Q: Just changed thermostat now my car is running hot worse than before, I think I need to check if the new one is opening up?

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Car was running hot before but not to the point of over heating. Mostly at slower speeds, once on the highway it would level back out to about 180-225. From there I was able to run the A/C, back to 40mph and below had to turn off A/C. I don't know where I went wrong, from my research I assume the new thermostat is stuck closed. If that is the case how would I fix that? I changed the plastic T piece connecting the hoses to the radiator and antifreeze reservoir so there's no more leaks. When priming the car it ran hot and the person helping me wanted me to just let it run even while hot. The car started shaking and said low engine pwr and change oil soon, although it's got a fresh oil change and plenty of oil remain. They said under the hood it hadn't run hot at all, not even bubbling. What else can I try?

My car has 196443 miles.
My car has an automatic transmission.

Overheating can be caused by a number of things such as low coolant levels, a faulty thermostat, 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. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. 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. Lastly, you may have a failing cylinder head gasket allowing coolant to leak from the water passages into the cylinders resulting in the coolant being burnt in the combustion chamber with the fuel. If this is the case, you may also notice a bit of white smoke coming from your exhaust which is a product of the coolant being turned into a steam like vapor. I would suggest having an expert from Your Mechanic come to your home to diagnose your cooling system.

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