I bought a used 1995 Lumina a few weeks ago with 80k miles on it and yesterday it began overheating. I changed the thermostat, water pump and flushed the cooling system so it's not plugged and there are no leaks. The fan kicks on as it should and the head gasket checks out. The oil is fine along with the coolant level. The engine runs fairly smooth with no pinging or knocking but it keeps overheating anybody have any suggestions we desperately need to get this vehicle running and don't have alot of cash to do so.

 

if you changed the thermostat make sure it is in the right way.

how do you know outside of the dash gauge it is over heating?

if the pump is good and all the fluid is full and the radiator is clear, then it`s the thermostat.
is it a manual thermostst? (opens with heat and not a sensor)
i would take the thermostat out and run it and see if it still over heats.

even new(remanufactured) water pumps can be bad right out of the box. along with new thermostats.

it also could be a bad sending unit for the temp gauge giving a false reading.
that`s why i asked why you thought it was over heating. if you have a heat sensor gun shine it around and see what it reads.

 

You left out the radiator. And even if you can make hose water easily pass through the radiator, does not necessarily mean the radiator is clear, good enough. I know. I have been there done that. A new radiator fixed fixed me up.

A tip off is with cap removed if when the water starts to circulate, if the bulk of the coolant tries bubbling right out at the now open top of the radiator where cap screws on.

Another tipoff is if the car runs hotter going down the highway and cooler around town. Any engine runs hotter on the highway, requiring more cooling, due to the car fighting wind resistant, causing you to have to step on the gas pedal more to make bigger explosions per stroke, and other factors, like tires heating up more and getting softer and who knows what else. If you take it out for a spin on the highway and you see the temp getting higher and higher, so you quickly return to town and find after driving slow in town, that the temp starts coming down toward normal - suspect the radiator partially plugged.

And if the radiator is slightly plugged, it cannot keep up with that effect, as the radiator was designed from the factory to handle the cooling needs with the radiator passages fully open - not partially clogged.

 

Check to ensure the thermostat is the right way - good point.
Put the front of the vehicle on ramps or jacks. Take off rad cap with engine cold/ start engine / get flash light.
Look into the rad with light, do you see coolant? Can you see it flowing?? If not....
-rad is plugged
-heater core is blocked
-bad water pump.
If there is flow, you need to bleed the air out the system since the coolant change. Let it run and watch the flow. you can also put your hand on the rad hoses to feel flow.
Ensure coolant level is correct in rad and expansion tank.
Use a 50/50 mix of coolant and dis-stilled water / bottled water.
Is the rad scaled up inside?

 

How do you know the head gaskets are fine ???? Are you adding any coolant?? Pull the sparkplugs & if any of them are really clean & white you're into a gasket.. (head or intake). Do you have a bra on it or other aftermarket acessories that could restrict or direct airflow from the rad area?? Are there a lot of bug & stuff in the external fins of the rad??? Lots of stuff,,but hopefually nothing serious... Roger