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MG Midget and Sprite Technical - engine bay temps and vapour lock (Science warning!
| LONG POST WARNING! ive seen many posts in the archives about vapour lock and high engine bay temperatures , and when i got my car initially i had chronic problems. However i cured it (mainly) by using exhaust wrap, vents at the side of my frogeye fibreglass bonnet and a big vent in the top of the bonnet. But the main thing to my mind was the radiator shroud i made to force the air through the radiator.With these mods the car changed from not being able to go more than a few km. to being able to run, at 70mph + for as long as you want. However, after a long drive yesterday i had to stop in a queue for about 3-4 minutes at a police check point (you get these a lot in Thailand...) during the wait i noticed that the petrol pump started ticking a lot , (always a bad sign) then when i set off again the engine coughed, the rev counter dropped momentarily, but after me giving it a good bootfull of right foot it picked up again and ran perfectly all the way home. So today, i attached my formula 1 telemetry kit and did the same drive again, but this time recording temperatures. see the graph below RED line = temp in front of the radiator, so the temp of the air as it comes through the grille before it goes through the radiator . BLUE line = carb temp GREEN line = temp above the battery (highest point and furthes back in engine bay. PURPLE line = coil temp. many interesting things to see here if you look carefully.. first circled area is where i set off from work, had some road works, then a wait at a level crossing, then slow traffic till i reached the main road. 2nd circled area is where i stopped for petrol.. look at how the temperatures of the carb , battery and coil rise with the engine switched off. 3rd circled area is when i had to stop at some traffic lights... again look at how sharply the temperatures rise...but the carb not as much as when stopped for petrol due to it still sucking cooling air through... Not sure if i'm asking anything here, i have a few ideas of things i want to try such as moving the coil so it sits in a place with more air movement, and getting a cool air pipe to the carb. Just thought people might find it interesting. During the test engine temp was steady at between 82 and 87 degrees... time for test approx 40 mins. test started with engine just started.. if you look at the red line bottom left you can see where the thermostat opens and the radiator begins to get hot. Notice the ambient temp (red line) it was damn hot today...  |
| Andy Phillips (frankenfrog) |
| if you look at the green and purple line in the ' car running at around 60mph' zones between the circled parts then you can see that the coil (purple) runs at around 5 degs higher than the air temp around it (its local ambient temp) (my coil is very close to my battery). This leads me to believe that my ignition system is actually working quite well and is well matched.. The fact that it is hot to the touch is down to its siteing in the engine bay. if you look at the purple and green lines again in the third circled area then the temperature become very similar as the engine idles at the traffic lights, the coil is under very little load so the rising temp begins to coincide with the ambient.... Tomorrow i'm going to reposition the coil and do this same run to see if i can reduce the temperature it sees. The cooler the coil is the better it will work and last longer... |
| Andy Phillips (frankenfrog) |
| a quick thought - if you have your electric cooling fan thermostatically controlled and also wired so that it operates even when the ignition switch is off then the cooling fan will cut in when the engine and engine bay normally warm up even more because the cooling system is static without the water pump going or cooling air from the car moving forward (I'm sure there's a shorter and better way of putting that but it's beyond me now) (and I bet you already have it wired that way) |
| Nigel Atkins |
| Ha ha, that is cool! Mount the coil on one of the chassis legs right down low. Cool air passing and an easy place to cable tie it to for a test? Would need to extend the wiring a wee bit I guess. Cold air feed for the carb? NACA duct bonnet scoop. That would upset the purists :-o Malcolm. |
| Malcolm Le Chevalier |
| Malcolm note Andy's title, the purists would be at a lose to know where to start being upset :) |
| Nigel Atkins |
| Nigel, yes already wired that way, i have a battery isolator switch (with a big red key) mounted on the firewall in front of the gearstick. i normally leave the fan running for a few minutes once the engine is switched off, then once i remove the big red key everything is completely isolated. Who are these 'purists' ? |
| Andy Phillips (frankenfrog) |
| That is interesting! But why does the temperature in front of the radiator change so much? If this is upstream of the rad I don't understand this. Is your fan turning the right way? ! |
| Guy W |
