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I have replaced the radiator, water pump, thermostat, 4 fan clutches, hoses, oil looks good, runs at 195 for about 20 mins then slowly rises to 240. If I have the AC on it rises sooner and goes back down once AC is turned off.....what am I missing

Answers from the Automotive Experts

Jessica Howe, Automotive Expert & Coach at


Thank you for writing in. The issue with the cooling system may be a more complex problem that you originally thought. It is typical for the AC to cause the engine to work harder, since it is powered off the drive belt. Running the AC in the summer will always cause an engine to run warmer, particularly in an older vehicle when it is harder to compensate for the extra strain. Worry less about the AC and more about finding the issue with the cooling system. 

Start by checking your coolant. Make sure it is full, new, and the right type of coolant. Secondly, make sure that your radiator cap is properly regulating the pressure within the system. You will then want to double check that your fans are actually turning on, assuming you cannot hear them while driving and know they are working. Lastly, there are a few obscure situations that may be adding to the problem. You may also need to consider the harder to diagnose issus like blocked or clogged cooling passages within the engine, and the even more rare cooling system electrolysis (caused by an electrical current being sent through the cooling system by a shorted or exposed wire). 

Good luck!

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