Cool running



Original Poster:

1,762 posts

201 months

Thursday 17th April 2003
quotequote all
I've seen a number of adverts for thermostats that run an engine cooler than the manufacturer's orginal. Why do this?

As far as I recall (from long ago thermodynamics lectures), the higher the engine temperature the more efficient (power and fuel) it will be.

Have I misremembered or is there another benefit in running an engine cool that outweighs this?


133 posts

200 months

Thursday 17th April 2003
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Your are correct in that an engine which runs too cool is not running at it's optimum efficiency.
I have just changed to a stat which opens at a lower temperature than normal to try and avoid the over-heating problems I run into from time to time - normally when stuck in traffic at Le Mans. Basically the cooling system on my car is not quite as efficient as the system the engine was originally designed for (Land Rover Discovery) hence the benefit of the new stat.

david beer

2,873 posts

203 months

Thursday 17th April 2003
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The lower thermostats are a panic attempt to begin the cooling process, in the winter the engine runs cold and in the summer they are virtually open all the time. If go about it the other way,ie cooling fan control you can revert back to standard water stats. My Griff runs the same as my Rangie!


1,520 posts

197 months

Saturday 19th April 2003
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You can buy thermal switches with different temperature ranges to control the fans. A lower fan switch on temperature would be desirable to start dissipating heat earlier before heat soak effects engine bay components whilst stuck in traffic. If you are driving briskly with good airflow through the radiator keeping everything at an ideal operating temperature and then you get stuck in traffic, the sudden lack of airflow and the delay in the fans starting, causes a sudden and tremendous build-up of heat in the engine compartment...

Using a 82/92 degrees thermo fan switch, my Griff fans come on as soon as I slow down. When I put the car away in the garage, I leave the garage door open and raise the car bonnet whilst I wait for the fans to stop running. Once everything is cooled down, normally about an hour later, I close the bonnet and put the dust cover over the car....


26,335 posts

220 months

Saturday 19th April 2003
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Also it works a lot better if you put the otter switch in the bottom hose, rather than the top one. You need a lower temperature otter switch if you do this (since the bottom hose runs cooler) but it turns the fans on and off much more promptly to maintain air flow through the rad as you speed up / slow down.

>> Edited by GreenV8S on Saturday 19th April 16:44