| its just the radiated heat from the radiator when the car is stationary, the probe dangles down in front of the radiator but behind the grill. When the cars moving of course the airflow directs all the heat away from the probe. |
| Andy Phillips (frankenfrog) |
| A formula 1 telemetry kit sounds cool. Where can I get one? |
| graeme jackson |
| Another thing i just noticed...if you look at the bottom left, when the engines just started and car beginning to move, the revs rise and more air is sucked through the carb before the engine has had time to transmit heat through the manifold. The temp of the carb (blue line) actually reduces by a few degrees before it starts to warm up... It takes till about point 150 (bottom scale) to recover to where it was before starting. the datalogger is set to take a reading every 2 secs, so 150 points is 2 1/2 mins. Not a problem for me of course, but on a cold winters morning... in the first 2 or so mins the carb will be colder than when you started the engine .... ( i know that's not automatically true... disclaimer... etc etc) its all logical when you think about it, but seeing it on a graph actually makes you think about it... edit... i suppose thats why you guys are running water heated inlet manifolds.... |
| Andy Phillips (frankenfrog) |
| Andy, a few minute will not be enough - I can be certain of this as my electric cooling fan starts after I've switched the engine off and runs on for a good while (many, many minutes) even in UK winter! give it a try, leave the battery isolator switch on or wire the cooling fan direct to the battery to bypass this switch and see how that bring the temperature down or more likely in your case reduces the increase |
| Nigel Atkins |
| An aside: Nigel, my fan is wired to run on after the engine is switched off, just controlled by the thermostat. Since the fan rarely comes on anyway, only when stuck in standing traffic, it doesn't often run on after turning the engine off anyway. When it does, it is only for maybe 60 to 90 seconds at most as that is all it takes to bring the temperature down. Sometimes the fan will switch on, after turning the engine off, even though it wasn't needed with the engine running. This must be due to residual heat transfer from the block, once the airflow from the moving car has stopped but it sometimes startles people standing nearby! Andy, Have you considered ducting air from the outside to the carbs? At those underbonnet temps I would think it would be affecting the fuel charge ratios significantly. |
| Guy W |
| that's interesting :) I've thought of putting a fan controller /temp monitor from a computer in the car, you'd get 4 temperatures but no data logging stuff. |
| Rob Armstrong |
| Guy, I've got the Revotec with adjustable thermoswith in top hose, it's the sole cooling fan, it seems to go well below the on temp to get to the off temp I wonder if the fan isn't quite big enough for my engine but it does control temperature just seems to take it's time I'll time it if I remember next time but it's more than 90 seconds I'm sure Andy, what size or number of rows is your oil cooler and where is it positioned, perhaps you could supply it with a small dedicated cooling fan |
| Nigel Atkins |
| Nigel, i left the battery switch on this morning and the fan ran for 3 minutes before i invervened,, The trouble is that without the engine running the water isnt being pumped around the system, so you are relying on a thermosyphon/convection to circulate the water around. After 3 minutes with the fan running i started the engine again to circulate the water and within a few moments the fan turned off. Depending upon the operating temperature points of your switch and your thermostat, you could find that the thermostat closes (or closes enough to stop the thermosyphon action) before your lower set point in your fan switch is reached. Then you have a stagnant pocket of water stuck in the top hose next to your fan switch which isnt actively being cooled. Once flow of water stops then an internal convection system will develop within the radiator and the fan will just be cooling that water, and not the engine and not the water next to the fan switch, so it (the fan) will run for a long time. You can get electric water pumps which have a programmable controller that can be used to keep the water flowing through the system for a set time after the engine is switched off. This seems like a good idea to me, but they are quite expensive. However, you got me thinking... and at 5am this morning i had an idea... When the car is stopped, that is the time when the electric fan comes on, but what it does is take heat from the radiator and pushes it into the engine bay, making the heat rise even worse than you would otherwise get. It forms a vicious circle where heat is extracted out of the engine, then is blown back at the engine again which recycles the heat. Now, if the car is stood still why not reverse the polarity of the fan to make it suck air out of the engine bay and push it forward, through the radiator and out of the front of the car. Of course this would