Our 'new' ('07) Cobalt has a digital temp readout. Temperature varies substantially, depending on driving conditions - I've seen it as high as 210(F) on city streets, on a not-very-warm day. Our old Cavalier, and every other car I've owned, just went to 195(F) and stayed there.

My initial thought was that the fan wasn't coming on. But, googling, I get the idea that the fan doesn't even start until 223F.

Which is my question: just to be sure we're not frying the engine ... is that really true? And, not that I can do anything about it, but are they sure it's a good idea?

3 Answers 3


I'm guessing you've got a 13 psi radiator / cooling system cap. The 13 PSI number is pretty standard for GM cars. At that pressure, water doesn't boil (from liquid to vapor) until 245 deg F or so. What you are seeing is totally normal. The manufacturer uses those pressures to improve radiator vehicle cooling performance.

If while driving on a hot day the gauge never gets above 212 Deg F, that would be a big problem (indicating the radiator cap wasn't controlling pressure correctly.)

I would guess the range of your temp would be between 195 F and 235 deg F or so during normal operations.

And one suggestion... for a good investment in your vehicle, consider a Chilton / Haynes $30 paper repair manual. This stuff will be explained in there, and help you maintain your car as well.

  • Why spend $30 on an antiquated "book" when he has us?
    – JPhi1618
    Apr 13, 2016 at 14:02

The thermostat opens at 180 degrees F, this sets the lower limit. The fans come on in low speed mode at 223 degrees F. The fans come on in high speed mode at 230 degrees F. So temperature can and will vary between these values. In cool weather when driving at higher speeds the temperature should be in the lower end of the range. On hot days with the A/C on at idle it might move toward the upper, high speed fan, range. If it consistently runs in the upper end of the range testing may be needed. If it drops below 180 replace the thermostat and retest.

In recent designs there has been a move toward higher maximum temperatures.


It all depends on what temperature the thermostat is designed to regulate the coolant at, which usually depends on what pressure the cooling system is designed to operate at.

Water boils at 212 deg F at atmospheric pressure but will boil at higher temperatures under pressure. This is why it can make sense for the fan to turn on at 223 deg F; the coolant would still be liquid at that temperature.

  • It's the science again. Apr 13, 2016 at 5:49

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