Overheating: the real score

Know when your car is about to hit the danger zone
by Ferman Lao | Nov 16, 2009

Hi, Sir Ferman!

Good Day!

I browse various car forums with different schools of thought when it comes to overheating cars so I've just decided to ask the master.

When a car overheats, where should the temperature needle be pointing? Is it right on the red line? Or is a car overheating already when the needle is anywhere above the normal level?

When a car overheats, what are the usual components that need checking? And what are the implications of a minor and a major overheating problem--if they may be categorized as such.

I was really worried because my car reached the ¾ level (not the red line) before I noticed the temperature gauge so I immediately pulled over. I'm not sure if there's any internal damage after my unfortunate plight.

Thanks and more power!

Francis G.

Hi, Francis!

When a car overheats the needle will be pointing to the red zone. The moment the needle goes past the normal midway mark, however, you should be more cautious. Perhaps you can pull over to check if there is anything wrong particularly if the outside ambient temperature isn't hotter/warmer than usual.

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In your case, there is probably not much damage. The ¾ level on most factory gauges is about 105 degrees centigrade. That's over the boiling point of water but still below most coolant/water mixtures boiling point of about 115 degrees to 118 degrees, assuming you are using a 50/50 water and coolant mixture.

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Coolant will increase the boil over point of water but a mixture of more than 50/50 isn't usually recommended anymore.

A higher pressure radiator cap will also aid in slightly increasing the boil over point of your coolant.

As long as the coolant doesn't boil over and is in liquid form it is cooling your engine. But the moment it turns to vapor, its cooling efficiency drops dramatically and this is what you want to avoid.

When this happens and your coolant boils over there will be air pockets in your cooling system, this will aggravate and hasten the overheating of your engine that much faster.

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When your engine overheats the metals expand leading to catastrophic engine failure.

Most automatic fans on late model vehicles turn on at anywhere between 85 to 95 degrees and turn off usually about 10 degrees below the activation point. You can consider this the safe operating temp range of the engine, give or take a few degrees.

Best regards,

Ferman Lao
Technical editor


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