be disastous if the car was moving, but a simple circuit could be wired up that involves a microswitch attached to the throttle linkage so that if the throttle is pressed then the fan sucks, but if not pressed then it blows. project for this weekend i think.... I dont have an oil cooler... this is what the datsun engine website says about them.. ******* The oil temperature is controlled by the engine coolant temperature. As long as the engine coolant ("water") does not overheat, neither will the oil. Only a very few high performance cars have a separate oil cooler. So this means: keep your coolant temp low, and your oil temp will be happy. Count on the oil temp to be about 20 F degrees hotter. So here is a good street performance equation: Thermostat: 180 F degrees Oil temp will run about 200 F degrees At this temperature, the good quality regular oil (inexpensive) will perform as good as the expensive synthetics in a street car. It is high temps that ruin regular oil whereas the synthetic oil can take high temps OK. Now if you are racing or towing there is more to talk about. ************ i have no problems with my engine temp, it runs very nicely at between 82 degs (where the thermostat opens) and 82 to 87 degrees (the start and stop points on my fan switch). i run Castrol GTX. |
| Andy Phillips (frankenfrog) |
| My F1 telemetry system .. otherwise known as a USB datalogger. its powered completely by the USB so you can just attach it to a laptop and put in the car.  |
| Andy Phillips (frankenfrog) |
| Hi Andy, yeap I know what you mean about the fan giving itself work when car is parked, surely that was ultra clear by my Prop like explanation :) during extensive and extended real world use (using the car and having fitted the fan kit a couple of years back :) ) I've been experimenting with the temp setting for the fan since I fitted it and have come to a compromise setting I've think I've observed (not recorded or confirmed), from the water temp gauge in my car, that the gauge reading at it's maximum after turning the engine off reads a little lower if the fan runs on than when it didn't so in the warmer weather I can return to the car and it not be a hot engine, in fact this car's engine temperature particularly seems to cool and get cold very quickly there's sometimes debate about the location of the thermoswith but I stuck with the suggested location of top hose if I had a remote control for the switch I'd set it at two different settings for moving and static but as it is I have a 'best set' once for 'winter' once for 'summer' compromise to save fiddling with it every journey and part journey I'm with you about oil coolers but thought you might have one if it's very hot out there, there are other advantages to those oils labelled synthetic but if your doing timely thorough changes with GTX then you're already on a good course |
| Nigel Atkins |
| Andy, Do fans not only move air in one direction whichever way they turn? i.e. they only suck or they only blow even when they turn clockwise or anti-clockwise. But they are designed to spin in one direction as this is the way in which the blades operate at their most efficient. So reversing the direction of the fan from sucking in to blowing out by spinning it backwards wouldnt work. It would still suck, just less so. Malcolm. |
| Malcolm Le Chevalier |
| Hi Malcolm. If you reverse a propeller direction, you reverse the boat. So too with air movement through a fan. You're right about it's design efficiency, but it will still shift the air in a reverse direction if you reverse it's spin. |
| Lawrence Slater |
| I wonder where I got that notion from then... Hmmm... Ho hum. I believe you! Malc. |
| Malcolm Le Chevalier |
| ok, new data from todays trip home... (pls tell me if this gets too much !!) this time i moved the sensor which was on the coil to be in the throat of the carb, inside the air filter. lets see if a cold air intake is worthwhile.... just to remind everyone.. RED line = temp in front of the radiator, so the temp of the air as it comes through the grille before it goes through the radiator . BLUE line = carb temp GREEN line = temp above the battery (highest point and furthes back in engine bay. PURPLE line = air charge temp in mouth of carb. 1st circled area is in traffic/roadworks. 2nd is stopping for petrol at the same garage as yesterday. 3rd is stopping at the traffic lights 4th is arriving at home and leaving the engine running for about 10 mins to see what happens, (during this time the fan cycled about 3 times which you can see by the sawtooth peaks on each trace..) at the red line i opened the bonnet and turned of the engine and just left it.. interesting thet the air charge temp is only 3 degs above the ambient air temp once under way, but climbs rapidly when car is stopped (as ypu would expect) This hot intake air will also heat up the carb, and you can see the close corrrelation of the air temp and carb temp (purple and blue lines.) Based on this evidence i would say that a cold air intake is not really worth it whilst the car is moving, but when the car is stopped then the cooler air from outside would help keep the carb cool which would help tremendously with the vapour lock issues. look at what happens to the carb and air charge temp when the car is stationary,... goes through the roof... but then once the bonnet is opened the air temp reduces straight away whilst the carb continiues to rise due to heat soak from the rest of the engine and the fact that its a physical aluminium thing rather than just an air measrement... so... cold air intakes ---GOOD, but not for the reason you would expect... please feel free to pull my reasoning apart......  |
