Stupid question about engine cooling...

[Diablos-666]

Sorry guys stupid question alert.

In a water cooled engine how does the water actually cool the engine down when the water temp is at ~90degs itself?

[Megaflow]

Its cooling combustion temperatures of ~700 degrees.

[anonymous-user]

The coolest bit of the engine is warmer than the hottest bit of coolant.

[adyady1066]

Most conventional engines work on a circulatory system. The water is pumped from the rad through the engine, back round to the rad. When the system is hot enough it allows the thermostat to open and feed the matrix. Any excessive flow will be fed back to the expansion tank to allow the system to flow under pressure. If the temp sensor is reading 90 degrees, and the rad is hot, you have hot air inside the cab, it normally means it's working fine. Unless of course you have a VAG type car which you have to check for circulation errors due to a failing/failed pump. Does that answer your question?

[The Black Flash]

And crucially, the system is under pressure so that the water can't boil away.

[adyady1066]

Not exactly. The water system is under pressure which raises the boiling point of the water. If there is a leak in the system, typically from a leaky pump, a seeping pipe or pressure cap in the expansion tank, it will boil away the water leading to suspicions of a failed head gasket through steam as it leaves the system. A good example of this is the rover 'K' series engine. They're known for head gasket failures due to leaking pressure valves in the tank cap. As it can't pressurize it leaks steam at nearing 100 deg where if it was pressured it wouldn't 'boil up' until over 110 deg. It's pure science. Water boils at 100 deg as everyone knows but that changes when it's under pressure in a sealed container. VW Golf mk 3 & 4's used to fail in the same way leaving the system to run dry and thus causing stress at high temperatures to the head gasket/pumps. I've lost count of how many 'k' series engines i've repaired because of this reason. Rover only realised it 3-4 years ago despite making the engine since 1990. What car have you got worries over and what are the symptoms?

[Diablos-666]

Thanks for the responses. I have a better understanding now.

My main query was how water temps of 90 or deg's manages to cool the engine. I didn't realise the engine got as hot as 700degs as the oil temp reads around 95degs.

Where is the water temp gauge usually located, after it's been round the engine but before it goes through the rad (water at it's hottest) to cool down or after the radiator before it enters the engine (water at it's coolest)?

Sorry if these are stupid questions.

[Mr2Mike]

Often in the thermostat housing which is traditionally located at the coolant outlet on the engine i.e. where the hot coolant leaves the engine to go to the radiator.