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MG MGB Technical - thermostat choices

The reference manuals say that the standard thermostat for the 18G and 18GA motors should be 165F. With summer quickly approaching I'm about to switch out my winter 180 to the cooler one. My question is that a few professional mechanics locally have frowned on my habit. Why? The car definatly runs cooler using my 165 (about 175 degrees on the highway)and when I'm in stop and go in extreme heat (+95F) or climbing long hills, I have a few more minutes of reserve before reaching the 212 mark. What's wrong with running cooler? What is minimum operating temperature?

Thanks,

Paul

Paul Hanley

Paul,
Let me preface by saying I'm not a professional, but I've been around cars a long time. My personal feeling is that when you burn fuel, you release energy that is either used to turn the wheels or is dumped into the enviroment as waste heat. Personally, I'd rather use it to turn the wheels. I think a lot of people overcool their engines. Running warmer improves power and efficiency.

If you look at old cars, they almost universally have low-temperature thermostats. I think this is not because the old engines couldn't take the heat, but rather that the old oils would coke up at fairly low temperatures. As oils got better, thermostat ratings increased.

My personal rule of thumb is that if it's not spewing coolant or running poorly, it's cool enough regardless of what the gauge says. I run a 195 deg thermostat year-round.....

My 2 cents, FWIW....
Rob Edwards

Paul - the minimum operating temperature (in my opinion) would be no less than 165° F. In fact, my MGB doesn't even like to run well at that low of temperature. Keep in mind that the temperature stamped on the thermostat is the minimum temperature that it will allow the engine to run at and has very little to do with how hot the engine ultimately get. Before getting too excited about the car heating up to 212° F, check what the actual temperature of the coolant is with a candy or meat thermometer stuck in the fill neck after the car gets to operating temperature. Your temperature gauge could be reading high. The other thing to consider if you find that the gauge is correct, with a 7 psi cap on the system and a 50% mixture of antifreeze/water as coolant, the boiling point is going to be up around 260° F (Since we are traveling right now, I don't have my chart available to give you an exact boiling point). Even using a 25% antifreeze misture the boiling point is going to be well above 212° F and as Rob pointed out, if the coolant isn't boiling while the car is moving and the engine is not running rough, you are not over heating. Like Rob, I run a 190° thermostat year around and while occasionally seeing the gauge get up to 212° or even as high as 220°, I have never had a problem.

If your temperature continues to climb and doesn't come down when you are moving as a reasonable speed on level ground, then I would be inclined to suggest you look into having the radiator recored with a 4 row L type core from Modine or one of Modine's newer super cores.
Good luck - Dave
David DuBois

Efficiency is higher the hotter it runs.

Since the boiling point of the collant is increased by the pressure cap, the coolant won't boil till it gets up to about 230 degrees F so running a 195 F thermostat is OK and there is no need to panic until the needle gets way into the H region - just don't undo the rad cap!

If you want to buy some more margin then try a higher rated cap - 10 lbs instead of 7. Even replacing an old cap with a new 7 lb cap is worthwhile.
Chris at Octarine Services

Paul when you pull an engine down that has had a low temp thermostat or worse still no thermostat the front cylinder (or cylinders in a v8 )is always a lot more worn than the rear cyls. And I mean two or three times as much wear. This is because of the cold water from the radiator reaching the front cyl first and heating up as it goes back to the rear of the block.You will get a "lot" more miles out of your car at 185-195# than you will at 165#. DENIS
DENIS

This thread was discussed between 20/04/2004 and 21/04/2004

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