| Andy Phillips (frankenfrog) |
| Any idea how many cfm of air the carbs draw at idle? |
| Trevor Jessie |
| Andy, My point wasn't about having an external air supply to keep the carb cool and prevent fuel in he lines vapourising. In your hot climate, the underbonnet temperature is going to climb and heat the carb when the car is stationary. But by drawing the air supply for the fuel mixture from outside the engine bay you would be using cooler, and more dense air. And the more dense air will hold more fuel vapour and give more power when ignited in the cylinders. Its a different benefit. |
| Guy W |
| Hi Guy, Yes, understood your point,The cold air intake is usually touted as having big performance benefits. and i think in modern turbocharged engines that is correct. and certainly cooler air is much better for power( as long as your carb is jetted correctly to match) i wanted to put some figures on this (as much as i am able considering my resources and my definite novice level experience) after all if you cant measure it you cant improve it... From the test results today it shows that while the car is moving the difference between the air charge temp and that of the air as it enters the car is only 3 degrees or so. Yet the under bonnet temp where measured above the battery is maybe 8 degrees higher. The reason for this difference is the position of the carb in the engine bay and also (and i need to test this theory) because the carb may be pulling air from outside already to a certain extent (see picture of the bonnet vent below, this is supposed to be venting hot air, but maybe the carb is also pulling cool air in through it) the best possible case you will get is where the air charge temp is the same as the outside ambient... Now i'm not sure of the performance benefits of a 3 degree reduction in charge temp when running, but i can see a definate advantage in terms of keeping the carb cool when the car is stopped. So to develop a cooler air supply system would have multiple benefits. Every ones a winner ! Hi Jessie, I dont know the answer to the question but maybe we can work it out? The carb is a Hitachi twin choke (similar to a weber DGAV) bore sizes of 26/30 and venturis of 20mm (primary) and 26mm (Secondary),My engine is a 1493cc nissan A14, idle at the moment is 1000 rpm (not yet tuned it). air filter is a paper type , just something i managed to get to fit from the motor factors |
| Andy Phillips (frankenfrog) |
| sorry picture now attached, you cant see it very clearly but the air filter is just behind the vent opening. The reason for that particular type of vent was that it would allow an extra 20mm or so of space to fit an air filter to the top of the downdraught carb. When i got the car is simply didnt have a filter as it wouldnt fit. This vent killed two birds with one stone..  |
| Andy Phillips (frankenfrog) |
| as you've put it depends on your carb set-up/tuning and again I've no figures but when it's cooler my carbs/engine seem to go better so I'd say a cold/cooler induction kit (ducting with possibly a filter) should be useful 'at work, rest and play' where you collect that air from should be interesting, new source or diverting existing supplies |
| Nigel Atkins |
| i think its always going to come down to , bonnet vents, cool air intake, sheilding, insulating etc, but its good to have some figures to work to. i'm quite pleased about the result for the coil temp as that shows (to my mind anyway) that i dont have an ignition system problem, whereas before i thought maybe i had. Before i change anything too drastically i think i'll do some tests with my current vents (one on top and one each side of the bonnet) just to see how effective these really are. keep tuning for more riveting facts and figures.... |
| Andy Phillips (frankenfrog) |
| Andy, I don't think we are disagreeing. But I do suspect we are really considering different situations. I suspect that your ambient temperatures are such that there is relatively less benefit in drawing air from the outside than I would benefit from on a cool autumn evening in the UK (when mine runs at its best!) Conversely, I have never had a problem of fuel vaporisation on my current 1275. Although my 1500 used to suffer very occasionally in "hot" UK summers! But from what I understand, this is your greater concern? |
| Guy W |
| OK Andy, So how do you get multiple sensors onto one data trace ?. I am a novice at these things (and quite old), so please explain slowly. I had had my 1275 midget since 1983. Thanks in anticipation Tony Australia |
