will condense back to liquid fuel, and good running is restored. Cool air can do wonders to cool down a hot carb in short order.|
The model radio control aircraft people have some very good ducted fan engines, with loads of thrust due to good fan blade technology.
Here is just one example: http://tinyurl.com/5rb6k93
This example would sit comfortably inside the ducting. There are others with close to our 4" trunking diameter.
It takes 28 amps continuous current so you better up your dynamo/alternator.
|You would need another cooling fan to cool the cooling fan motor!|
|I am "warming" towards this technique and after listening to all opinions it sounds to me like a good solution to overheating carbs.|
I have seen something similar before with a T Type owner many years ago having a small fan blowing at his carbs, he believed it did the job so must have some merit.
I think I will have a go too.
|Robert (Bob) Midget Turbo|
|In 1986-1988 I had a Renault 5 GT Turbo as a company car (great fun). It too had serious vapour lock problems (just would not start when it was hot and had been sitting for a few minutes) and the fix was a small fan blowing cool air at the carb. It worked great, and was on a thermostatic switch that meant the whole thing was automatic.|
It was the only electrical thing that was reliable on the whole car - great fun to drive but absolutely not built for 30k miles a year
It seems to me that ever since you fitted your fan, our weather has been awful. Please do us all a favour and remove it so we can have our summer back!
|Graham M V|
the special offer fans are sold out :(
This is getting beyond a joke! For the sake of all of us with Roadsters, and the entire British Tourist industry, please take that fan out and let us have our summer back!
|Graham M V|
|Hang on a minute Graham, I'll just turn it off...............................there, is that better?|
|Phew that was a good read! My "A" does everything exactly the same as you guys describe.|
Barney mentioned 10% ethanol he uses in the states. The maximum allowed here in the UK until 2013 is 5%. I checked on Shell's V-Power and this does have 5%. I'm sure a lot of our fuels use ethanol now and I'm convinced this has made our "A's" more liable to getting vapour lock.
Steve mentioned the air flow through the bonnet louvres being drawn in at speed. Interestingly, in standard configuration, the rear carb runs cooler that the front one as it gets blasted with cool air from above!
I think we now need to find the ideal little fan for the job which can be switched on in a jam with minimal power.
Good thread chaps.
|P N Tipping|
|My little fan (see my 1st July posting) works Pete. Sounds a bit like an electric lawnmower but it keeps the engine sweet when the car is stationary or when re-starting with 230 on the gauge. I have used the 'F' switch to turn it on and off and only need it when in a jam.|
Very useful that 'F' switch. I used it for windscreen Fluid before fitting the Fog lights. So currently we have:
When I converted to Fog lights I tried using the double pull light switch in the W position. First pull put the wipers on; second twist and pull put on the washers. It did not work very well. I think it was a dodgy switch.
I wonder what alternative purposes some of the other lesser used switches could satisfy?
You could use that "F" switch for fuel.
Wire the fuel pump current through there as an anti-theft device.
|M F Anderson|
|Lindsay - that little fan sure looks like it works OK. Could probably blow you out of bed too by the look of it! Stay with it if it works and thanks for proving the theory. Slight overkill perhaps?|
I've been having a look, not successfully yet, at some of these very cheap (old MG habit) 12v DC computer and cooling fans.
I reckon cool air just needs to actually flow in as against nothing at all when we stop. A gentle low power fan will use less power too which is important for us dynamo lovers...
|P N Tipping|
|Pete, just been doing some rush-hour jamming through Cambridge this evening and used the duct fan about four times while sat in queues. Water temperature was just below 212 most of the time and the radiator fan was running. The engine was ticking over perfectly with absolutely clean throttle response. I didn't try without the duct fan to see if I got vapour lock, but I have had problems under similar circumstances in the past. I wouldn't think a computer fan could deliver enough air but I suppose it's worth a try, I'll leave that for someone else!|
It's not likely that the duct fan would be needed whilst the headlamps, wipers or heater motor were switched on, so a properly functioning dynamo and a good battery set should be able to cope with the 4amps drawn by the fan with no problems.
