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MG MGB Technical - Engine runs close to the hot mark

Has anyone else had a problem with their MGB running hot? The engine runs good and has plenty of power, the timing is correct, the thermostat is new, the water pump is new. I replaced the radiator. I have 2 fans in front of the radiator.The only time it uses oil is when driving in the mountains.
Robert sewill

Robert - Have you stuck a thermometer into the radiator to see how hot the coolant really is? you could have a temperature sending unit that is bad, a gauge that is reading high, or even a voltage stabilizer that is not doing its job (what about your fuel gauge - does it also read high?). Next question, what temperature is the thermostat that you have in the system? A 195°F will result in the temperature gauge to read about half way between N and H, but it is a perfectly good level to be at (I run a 195°F thermostat in our MGB all the time). Keep in mind, a car is not overheating unless it is boiling (emitting steam) while the car is in motion. Cheers - Dave
David DuBois

Hello Robert-For $29 at Harbor Freight you can own an infrared thermometer that can read your warmup temps, tell you what temp the thermostat opens, and when aimed at the sensor, tell you what temp it should be reading and how "hot" the block really is. Darn cheap insurance me thinks. Cheers, Vem
vem myers

Robert, I'll second Dave. You said, "The engine runs good and has plenty of power, the timing is correct, the thermostat is new, the water pump is new."

No worries! :-)

I'll also second his vote on the 195ºF thermostat. That's what I run as well. It was 104ºF here in NC yesterday, and the temp gauge in the B read from half-way between N and H and all the way up to H on the drive home -- but the car never overheated and ran just fine.

You might consider fitting a 16psi radiator cap if you haven't already done so. Every 1psi gives you an additional 3ºF overheat protection. With a 16psi cap and a 50/50 mix of water/antifreeze, you won't overheat until well above 250ºF!
Rob Edwards

Robert-
What ratio of coolant-to-water are you using? The "thicker" the ratio, the lesser the efficiency in terms of heat removal, both inside of the block and the radiator. As a coolant medium, water has an assigned cooling value of 1.0, while unadulterated antifreeze has a cooling value of .6. Thus, antifreeze is only 60% as efficient at heat transference as water is. A mixture of antifreeze and water is thus not as efficient at heat transference as pure water is. The formula for determining Coolant Efficiency is [(Percentage of Water X 1.0) + (Percentage of Antifreeze X .6)] = Coolant Efficiency. I prefer a mixture of 75% water and 25% antifreeze that results in 90% Coolant Efficiency. [(75% x 1.0 = 75%) + (25% x 0.6= 15%)] = 90% Coolant Efficiency. That is a 12.5% improvement over the most common 50% / 50% mixture which would be only 80% as efficient. This would have a somewhat similar effect as adding yet another row to a four-row radiator matrix.
Stephen Strange

Stephen -- I don't have a bottle handy to consult at the moment. What would by the boiling temp of a 75/25% mix at atmospheric pressure?

Cheers!
Rob
Rob Edwards

Rob-
25% ethylene glycol + 75% distilled water will boil at 218 degrees fahrenheit. 75% ethylene glycol + 25% distilled water will boil at 252 degrees fahrenheit.
Stephen Strange

So 218ºF + (3ºF/1 psi * 16 psi) = 266ºF before it overheats. That's not too bad....
Rob Edwards

Rob-
If you filled the cooling system with the common 50/50 premixed stuff, you should be able to easily switch to a 25/75 mix. Store the 50/50 stuff for winter use, and then be sure to use distilled water when you make your own mixture. Also, be sure to flush and descale the system in order to remove the 22+ years accumulation of muck, rust, and mineral deposits that act as insulators that retard heat from being dispelled by the coolant system. If the heat is trapped in the metal of the engine, your water temperature gauge will not tell you. It measures only the heat in the coolant. The trapped heat has to be removed by the lubricating oil, which will shorten its useful life. You will be surprised at how much cooler the engine will run in the summer and how much warmer the heater will be in the winter.
Stephen Strange

Hi Stephen,
Was that addressed to me or Robert Sewill? I like running my engine as hot as practicable. I've had no issues with 50/50.
Rob Edwards

This thread was discussed between 29/06/2012 and 02/07/2012

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