| A L SLATTERY |
| Guy, yes, i think we are on the same wavelength, if i can get some extra power and have a better running engine by making a cold air intake then i'm all for it. And if at the same time it also reduces carb temp rise when the car is idling then thats all to the good as well.. My biggest worry is getting stuck in traffic then having vapour lock and having to push the car to the side of the road.... As theres only two of these cars in thailand it draws a lot of attention, i get at least 3 cars every day slowing down and driving next to me whilst people take videos and pictures. Seeing a foreigner with a strange old car broken down at the side of the road will draw major attention , and embarrassment for me..and , as you know, the car will always have a problem just at the worst possible moment.If i had to go into Bangkok, with its renowned bad traffic, the car would probably fail at a major junction and would probably make the news in the 'and now for something different' section at the end. plus, (if you havent noticed already!) i like playing around with these things... its nice, after a years worth of welding, angle grinding, engine stripping and cleaning, to be able to do something which lnvolves driving the car... |
| Andy Phillips (frankenfrog) |
| Hi Tony, my datalogger puts all the readings into a text file in the following format 34.5,33.6,38.0,40.1 33.0,33.7,39.6,41.0 34.0,33.8,39.0,41.2 there is a line every two seconds, so after my drive home i get 4000 ish lines of data. i import the data into excell using the DATA menu and 'import from text' option. Then you have to tell excell that the file is comma delimited, meaning that it is to use the commas to seperate the string of text into different cells on the spreadsheet. once the data is imported you end up with four columns of data . click on the top left hand corner of the data, then go to the bottom right hand of the data (use the scroll bar to do this as its quicker), click on the cell with the number in it whilst holding down the shift key. this then highlights all the data. now go to the 'insert' menu at the top and click on the picture of the graph with lines on it. Excell will do the rest and give you a graph straight away. once you have the graph you can right click on the axis scale etc to change and fine tune things... good luck.. i use this every day for my work and its very usefull and easy to use once you know what to do. |
| Andy Phillips (frankenfrog) |
| ok, todays figures... not gone to work today so did some tests static in the garage. first test. started engine and just let it tickover, fan operating normally via the temp switch. things to notice are the sawteeth in each trace showing where the fan cuts in and out. and the temperature of the carb and intake air charge temp. intake air gets up to 73 degs, carb gets to 65 degs.. general under bonnet tem gets to about 63 degs with the fan working normally the heat extracted from the radiator is forced into the engine bay, then sucked into to carb, recycling the heat over again. again, colours are: RED line = temp in front of the radiator, so the temp of the air as it comes through the grille before it goes through the radiator . BLUE line = carb temp GREEN line = temp above the battery (highest point and furthes back in engine bay. PURPLE line = air charge temp in mouth of carb.  |
| Andy Phillips (frankenfrog) |
| 2nd test, everything exactly the same but electric fan polarity changed, so that it pushes air out of the front of the car. definate difference in temperate with this mod... max temp reached by the air charge was 56 deg, max for the carb temp was 53 degs, max under bonnet temp about 56 degs... so significant temp reductions. Fan ran fine in the opposite direction, i timed it to be 40 seconds running, 40 seconds off, so still capable of cooling the engine, and the temp gauge behaved as normal. i think this is a good, cheap and simple mod..and i cant see any disadvantages.. please speak up if you can see any problems... i will devise a circuit, linked to the throttle linkage, that changes the polarity of the fan when the car is stopped, but leaves it as normal when the throttle is pressed. Should be quite easy and give me a big improvement for next to no outlay. With the previous test i was worried my bonnet might start to melt ! the red line in the graph shows the air temp in front of the radiator, thats why it looks so different in this graph compared to the others as its now measuring the air temp downwind of the heat exchange... towards the 2nd half of the test i switched the engine off, but left the fan connected. The fan ran for a good 3 minutes before it stopped, you can see the difference in the width of the sawteeth from LHS with engine running and RHS with it off, and so no coolant circulation.. next step is to have a go at making a cool air intake...  |
| Andy Phillips (frankenfrog) |
