I am curious as to how useful the engine temperature sensor actually is. It tells you the coolants temperature obviously, but I have read that the engine actually operates hotter than the coolant. For example, oil temperature can vary from 90 degrees Celsius to around 120 depending on engine load.

Hypothetically speaking, if an engine's coolant was replaced with pure or highly concentrated anti-freeze which does not transfer heat as effectively as water, how would this affect the engine's actual temperature?

I would imagine it would increase higher than normal but would the sensor show any indication of this, or would the engine be overheating without the user ever knowing?

Thank you all for your time.

2 Answers 2


Orthodox antifreeze is based on ethelyne Glycol. It does depress the freezing point and raise the boiling point of the cooling system. This is desirable and the suggested concentration is roughly proportional to how cold you think it's going to get. As a coolant, water just can't be beaten so that's why it's still used on the internal combustion engine over 100 years later. In other words, a 100% glycol system would be likely to overheat.

Another issue is the water pump's ability to pump glycol when it's designed to pump water. Even on the Nissan Leaf which is fully electric and as a rule of thumb needs a tenth the cooling of an internal combustion car, there is a mixture of glycol and distilled water. The glycol concentration is higher than 'normal". The design incentive to use pure non conducting glycol for the high voltage power electronics is great but they have added water.


It is common to measure engine temperature at the coolant, however newer systems that are more accurate are taking their place.

While the coolant temperature can vary, the engine is maintained at a constant 93 degrees celsius. This is because, combustion and lubrication is at the most optimum at this point.

The effect on the engine due to the concentrated anti-freeze depends on two things.

  1. Type of anti-freeze. High grade anti-freeze will have a specific heat capacity that is close to that of the coolant itself and therefor will not effect your engine temperature much (Just your wallet).

  2. The cooling mechanism used by the car. If your cooling mechanism is such that it maintains constant cooling rate, then an anti-freeze that is not of sufficient quality will be ineffective in cooling the engine. If however the cooling rate changes with change in engine load then it should still be fine. Cheaper quality anti freeze will make the cooling mechanism to work harder.

  • 3
    Since the engine temperature sensor resides in the coolant, how does it not measure the coolant temperature? Commented Feb 21, 2016 at 11:26
  • 2
    The engine temperature sensor does measure coolant. It is called a coolant temperature sensor. If you run the vehicle with no coolant, the sensor will show the engine as cold while the engine overheats.
    – rpmerf
    Commented Feb 21, 2016 at 18:42
  • That is not the case every time. In systems that switch the cooling on only when the engine goes beyond optimal condition, it will need to know what the engine temperature is and not what the coolant temperature is.
    – krthkskmr
    Commented Feb 22, 2016 at 5:00
  • @krthkskmr Tell us about these special cases where the temperature sensor is not measuring the coolant temperature. Can you be specific about the cars you have seen this on?
    – HandyHowie
    Commented Feb 22, 2016 at 8:24
  • First time I'm hearing this. When the engine "goes beyond optimal condition" the thermostat opens and allows coolant into the radiator. What is "engine temperature" anyways, where exactly on the engine would it be measured? Commented Feb 22, 2016 at 10:49

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