kauai_diver

Target temperature after very hard consistent driving on the track. I couldn't even get close on public roads or I'd be dead or in jail.

1999Porsche911

The DME setpoint for engine temperature is between 90C and 95C. You could'nt maintain a coolant temperature of 175F even on the coldest day of the year driving at highway speeds.

i.e. Your guage is useless.

kauai_diver

That's engine temperature not coolant temperature, can you provide more information than just saying these gauges are "useless"?

1999Porsche911

Hook up your scanner and look at what the temperature is. Engine temperature is the same as coolant temperature.

OCBen

No, engine temperature is not the same as coolant temperature, unless that's a jargon convention used among mechanics, even though it would be technically inaccurate.

An engine has many thermal gradients throughout the engine block. At the cylinder walls, piston caps and heads where the explosions of combustion take place, the temperatures are the hottest - natch. It's the combustion chambers that are the source of heat in an internal combustion engine, otherwise known as a heat engine in engineering parlance. The sole function of the heat management systems in an engine is to get rid of this heat as efficiently as possible.

In a water cooled engine the coolest temperatures are at the coolant inlet where the thermostat is typically located. And if the water temperature sensor is located here - where it typically is - these temperature readings are the coolest temperatures in an engine. From this point on, all temps will be hotter throughout the engine. So we have the hottest engine temperatures at the combustion chambers and the coolest engine temperatures at the coolant inlet.

The oil temperature is generally more indicative of what might be regarded as the 'average' engine temperature, provided no heat exchanger for the oil is being used. And the term 'engine temperature' would more accurately be described by oil temperature. It should be obvious that oil temperature will always be hotter than coolant temperature, since all temperatures beyond the coolant inlet will always be hotter.

1999Porsche911

Engine temperature in a water cooled engine is traditionally coolant temperature. Targeting a specific area of an engine to measure is not engine temperature but temperature of an area in the engine. Since coolant's purpose is to cool the engine, measuring its temperaature is a consistant way to measure the engine's cooling ability. I guess the only way to determine exact engine temperature would be to measure every square inch of the engine and average it out but all those sensors would probably add substantial weight to the car. .

But rather than have a debate about it, the fact is, when Porsche refers to engine temperature in the 997, they are referring to coolant temperature and not oil temperature and their targeted coolant/engine temperature is 90-95C.

yemenmocha

I went up some steep hills at slower speeds due to traffic in very hot weather in the AZ summer and it read over 175 until I reached the top and was able to reach normal speeds again. No hard driving, just less airflow and high temps.

OCBen

Like I said, that may well be the convention. Not really. All you would need is just the two temperatures at the extremes, sum them and divide by 2 to get the true avg engine temp. You already have the coolant temp - all you would need is one additional probe at one of the combustion chambers to get an accurate read of avg engine temp if you wanted to.


But since the coolant temperature does not fluctuate appreciably, because it is after all well regulated, the only measure we have of an engine running hot or of being cold is the oil temperature. The coolant temp will climb quickly to 175 after startup because the thermostat shuts off the cooling system until 175 is reached and then it stays there for the most part the whole time the engine is running, while it takes a good long time before the oil temperature reaches normal operating temp. That's why you and any other sensible driver will wait until oil temp has reached normal operating temperature before placing your engine under heavy loads such as high revving while on the track.

1999Porsche911

Actually, the coolant thermostat is not open until 182F and no 997 can maintain even close to a 175F coolant temperature regardless of climate. Coolant temperature DOES fluctuate appreciably, unless 20% is not appreciable. Because the 997 has a water/oil cooler, your coolant temperature has direct influence on oil temperature based on the efficiency of the cooler. The higher your coolant temperature, the high the oil temperature. Once the ratio is identified, you can determine the oil temperature from the coolant temperature and coolant temperature from oil temperature. (relatively close).

I fail to see the point of your argument. There is no way to get the average temperature and your formula of reading the coolant temp and cylinder temp and dividing by 2 will not produce an average engine temperature but only an average of those 2 locations.

But since this thread is about coolant temperature and Porsche identifies both engine and coolant temperature as the same, my statement remains correct.

OCBen

The point of my argument, which you apparently weren't able to grasp , is that oil temperature is a better measure of an engine being at normal operating temperature, or at cold and still warming up, than the coolant temperature reading.

1999Porsche911

No one here even made any statement as to whether coolant or oil temperature was a better measurement. You original post was "No, engine temperature is not the same as coolant temperature...." I simply corrected you.

OCBen

No, that was not my original post. Allow me to correct you. You omitted the qualification, which stated that engine temperature is not the same as coolant temperature, unless by convention it is regarded as such.

1999Porsche911

And, it is. Case closed.

kauai_diver

Case not closed.

I agree the oil temperature gauge is better indicator of engine temperature, and use that as a basis before going full bore at the track.

What I really want to know about is this so called "useless" coolant gauge.

1999Porsche911

I agree that in your case, since you do not have a properly fuctioning coolant temp gauge that you should use the oil temp as your quide to engine temperature. With a water/oil cooler, you don't need to know your coolant temperature anyway if you have an accurate oil gauge.