| Hi Andy, I have just read the thread with interest. As well as my frog, I have an MGA and that suffers very badly with vapour lock, altho sadly the ambient temperature is often not that high to cause it. I have installed a powerful pump (an in-line bilge pump) that blows fresh air at the carbs drawn from in front of rad. I only switch it on when I stop in traffic etc. Altho we haven't had the weather to test it properly, the idea came from others on the MGA forum, and the general opinion is it cuts down vapour lock dramatically, by reducing the temp of the carbs when near stationary. I am wondering if ethanol in modern petrol is also a contributing factor? Regards, Graham |
| Graham V |
| Hi Graham,.. yes good point... i looked up petrol boiling point on google and just got a flat 95 degrees. However, i'm running E20 (20% ethanol), so i'm sure the boiling point is less but not yet found the information....need to look harder... I had a look at the mgtf forum, they have issues with engine overheating which causes HGF. These cars had specific engine bay fans to pump hot air out of the engine bay when required. |
| Andy Phillips (frankenfrog) |
| Andy That's interesting. The boiling point is clearly going to be critical to vapour lock problems. 20% ethanol sounds high. I think, but not sure, that it is only 5% in the uk with plans for it to increase to 10% soon. But apparently Shell sell a petrol grade free of ethanol. I will find out which. Graham |
| g Victors |
| something i found from a study done in australia.. Carburettor Equipped Engines Vehicles made before 1986 vehicles were predominantly equipped with carburettors and steel fuel tanks. The use of ethanol blended petrol in engines impacts the air/fuel ratio because of the additional oxygen molecules within the ethanol's chemical structure. Vehicles with carburettor fuel systems may experience hot fuel handling concerns. This is because the vapour pressure of fuel with ethanol will be greater (if the base fuel is not chemically adjusted) and probability of vapour lock or hot restartability problems will be increased. As a solvent, ethanol attacks both the metallic and rubber based fuels lines, and other fuel system components. Ethanol also has an affinity to water that can result in corrosion of fuel tanks and fuel lines. Rust resulting from this corrosion can ultimately block the fuel supply renderingthe engine inoperable. Water in the fuel system can also result in the engine hesitating and running roughly. theres some other interesting stuff in there http://www.ahmf.org.au/PDF_Docs/Ethanol%20in%20Petrol%20final.pdf |
| Andy Phillips (frankenfrog) |
| Disclaimer, i'm nor a chemist/physics expert, just looking at stuff on the net and trying to understand it... so please dont take this as gospel, though it seems to make sense to me. from other studies i have found, there is something called RVP, basically its to do with the pressure that evaporated fuel will achieve before that self generated pressure stops any more from evaporating ... so it happens before the point of boiling... The std test for this seems to be done at 70 deg C.(a temp very achievable in the engine bay as i have shown in my tests) using ethanol mix in petrol increases the RVP. this means that given two identical containers, one with ethanol mix and one with just petrol at 70 degs then the pressure in the ethanol one would be greater. so if youve got ethanol in your carb float chamber and it gets hot, then the vapour pressure above the surface of the fuel will increase and push it down against the pressure in the fuel lines. Of course if this happens then it will make the engine run lean, or in extreme cases, stall, as the level of fuel in a carb flat chamber is critical. This effect is more pronounced in ethanol mixed fuel than in unmixed petrol. of course this has no effect in fuel injected engines as the fuel pressure is much higher, and the return pipe to the tank makes the fuel circulate so it dosent heat up as much anyway. Disclaimer again.....this is just my interpretation.. Maybe someone who knows what they are talking about could blow my theory apart....? |
| Andy Phillips (frankenfrog) |
| ETA: I typed this before the previous post so refers to last but one post (and on a skim read to beat edit guillotine, last post) on the link I couldn't see a date but reference was made to 2002, I realise physics doesn't change in 11 years (the understanding of it does change with time though) but the make up of petrols does change I do remember that some said the universe would fall in on us when lead-free petrol came in and that engines would be popping left right and centre, then others said you must use additives to prevent this will history repeat itself, we'll have to wait and see - but it'll be too late then and some of us will be sorry :) |
| Nigel Atkins |
| It is generally accepted now that modern petrols are more volatile than those used previously, but were there fuel vaporization problems when Spridgets were still being made? Just a thought - why did MG fit air-intake hoses to the later 1500s ? Dave |
| D MATTHEWS |