AS an aside, I had problems with my charging set for some time. I did test discharges on the batteries and found them to be OK. I checked the voltage with the engine at fast tickover and that too looked OK. After about 18 months of poor starting performance, I decided to have a close look at the dynamo and found that one of the brush springs had broken and fallen off, the only thing holding the brush in contact with the commutator was gravity! How the thing worked at all I don't know, but it did, except that it couldn't quite keep up.
|Running with the standard SUs instead of the Judson at the moment, so I am interested in this discussion. With the SUs I also have hot problems in traffic, which I don't at all have with the Judson in place.|
Lindsay, have you thought of spraying the fan assembly black to make it a little less conspicuousbehind the grille (I have a mesh grill so I may be oversensitive to this issue)
I know that even a small fan can help a lot from my Renault days, (there was no room for a bilge blower under the hood on that,) so Steve may be able to be a real cheapskate and come up with a solution under 25 pounds, perhaps the new pad is costing him too much!
|Dominic, I did think about spraying it but couldn't be bothered until I knew whether it would be useful or not. It doesn't really show behind the standard grille but I may spray it over winter. I suppose the Holley carb might be less susceptable to vapour lock or in a cooler spot than the SUs.|
|I have a second MGA heat shield. I'm wondering how effective it would be to sandwich it back to back with it's asbestos pads facing outward. The pads would be facing the fuel bowls and the two shield butt up to one another.. It would double both the shields and pads while using a minimum of space.|
Has anyone tried this?
|On second thought, the shields have just enough curve in them to prevent a smooth clean surface match.|
|A few of us have doubled up insulation on the original heat shield, even enlarged the perimeter some. It helps a little while driving, but is not a cure all. The carbs will still suffer after a hot shut down when the engine bay gets hot all through with no air circulation. Hard to combat that when the carbs are sitting right next to the exhaust manifold (like a Dutch Oven).|
|All the heat shields in the world are not going to help when the engine is shut down. The problem at that point is heat soak and heat shields are of little use in that situation. Heat shields only help as long as there air flow through the engine compartment. We have been experiencing the same problem over in the T series community and I have been watching this thread with great interest hoping to pick up some useful information, which I have in the success with the ventilation blower. I am going to try using a small computer fan that will move a bit of air through the engine compartment when the car is stopped since I am experiencing the same problem here in the cool Puget Sound region of Washington state.|
I think that something that is adding to the problem that we are all suffering is today's fuel formulation. It used to be that fuels had distinct formulations for winter and summer and a good hot day in early spring while still running winter grade fuel would cause vapor lock and heat soak problems. While I don't know for a fact, I would guess that there is no longer a winter and summer formulation since all modern cars are using fuel injection. With fuel injection, there is no concern about vapor lock as the fuel is delivered under high pressure (much higher than the high pressure SU pumps even thought of), so there is little danger of vapor lock. Even heat soak would not be so much of a problem with the pressures used for fuel delivery today. Also, most (if not all) of today's cars use electric fans that will run even with the ignition shut off if the engine compartment temperature rises above a certain point. Cheers - Dave
|After discussing this issue with a few MGA owners we question if vapor lock can be blamed on todayís fuels vs. formulas of the past. If that were the case it would be a big universal problem in the states and a subject of much hand wringing. It isnít.|
Iíll admit I recently experienced the issues mentioned during our 90+ degree weather. Runs sweet on the road and poorly in slow traffic crawl. On one occasion it stalled completely and would not restart until a half-hour rest. Caused yet to be determined.
I was reminded that Iíd put two things on my car that were part of the original design. However, they might not work as well as one might think. I installed the vent hose that goes from the grill to the carbs. And I had installed the pad that attaches to the bonnet above the radiator.
A friend suggested those two items may hinder the circulation of air into the entire engine bay and thereby cause greater heat buildup. Hum, come to think of it, I never had those items on the MGA I drove for 32 yearsÖÖ.. and I didnít experience the issue.
Yesterday I removed both items before going on a club drive to a brew pub a couple hours away. No issues yesterday. Itís too early to say the problem is cured but I thought Iíd toss my reasoning into the discussion.
