Why does my car keep overheating?

Did you check the thermostat. That is at the end of the upper radiator hose and engine block. If that is stuck close it will make you car over heat.

OK.......let's get down to brass taxes.

most GM cooling fans kick in 212-226 deg. F roughly.

Start the engine (with plenty of coolant in it) and put your hand on the upper radiator hose. It should wait awhile until it suddenly gets way too hot to hold. The thermostat has opened at this time. If the system start boiling and regurgitation and overheating before then........replace the thermostat and keep reading.

The "sniff test" checks for CO2 gas buildup in the cooling system in the event of a blown head gasket. If gas is building up (depending on severity) the hoses should harden up quickly during warm-up. If this is true, there will always be air pockets in the cooling system until the cylinder head gasket problem is dealt with.

the fan should come on about 180, if not the electric controlled switch could be bad, there is a sensor that detects the temp and turns on the fans, this is probably not working thats why it will run hot, other that a cracked head or a clogged cooling system that besides the water pump will be the most likely problem, if you live in the south where the ambient temp is high i would add another fan too, it would have to be installed on the inside of the radiator because with the 2 fans on the front of the radiator there is not room for a third, , those 3.8 l engines do not do well with alot of excess heat

like others said check the thermostat and the radiator. But you may want to lookin to when the car is supposed to kick in and on what premesis you are saying the car runs hot. The temp gauges on the GM's tend to be poor indicators of what the real temp is. Find out what the stock temp is for the fans to kick in, make sure its right. If not check the Temp senders and the relay for the fan. If avail use a temp scan tool to check the temp on the radiator. This will help you make sure that the temp on the radiator is consitent and that there are no cooling problems in the radiator itself. Also you may want to check the condition of the radiator cap, if it too is failing to open or stay shut at the correct psi/temp you can be heating up too easily from not being a fully closed loop system. You may also want to follow up with whoever it was that installed your heater core and let them know you are suffering these problems since you have had the part installed and you can't even use it. They may have screwed something up too. It's a lot to digest, but its all a trouble shooting process, good luck. oh, hows your air filter? my GF's car was runnin hot cause it was a high fuel low air situation in the combustion chamber caused by something that was stuck to her airfilter, oh and her GM's fans are set to kick in at 212 deg and turn off at 206 (but they all very, look up yours), hope this helps.

With the age of the car, the water pump could be bad, look to see where the coolant is coming from. Is it a hose, water pump, or the radiator. There is also a heater bypass hose on the waster pump, I think. The first thing would be to change the thermostat with a new one. It's not hard to do and that may solve your problem. Do find the coolant leak and get it fixed. It could be something simple or something like a head gasket or intake manifold gasket. Besides you never know when you'll need to be somewhere and won't have the time to put more fluid in and you could overheat the engine.

That particular engine is prone to blowing head gaskets when it has been run hot. Since you say it is skipping now, this may well be the case. The thermostat probably should be changed also. Have your mechanic do a sniffer test before he tunes it up.

The heater core has nothing to do with the cooling system, except the fact that they both use the same coolant. When you changed your heater core, did you bleed the system? If you did, I would suspect the thermostat. Thermostats are cheap and easy to replace. If this doesn't solve the problem, I would check the engine coolant temperature sensor.

Good Luck!

Make sure the water is circulating if not may need a water pump and or thermostat change both if still gets hot hope this helps

Get the pressure of the cooling system checked to ensure proper circulation of coolant. Check thermostat and cap.

Check the thermostat