By November 7, 2007 1 Comments Read More →

Causes of Engine Over Heating

Hi Austin,

I am now back in Australia, I emailed you back in January and you were very helpful.

I hope its not too much of an inconvenience, but I have a question about another car.

I have owned this MR2 for over year, however it has been laid up off the road for about 9 months, while I was away, I am now back in Australia.

The car was taken off the road because it was overheating dramatically, the radiator was leaking, especially when pressured, when the engine was warmed up.

I have just had the end tanks welded, and seemingly there is no leak there now.

I have just test driven the car and it is still overheating, quickly, much to my disappointment.

I’m not sure where to go from here; I am wondering if there is air in the system; could this cause the overheating issue?

The other thing I did when it was overheating was to turn the heating on full, which took the normal few minutes to come through, however it then abruptly went back to cold, even though I had it turned totally up to hot and the engine was obviously warmed up. Not sure if this is related (I suspect it might be).

I feel terrible about hassling you for advice, however if there is anything I can possibly help you with, I have experience in web development, graphic design and travel, please let me know.

Kind Regards and much appreciation and good will,




Howdy Lucas,


How are you? If you are POSITIVE that there are no coolant leaks and the system is full of coolant, then I would suggest you replace the thermostat first and see what happens. I say that because, with the engine HOT you should have hot air coming from the heater……but you say your heater blows COLD air.


If the air from the heater is cold, then there must not be any HOT coolant circulating around the engine….or at least around the heater core inside the dashboard. So…..I would suspect any of the following:


  1. Not enough coolant in the engine
  2. An air pocket or some kind of restriction in the cooling system not allowing coolant to circulate (feel the radiator hoses and make sure they are both hot)
  3. The water pump is not working, the impeller of the pump has deteriorated or the pump is not turning
  4. There is a restriction in the radiator – the top part of the radiator will be hot, but the bottom of the radiator will be cold
  5. The thermostat is stuck
  6. Electric radiator cooling fan is not working

Keep me posted will ya?



Austin Davis

Reader Update

Austin you are incredible.
I’m not sure exactly how you make your living, but I’m sure you have saved many many people from overpaying less than honest mechanics!
After going through what I had done in my mind, and checking your list, it turned out to be a couple of things; not enough coolant, and air bubbles, but a few of them.

I had ‘burped’ the system, and it appeared full, however I then decided to go and try again, and sure enough, more air. I also found an article through google that revealed there is also a heating system bleed valve, which I was unaware of.

Opened up the valve, and there you go, sure enough more air, and of course then more space for coolant. I’ve now been driving around for a day with no problems, have driven over 100 miles, so it appears fixed!
Thanks so much again for your help, take care and all the best.
Kind Regards,


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About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."
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