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MG MGB Technical - Overheating

I posted this on the supercharging list, but, in the offchance I get a few other ideas, I'm posting it here.

I'm definitely having problems with overheating. i've got a moss s/c on a 78B with electronic ignition. Timing is set at 10 degrees tdc (being cautious b/c I previously lost the timing and it was way advanced). Mixture is slightly rich, as evidenced by the need to use the choke only for about 30 seconds from complete cold and the #1 plug (#2 and 3 look normal). I live in Texas and summer is here so it is about to get really hot and really humid, so, I'm worried about the temp. I've got a 10" electric fan (installed by po, I'm assuming it is a moss purchase, so probably a hayden unit b/c everything else he did was straight from the catalog) in a puller configuration with(what i'm told is) a 4 core radiator. I have a summer (160 degree fahrenheit) thermostat.

In traffic, in regular temps (85-90 degrees F) the temperature gauge runs up about 3/4 of the way on the gauge. It has also overheated once when the heater valve leaked much of the coolant out. So, I took out the temperature sender and replaced it with a modified unit that has a thermometer in it so that I can tell what the actual temp. of the fluid in the engine block - drill a hole in a sending unit and weld a meat thermometer in place. Here's what I've determined.

In normal driving, normal (85 F) outside temp, mild acceleration (so not really getting into s/c) the engine runs at 200 degrees F. After a short (3-4 mile run) with sharp acceleration, the temperature was at 210 F (with outside temp of 83 F). Today, I started it up and just let it idle. The outside temp was about 78 F. After about 15 minutes of idling, the temp was up to 218 F and climbing. Turning on the heater for 3-4 minutes didn't make a difference. In short, my setup isn't sufficient to cool the engine at idle in normal conditions - normal operating temperature is about 200 F, but the cooling system doesn't drop the temperature at idle and in fact, the temperature continues to go up. Once the temperature hits the mid-90 regularly, i'm not going to be able to drive it during the day. So, I need some ideas on where to go from here.

The setup worked well (even in the summer in stop and go traffic) before the s/c. the radiator was backflushed last year and, I've been told, is in top shape. My first guess is to try a bigger fan - flex-a-lite has a 12 inch fan that has a significantly higher air flow rate (1250 cfm v. 800 cfm) than the current 10 inch hayden that might fit if the lower front brace doesn't get in the way. The other option is an oil coiler, however, without a fan on the cooler, i don't see how that would help cooling at idle.

Any thoughts on where to look/what to do? The timing, while a little retarded, shouldn't be far enough off to make it run hot. the mixture is a little rich, so that shouldn't make it run hot. The cooling system was sufficient pre-s/c to keep it cool and, when the temp was under 80 degrees, run the car at 160 F. It appears that the s/c just creates a lot more heat that the system can't keep up with.
J. Lawrence

I have been using a 165 thermostat and a 50/50 mixture of water (distilled) and antifreeze. I also added a half bottle of Water Wetter (available at most auto stores, Auto Zone, Pep Boys etc.) and the temperature stays at about 165F with no problems. Came home yesterday (300 mile drive) after 1150 miles last week in 90 degree temperatures and the temperature climbed up to just under 190. You might want to give this a try. I have a 1966 B with 96,000 miles on it and an engine that has never been rebuilt.

George Herschell
George R Herschell

The SC will add more heat to your engine. If you don't have the OE fans and using only a 10" Hayden fan, it doesn't move enough air to keep an MGB engine cool at idle and low speeds. The fan will not help at highway speeds. A much better fan is a high output 11" Spal fan. Oil coolers will not make any noticable difference in cooling system temperature. An oil cooler will keep the oil from overheating. You may have to upgrade your radiator to solve the problem. If you plan to use water wetter it works best if less antifreeze is used, use around 20%. I have tried water wetter in a Jensen Interceptor and it helped very little.

Clifton
Clifton Gordon

Good discussion by Les Bengtson attached. Of course with a supercharger you will generate even more heat. Might have to jet-coat your headers and replace your fan?
http://www.custompistols.com/cars/articles/cooling.htm
Robert Dougherty

An alloy head apparently makes a large difference.

I'm running .040 over pistons, flat top, with an alloy 5 port head which has been ported etc.

With a 272 degree cam, stock (original) '67 radiator, late model water pump with the early crank pulley acting as an underdrive, I have no overheating problems. The thermostat is at 195f The fan is the 7 blade plastic fan with the large late model pulley on the fan and the early crank pulley which acts as an underdrive and slows the fan and the water pump. The thermostat is 195f. In a hard grind up a steep grade in third gear at 100 degrees f. the temp will get up to about 210f. I have an overflow bottle and have not had to add fluid in the last 3,000 miles. I'm running 35% antifreeze along with some water wetter product.

