I have a 94 6 cylinder Camry wagon that has just started overheating on the highway and when I get off the hwy until I can find a place to park. The first time it happened I was going about 70 (I’m in California) and noticed that the gauge was at about 5/8. I turned on the heat inside and the temp went back to half but then the heat stopped blowing hot and the temp gauge started going back up. It cooled itself down once again almost to half for a few minutes, then started heating again. This is all in the space of about 5 minutes. By the time I turned the car off, there was a little steam coming from under the hood, but nothing visibly wrong there other than low water reserve.
After about 3 hours I filled up the reserve with coolant and made a 7 minute drive home. After about 5 miles on the highway the temp gauge began to go up again and it seemed like a repeat performance. I parked and looked and the coolant hadn’t moved from the reserve tank. 30 minutes later when I checked, about 1/4 of the reserve tank had been used.
The car has a new radiatior (about 3 years old) and even newer cap, ac functions, and about 3 year old thermostat and hoses. Could it be the water pump? Or something related? Dang.
If it overheats at highway speeds, you either have a 1) clogged radiator, 2) a failed water pump, 3) a stuck thermostat 4) a clogged engine block or 5) the A/C cooler in front of thread is blocked.
The final one is a breached head gasket, which will put combustion gasses into the cooling system and cause over heating.
Since you have a new rad we can eliminate that one. How long ago did you have a cooling system flush? Just changing the rad does nothing for the rest of the cooling system.
You need a good mechanic to check all these things out. My bet is on a leaking head gasket which will need a $900 or so repair.
When the engine is cold, remove the radiator cap.
Start the engine, and while the engine is idling watch the coolant in the radiator.
If bubbles start to appear in the coolant in the radiator, that’s an indication of a breached head gasket.
Tester
You could just have a small coolant leak somewhere. When the engine is cold, look in the radiator not the recovery tank, Make sure the Rad is full. he fact that your heater stopped blowing hot air tells me you are low on coolant.
Filling the reserve tank didn’t really add any coolant to the system. You have to let the car cool off, take of the radiator cap and that’s where you can add coolant. Then you will have air in the system so you will have to run the motor for a few minutes, let it cool again and add more fluid.
You have a leak somewhere in the system. If you can’t find a leak in a hose or clamp then you might have a blown head gasket. You are going to have to monitor your coolant level until you find the problem and get it fixed.
Is the replacement radiator OEM (from the Toyota dealer or equiv.) or aftermarket?
I’ve seen an aftermarket radiator (put on a Honda) crack and leak within 3 years.