No previous overheating problems[hr]I have run my car with AC on in parking lots many times before with NO problems. Then, I let the car run for a brief period in the parking lot at a fast food place with the AC on. It started overheating. When I got going faster on the freeway, the temp. gauge suddenly dropped from hot to normal temp., then gradually heated up too much again, then suddenly dropped again. Then it got hot again and stayed, so I pulled off the freeway and let it cool off. After cool, I refilled the fluidsthey had boiled out of the overflowI had to replace about a gallon and a half of fluid. Can anyone tell me: What would cause the car to suddenly overheat. The fluids were at normal levels before this happened. Would this be a thermostat issue? Could the thermostat be sticking? If so, where is the thermostat? On the top hose or on the bottom hose by the water pump? Or is this a fan issue? What is the best way to check the fan?

 

Its easy to find out if its the fan pop the hood turn your car and ac on and watch and see if the fans stay on. I think another problem could be is that the hose leading from the coolant is a bit clogged. That happened in my dads 4runner. I was driving it and it over heated out of no were. I then took it home and checked the car. It was very low in coolant and I filed it up but the car over heated again. So I took the hose off and that's when I noticed the clog. I took it and soaked it in hot water and then used a pressurized hose and it cleanned it very nicely. I let it dry and put it back on and the car never over heated again

 

check the type of coolant u used b/c this happened to mine and someone put the green **** in mine and il ltell u i ended up needing to get the engine reconditioned for 2 grand so if u had dex-cool (red coolant) in it which is what is supposed to be in it then u put the green in there it will cause clumping and that would obviously clog the entire cooling system which wouldnt be good

 

If the temp is going up and down on the hwy check the T-stat. Follow the lower radiator hose to the engine block to find the housing.

Could be a hose but, as is when the system is drained of coolant to access the T-stat look inside the radiator hoses.

The autozone website should have info on changing the T-stat.