|Has anyone been purchasing alcohol free gas. Go to this website |
My MGA was off the road for two years. Engine mods and transmission repair. Towards the end of this time out for me most of the higher percentage alcohol gas was first introduced. First hot summer day road test with everything newly back together and a fresh tank of gas, I was really excited experiencing the performance of the new extra horsepower. Coming to a line of cars at a train crossing, all were stopped, waiting for a slow train to pass. I shut off the motor and then tried to restart it about 10 minutes later -nothing. I had to push the MGA to a shady spot and wondered what was wrong, most likely some detail overlooked when everything went back together or a result of some original part sitting unused for several years. Reluctantly I called my very recently divorced ex to bring my tool bag. When arriving she shoved the bag at me and jealously eyed the MGA making a derogatory remark about my relationship with the car. By now about 45 minutes had passed, the ex drives away and I give it one more try – the car started right up. I got it into my head that it was a spark failure, I swear I wouldn't see a spark when this stall occurred, but I never could locate the cause replacing all ignition parts including the Petronix module. No problem at all after the hot summer ended and then the problem recently started happening again this summer. Since I switched to the alcohol free gas over a month ago the stall problem hasn't returned. Maybe I've got a compound problem of both a phantom spark and vapor lock. Spooks begone and knock on wood. Any one out there with a chemical knowledge? Might someone formulate a gas additive to reduce the alcohol vaporization we're experiencing?. -Martin Straka
|Martin, -- From the western suburbs of Chicago (where I live), it takes two hours and half a tank of gas to drive round trip to the nearest alcohol free gas station. For most of California you may not be able to make the trip with a full tank of gas. For many large metropolitan areas in the USA all gas has 10% alcohol. So, would you have an alternate suggestion for the vast majority of MGA owners who do not have any access to alcohol free gas?|
|There's always the convenience (and the danger associated with it) of storing your gasoline in the 5 gal. gasoline spec. containers. I wouldn't store containers next to your MGA. Here in Louisiana its an annual practice for me an some neighbors at the start of hurricane season to stockpile gas incase we need it for our generators in the advent of a bad storm. One trip in a pickup truck to fill up the gas containers you've brought in the truck bed to an alcohol free gas station could give you a supply. I have the advantage of finding several of these stations within a short drive from where I live, so storing gas for my MGA isn't an issue. Perhaps because some major refineries are located here in the New Orleans / Baton Rouge area its easier to find the alcohol free gas.|
Any chemists out there? To restate my earlier question would it be possible with an additive to reduce the vaporization of gas blended with alcohol? -Martin Straka
|I'm not a chemist by profession, but I've had enough chemistry classes to know that ethanol alcohol boils at 79dC (172dF). There may be some other chemicals in fuel that will boil at even lower temperature. I see a '66 Mustang guy reporting fuel boiling in a glass filter immediately downstream of an engine mounted fuel pump at 140dF (pump housing temperature).|
It all depends on fuel formulation, as various blends of gasoline may boil at temperatures between 100dF to 400dF.
Boiling Points (dF):
Ethyl Alcohol 172
Gasoline 100 - 400
Isopropyl alcohol 181
Methyl Alcohol 149
|Not too far off topic: I just had to search youtube for boiling gasoline videos. I found this clip of a Ford 8N tractor tank just a boiling away like mad. In the tractor, the fuel tank sits above the exhaust manifold. I can just imagine looking into the MGA SU fuel bowls sitting above the exhaust manifold, and seeing this activity.|
|I rather thought that the 140dF number in my prior post was considerably too low, so I did a little lab experiment myself. I took an electric fry pan out onto the back deck to boil some water. I placed a half full glass of fresh gasohol in the pan and brought the water to a boil, while measuring temperature of the fuel in the glass. The double boiler method is kind of slow, but it finally go there after about 45 minutes. I was measuring fuel boiling temperature of 185dF. That strikes me as being "in the ballpark" for what I was expecting.|
I can tell you that there are certainly circumstances when the carburetor bodies get much hotter than that. Sometimes after a particularly vigorous autocross run, mostly full throttle 2nd gear for about a minute, I can open the bonnet and trickle a little water on the carbs. The dashpot on top may be too hot to touch for more than one second, but doesn't sizzle. The carb flange where it bolts to the manifold will sometimes sizzle, meaning it is considerably hotter then 212dF so it will boil water on contact.
I am going to toss my infrared thermometer in the door pocket. Next time it's hot enough under the bonnet to cause bad running I will measure temperature of a few things around the carbs and will report the results.
|This may be of some help. One of my attempts to bring down the carb temperature was to construct with flexible aluminum reflective insulation a heat deflector going from from the original metal heat deflector plate to the inner fender well. Please see the tree frame photo. The actual installation looks cleaner than it appears in the photos. The insulation is inexpensive and I purchased a roll at Lowes. It has held up well to the engine bay temperatures. It is shaped to fit exactly and to block the open air space under the carbs. I first made a cardboard template to determine the shape and to cut the insulation from this template. (Remember holes for your carb vent tubes.) Its not going to help any heat that is transfered through the intake manifold but does block a considerable amount of the radiant heat rising up from under the carb bowls. The insulation is aluminized on both sides with a captured air space in between. I used aluminum foil tape (not duct tape!) to attach it to the manifolds metal heat deflector plate and to the fender well. This type of tape sticks well but will release at a later date without damaging the surface its attached to. An extra advantage is that it also makes for a more enclosed fresh air flow to the carbs if your fresh air duct is attached in your MGA and it also catches any weeping gas from the carbs. -Martin Straka
This thread was discussed between 27/06/2011 and 10/08/2011
MG MGA index
This thread is from the archive. The Live MG MGA BBS is active now.