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MG MGB Technical - Overheating, What Next.

65-B Overheaing at idle only. Here is what I have done. Hot water tested three guages and used the most accurate. Within 5-deg. Removed thermostat & put it back. Flow tested Rad by pouring gal of water thru-come out bottom as fast as I poured it in. Push fan installed but does not help. Not adding water and no water in oil. Runs great, What Next??? Running temp 185-195. Idle 195-215.
STEVEN CROWDER

Steven. The next step is to look at what thermostat you have in the car. The thermostat begins to open at the rating on it and is fully open 20 deg F higher, giving full flow at that point. Thus, it mainly affects how hot the car's minimum operating temperature is and has a secondary effect on how hot the engine runs. In your case, a 160 deg thermostat would be fully open at 180 deg F and would allow full coolant flow at that temperature.

Secondly, the ability of the coolant to absorb and transfer heat is controlled by the mixture of water and antifreeze with water having a designation of 1.0 and antifreeze a designation of 0.6. Thus, a 50%-50% mixture is only 80% as efficient at conducting heat away from the engine as 100% water would be. Here in Arizona, I run about 75% water to 25% antifreeze--seldom gets below freezing in my area.

Flushing the cooling system might help--or it might not. Often, there is build up near the rear of the block which has to be physically removed through the opening for the rear core plugs (furthest one back on the right hand side and the rear one).

All that being said, your car is not running all that hot. The antifreeze raises the boiling point of the solution and the pressure cap does also. Hence, your boiling point will be significantly higher than your operating temperature.

Greatly expanded information on the MG section of my website, www.custompistols.com/ under the tech articles section.

Les
Les Bengtson

seeing how fast water pours out of an open rad isn't a good enough test, you need to scan the surface with an infra-red thermometer looking for cool spots.

But running cooler than it idles? Whilst the rad is force cooled when you are running the engine is also developing a lot more heat, and any running temp difference would normally be the other way.

I think you need to be looking at the engine producing more heat than it should at idle, i.e. timing, mixture etc.

And BTW, it's only overheating if it is losing coolant or steaming. In any given ambient temperature as the coolant temperature goes up the efficiency of the rad improves, which tends to stabilise the temperature.
Paul Hunt 2010

My newly built car was running hot but it got better when I put the thermostat in the right way up! It still does get hot. Usually running around 100C but it seems to be getting better all the time as the engine is run in. It has less that 1000km on it still.

I was also considering changing my coolant mixture from 50/50 to something lower. Freezing isn't a huge problem where I live either.

As Paul says check the timing and mixture and so on. What speed does it idle at?

Simon
Simon Jansen

Yous should try running a mixture of 33 1/3% antifreeze and 66 2/3% distilled water, Also, do you know the age of your water pump? The impeller may have corroded to the point where it flows enough water at high speed but very little at idle. RAY
rjm RAY

Might be worth checking the impella is still attached to the spindle on the water pump.Has happend to me before on an old Morris Marina.
a goldup

Steven-
It is possible, although unusual, for a head gasket to develop a small leak into one of the cooling passages. In such as case, no oil would be seen in the coolant. This condition can easily lead to overheating. The simplest way to check for this is to run the engine with the radiator cap removed from the radiator, and look for bubbles in the coolant.
Stephen Strange

I don't think that the cyl head gasket is leaking here. If it was Steven would have noticed the coolong system pressurising and blowing water out of the overflow. To some extent I have the same problem on my roadster. When the engine is idling the temp gauge gradually rises and then comes back down again when you move off. I put this down to poor quality of the modern radiator with the slow fan drawing little air through it coupled with slow circulation of the pump at idle speed. It's been like that for years and never caused any real concern.
Iain MacKintosh

"the coolong system pressurising and blowing water out of the overflow."

Not on a 65, or anything with the header tank on top of the radiator and the filler cap and overflow above that. Any pressurisation will blow *air* out of the overflow, not coolant, unless it is gross pressurisation which would be obvious. My roadster has been doing that for 20 years with no other ill-effects. However with the later remote expansion tanks cooling system is much more likely to blow coolant from the radiator into the remote expansion tank, and from there out of the overflow. BT, DT with the V8. This empties the engine and radiator, *not* the expansion tank, which make the practice of putting a coolant level warning system in that tank instead of in the radiator or block pretty pointless.

To see bubbles you would have to fill the radiator up to the bottom of the filler neck otherwise the bubble will be more likely to surface and burst near the top hose. Quite Easily Done, although easier to put the bottom of the overflow tube in some water and watch that. No air should come out at all, warming-up or running, as the pressure inside the cooling system should always be below that of the cap, except possibly under extreme conditions.
Paul Hunt 2010

UPDATE-After new WP/T-Stat/and all of the other things above, I checked the timing and it appeared to be between 10/12 deg BTDC (Third tab past TDC on my car). I retimed to 15 BTDC and I have seen a 75/90% improvement. Is this possible to have made this much difference? Thanks to all for your help, this site is just the best, been saving my butt for 15+ yrs. NOW, see my next thred for Relays For Dummies.
STEVEN CROWDER

Sorry to disagree with you Paul but if the gasket is gone the pressurisation will lift the level of the water in the rad and blow it out of the overflow. It would only be air if the air managed to rise to the surface first and in my experience this seldom happens. Yes by all means fill the rad to the top and observe if bubbles emit but take care as the water level could suddenly rise and overflow scalding you.
Iain MacKintosh

I did say if it were gross pressurisation it would be obvious, I was responding to bubbles which is to a different scale.

And retarded ignition *will* make a big difference to how much heat an engine generates, as more energy is lost from the burning of the fuel *as* waste heat instead of forward motion. In this case it was idling, but I'm pretty sure you will have had to unscrew the idle screws somewhat as advancing the timing, and the engine making much more efficient use of the fuel, will have increased it.
Paul Hunt 2010

At no surprise, your right Sir Paul. Have not yet set the idle back, but will today. Again, thanks.
Steve C.
STEVEN CROWDER

This thread was discussed between 06/07/2010 and 13/07/2010

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