I've hooked up the overflow tube to a bottle and have not had to add fluid in a long time, as noted above.

A modified engine being pushed hard with a stock radiator and no oil cooler should produce cooling problems. It appears the problem is the obsolete cast iron head.

Barry
Barry Parkinson

You mention that your timing is set at 10 BTDC, but how much advance does it provide? You could have a total of 40+ degree of advance plus the vacuum advance, depending on the specific distributor.
Jeff Schlemmer

Thanks for the suggestions - I've read every article on Les's (and Bob munchausen's) site numerous times. I think the plan of attack is to make sure I have a 70/30 mix of water/antifreeze and water wetter. I'll upgrade the fan with the biggest one that fits (probably a 12 inch). I'm also thinking of making a fan shroud to see if that helps. Hopefully the bigger fan will make the difference. My biggest concern was that at idle, in moderate temps (75 F), the temperature kept going up, so once the temps stays in 90's all day, there was no way the cooling system was going to keep up. I'll let you know what the bigger fan does. As an extreme measure, I may consider modifying a C rad, however, I would think a current 4 core L type rad should be sufficient.

For what it is worth, if you are looking for a performance mod, I highly recomend the s/c. I live in Houston and have to drive on the freeway frequently where normal speed is 70+. The extra torque at nearly all rpms makes it possible to drive anywhere, anytime, without fear of getting run over. You aren't going to have a car that outruns a mustang, but, you won't be taking your life in your hands merging onto a freeway. Worth every penny spent, and for the type of driving I do, better money spent than "hotrodding" the engine with a fancy cam, oversize pistons, and flowed head. The difference is in the heart of the rpm band where you do most of your driving, 2000 - 4500 rpm.

One last question - flex-a-lite's website states that you shouldn't use an electric fan with a four core radiator. Any idea why? My amatuer speculation is that the four core stifles the movement of air through the core because the cores are too close together and the electric fan can't pull enough air through the rad to provide sufficient cooling. Anyone know?

jeremy

J. Lawrence

My last post was made before reading jeff's question. I have the stock 78 distributor (modified to electronic ignition) so I believe it has the factory curve for that year. At idle (roughly 900 rpm) with no vacuum advance, the timing is about 9 degrees tdc - connecting advance adds about 10 degrees. I don't know the specific total advance under load, but, my mechanic who has 30+ years of experience on MG's thinks the dizzy is fine. The car has 35K miles and the dizzy seems to be in good condition. For what it is worth, advancing the timing 5 degrees to about 14 degrees didn't seem to make a difference. i backed it off out of fear of detonation.
J. Lawrence

Jeremy,

One of the issues at idle when stationary is that the hot air in the engine bay can't escape readily and this hinders the cooling effect.

One "trick" to try if you haven't already is to remove the rubber seal round the rear of the bonnet (hood), this allows hot air to escape while the car is stationary and allows cool air into the bay when in motion as the area in front of the screen is a high pressure area.
Chris at Octarine Services

Chris,

Wouldn't removing that seal allow hot air and (potentially) harmeful fumes from the engine bay into the passenger compartment via the fresh-air intake on the cowl?
Rob Edwards

Jeremy, in my younger "super car" days (OK, I'm telling on myself, but is was in the late '60's), we used to raise the rear of the hood (bonnet) on the hinges (as Chris touched on) to allow hot air to escape. I had a "68 Shelby Mustang with the hood rear raised almost an inch. This made a significant temperature improvement. Rob mentioned harmful fumes entering the cockpit. I never experienced this, but we were not as aware of health issues then. It was common to see cars with and smell "blow-by".
It might be worth the while, to try Chris's suggestion and maybe put a washer or 2 between the hood and hinges. During the "top down" months I think you'll get plenty of fresh air...

Buddy
Buddy Nixon

I have 2 10" fans on my car, these are hanging over both sides by an inch or so. It pushes some major amounts of air (relay to switch, direct power feed off the starter relay.

Also, I don't know where - but an electric water pump at idle??? Just a thought
Frank Baker

Rob,

No - the heater blower fan is so feeble that I doubt any of the hot air from the engine bay would be sucked in while staionary and as soon as you start moving the area becomes higher pressure than the engine bay and the flow of air is into the engine bay.