| I have been trawling the Internet trying to find a petrol in the uk that doesn't contain ethanol. No success as yet and it just gets more depressing reading all the parts of our cars that ethanol likes to destroy. Here was an interesting and credible link http://www.fbhvc.co.uk/legislation-and-fuels/fuel-information/ |
| g Victors |
| I drove to Spain in Jan 1979, and using the local petrol, I often had problems with evaporating petrol at the carbs. As soon as I got caught in city traffic, the engine went wonky, and I often had to pull over to the curb, open the bonnet and let it all cool down a bit. Then I realised it was crap petrol, and after that I always used the likes of BP/Shell or anyone other than the local petrol, which was state run back then. So it's not only a modern problem. |
| Lawrence Slater |
| My fuel overheating problem on my 1500 was fixed by doing the very unfashionable thing of replacing the engine driven fan as well as adding some wing vents. My theory for this was that when stopping in traffic etc the heat from the manifold quickly heated the fuel in the carbs,this leads to the mixture going weak which very rapidly heats the manifold further. The water temperature doesn't react so quickly so the cooling fan does not cut in quickly enough. By this time the car is running very badly with fuel running out from the now boiling float bowls. With the engine driven fan cooler air is constantly flowing through the engine bay and with the wing vents the problem went away. I could easily feel the heat coming out of the vents. Worked for me! Carl  |
| C Bintcliffe |
| Cool vents Carl ! i have side vents, but not even half as big, or as good looking as those. interesting about the engine mounted fan,, sometimes the old low tech solutions turn out to be best.. KISS theory i suppose |
| Andy Phillips (frankenfrog) |
| Carl, Do you have any pictures of your vents from the inside ? i like them and will have a go at copying them (if thats ok with you!) i see from the archive that there was quite a discussion about these in the past... |
| Andy Phillips (frankenfrog) |
| ok, todays installment of fascinating facts and figures.. i wired up a simple circuit that reverses the polarity of the fan and linked it to a microswitch on the throttle linkage. This means that when the throttle is not pressed then the fan will blow air forward through the radiator, but when throttle pressed and the car is moving along it reverts back to its normal 'suck' mode. i let the car warm up until the fan switched on, then had a drive of 20km or so up an A road at about 60mph, then filled with petrol, (whilst leaving the battery connnected so the fan running) then drove home and left it for about 10 minutes, first ticking over, then turned the engine off but left the fan on. Again, colours are: RED line = temp in front of the radiator, so the temp of the air as it comes through the grille before it goes through the radiator . BLUE line = carb temp GREEN line = temp above the battery (highest point and furthes back in engine bay. PURPLE line = air charge temp in mouth of carb. first circled area is stopping for petrol, 2nd is at home with engine ticking over. 3rd is engine switched off. When stopped for petrol the carb and air charge temps are about 48 degs max If you look at the similar situation from my previous drive test, when stopped for petrol thes carb and air charge temps reach 55 degs. OK, an improvement, but much less than i was expecting. The biggest improvement comes when the car is sitting idling for an extended period, with the fan backwards the max temp of carb and aircharge is about 56, but previusly it has gotten to 63 and upto 70 degs... i think the fan reversal is a worthwhile mod, which will definately help the car when stuck in traffic, but i'm not too happy with the throttle microswitch at the moment, it needs to be de-sensitized a bit as you find when creeping along that the fan is constantly changing direction as you change gear and take your foot of the throttle.  |
| Andy Phillips (frankenfrog) |
| Yeah... im STILL waiting for carl to make me a pair of vents...hahaha I difd see.someone posted a link for the big healy fender vents... finally a decent price ..only £155...compared to ONLY $450 state side a few years ago Ive given up trying to make a pair... its way harder then it looks if you dont have the $5000 worth of sheet metal tools Prop |
| Prop and the Blackhole Midget |
| Andy.... Here is a "COOL" modification to cure overheated carbs Eventually I plan to do this...just fir the "COOL FACTOR" of doing this....hahaha Btw andy... how old are you...im 48 http://www.designengineering.com/catalog/cryo2-system-components Prop |
| Prop and the Blackhole Midget |
| Hi Prop, i'm 45... I think the cold air intake will be my next mod but that will be a month away or so as ive got a car show to prepare for and that will involve lots of work to get her presentable. |
| Andy Phillips (frankenfrog) |
This thread was discussed between 09/05/2013 and 15/05/2013
MG Midget and Sprite Technical index
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