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Q: Overheating

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My 2005 Buick rendezvous recently started overheating. I have replaced the thermostat and gave it a tune up. The head gasket is fine. It only overheats once in a while. No leaks anywhere.

My car has 140000 miles.
My car has an automatic transmission.

Hi There, This can be caused by a number of things in addition to your thermostat which has been replaced. You may have a clogged radiator or a failing coolant fan switch. As you may know the coolant fan switch helps to maintain the proper coolant temperature by turning on and off at specific temperature thresholds. When this switch is not working properly, this can cause the fans to come on intermittently, all the time or sometimes not at all. When this happens you will notice a temperature spike and drop occasionally as the fan comes on and off. You may also have a water pump that is beginning to fail. Water pumps often times will begin to produce a bit of a whining sound when they are starting to fail. A common problem also associated with this is the water pump may begin to leak around the water pump shaft due to the seal being damaged. In addition to leaking around the pump, you may have a leak elsewhere in the cooling system coming from one of the hoses going to or from the radiator. I would suggest having an expert from Your Mechanic come to your home to diagnose your cooling system.

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