Most cars I have worked on have grommets missing on the bulkhead that would let more fumes through!
Chris at Octarine Services

I think the heater play is a little different. The heater core does exchange heat and the blower does blow that heat out to your feet (on a 100 + degree day - you need this). One should be able to cool the engine a little better with the heater on. It is a common trick


Another play would be to use an early Mustang radiator (bigger) recored to a modern core (4 row and more effecient) like the V-8 guys routinely do.
Frank Baker

Questions for the experts. Isn't using a 165 degree thermostat the same as not using one at all? Does the 165 degree thermostat ever close? Would the motor be allowed to get up to operating temp (180 degrees or slightly higher)?

J. Lawrence- Have you checked the radiator fins to make sure they are clear of obstructions, bugs, anything that would restrict air flow or insulate the radiator? Have you checked the radiator for internal obstructions that would restrict the flow of coolant? I had an overheating problem that was caused by a clogged radiator. After getting the motor up to operating temp, I felt the radiator for cold spots and found that most of the bottom part of the radiator was cool to the touch whereas the top was hot. How old is your water pump? Old water pumps can have worn vanes and not properly circulate coolant.
Kimberly

J. Lawrence;

I live in SoCal and run a highly modified engine and had engine overheating problems until I made a simple installation that has cured all issues. Here's the secret: Buy the Moss fan shroud for the early engines and install it on your car. It is amazing how much this helps air pull through the radiator, at all speeds. One simple test to perform is to place your hand in front of the radiator and feel how much air is being pulled through the radiator. Without the shroud there is not much pull, with the shroud it is amazing how much more air is being pulled through.

Do this before you spend any other money and see if it cures your problem. You could be saving yourself some significant dollars. If you still have overheating issues, then the next step I would recommend before buying a bigger fan is to remove the thermostat and install the blanking sleeve. You live in Houston and getting up to working temperature is not going to be an issue during the summer months.

Good luck.
Ron Kluwe

Some general thoughts on cooling:

A counter intuitive question: I'm running an "underdrive" on my fan and water pump and am having no cooling problems. -- The early front damper pulley and the late larger diameter pump pulley --. One minor issue is that the alternator won't kick in under 750 rpm. Does that lower pump speed help cooling?

When engine coolant gets hot, a vacuum in the pumping system will locally reduce the water pressure inside the engine and lower the boiling point in that area, causing a steam pocket which does not conduct any meaningful amount of heat. At hi rpms and hi pumping volume, there could be reduced water pressure in the engine and more pressure in the radiator.

I'm also using the late model plastic 7 blade fan with staggered blades. These fans are designed to move air at relatively low rpms. The close blade spacing isn't very effective at high rpms. Does the fan make any difference once you are above 25-30 mph?

In prior posts, I've noticed concern because the engine was running at above 180F. However, with modern hi boiling point coolant and higher pressure caps, the boiling point for coolant is up in the 230F range with only a 7lbs cap.

Water cools in the radiator based on the temp difference between the coolant and the ambient air temperature. The hotter you run the engine, the more the difference between ambient temperature and coolant temperature and the more heat energy that can be dissapated by the radiator. With an engine running at a hi temp you can use a smaller radiator. Modern oils are designed to run in a hi temp engine.

I'm running a 195f thermostat and on a long steep grade on a hot day, with the rpms up and my foot well on the throttle,the temp guage will get up to the 210 level, but there is no problem with losing fluid. ( I do have an overflow bottle and rarely, if ever, have to add coolant) With the alloy head, the heat is conducted away much more rapidily, so there is also no problem with detonation even at those higher temperatures.

In short; is it actual overheating? (boiling and loosing fluid) - or how much is concern because the temp guage is getting too far to the right? Is it something that a higher pressure cap would solve?

Is a water pump designed for a Sherpa truck engine running a low rpms, appropriate for the MGB application?

Barry


Barry Parkinson

"the heater blower fan is so feeble that I doubt any of the hot air from the engine bay would be sucked in while staionary" Can't speak for anyone else but with a heavy cotton cover over my car if I turn on the heater fan it sucks the cover down onto the intake.

Re alternator, they don't kick in until 900-1000 rpm on both my cars, and drop out again at about 600 rpm. If yours starts at 750 then for whatever reason it is better than standard.

Whilst there may be a relative difference in pressure between the pump and the top of the rad and the bottom of the rad and the block, I doubt that the latter is negative with respect to atmosphere, just slightly lower than the former.

If you are talking about the B-series engine in the Sherpa then I'd have thought that as from the factory there wasn't that much difference in rev range in normal use.
Paul Hunt 2

This thread was discussed between 19/06/2006 and 22/06/2006

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