Please Help

In my car the temperature gage will go up to the high point not the red and will come back down once it comes back down the heater starts working. I had the thermostat changed in July. Do you have any ideas?

While it could simply be a matter of a low coolant level, give us specifics about the vehicle, please. Year, make, model, etc.

The coolant level was fine. It is a 2000 ford explorer 4.0

There still could be a bubble of air in the cooling system. Are you checking the level in the radiator itself or just the overflow tank?

If the coolant is completely full, change the thermostat and radiator cap.

When the engine is cool, take the radiator cap off and make sure the radiator is full of coolant. The overflow bottle should be about 1/2 - 3/4 full. The radiator may not have been completely filled when the thermostat was changed; or, the cooling system has a leak. Either way, fill the radiator with anti-freeze coolant. After a few days, check the (cool) radiator level, again. If it’s down, there is a leak, and you’d need a mechanic to fix it.

I,ve had this problem crop up from time to time. The fix I use, from an old mechanic’s trick, is to drill a small hole, like 1/8" or smaller in the flat part of the thermostat. This provides a bleed hole for trapped air to escape. The small hole will also prevent too much coolant flow to by-pass the closed thermostat. It works, and I use it every time.

I helped a friend with that same problem years ago. He replaced a thermostst and had the same problem. After a few hours I took the thermostat out and discovered the new one in backwards. Not good for car.

You still need to take it to a mechanic for pressure testing and other troubleshooting. The engine cooling fan may not be coming on, the coolant flow through the radiator may be inadequate, and other things. Have you tried flushing the cooling system and putting new coolant in? Internal leakage, especially, needs to be repaired, soonest, before serious damage is done to the engine. The cost of a mechanic’s services is less than the cost of an engine. Choice.

This is a classic symptom of either low coolant or a head gasket failure. Could be a bubble in the system though as others have said. A pressure test is in order as well as checking for gas bubbles in the radiator. IMHO anyway.