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Odd overheating issue

I have a 2001 Kia Rio. Lately, I’ve had odd issues with it trying to overheat. The first time of the day that I drive the car, it is just fine. Doesn’t overheat or have fluctuations in temperature, unless I drive for more than 45 minutes. Then it gets slightly hotter. Every subsequent time after the first I drive it during the day (unless it has been shut off for about eight hours) it gets hotter and hotter. I have not allowed it to reach the red zone, I know better than that. This makes running errands around town a pain. Is this a thermostat issue or something worse?

First of all, check the level of coolant in the radiator. Do this when the engine is cold. The radiator should be FULL and the overflow bottle should have some coolant in it.

Are the cooling fans working? If you let the engine idle after it’s warmed up the cooling fans should cycle on and off to maintain the correct temperature in the radiator. If the gauge starts climbing and the fans don’t come on, that may be the problem.

Thermostats are cheap. I’d install a new one, and a new radiator cap, just to be sure. Whenever there’s a temperature issue the thermostat and radiator cap are the things to replace first.

That type of intermittent overheating is not normally a thermostat issue. It could be a small leak in the head gasket that lets hot gasses into the cooling system after the engine is warmed up. It could also be a faulty cooling fan control that does not turn on fast enough. Since the car is 9 years old, the radiator could be partially plugged as well.

I would take it to a good shop and have it analyzed. If you are lcuky it could be a simple thing like a fan control. The most expensive is a bad head gasket.

The only way I could see it being a T-stat issue is of the T-stat is stuck partially open. Unusual, but not impossible.

Like others have suggested, someone should look at this ASAP. Before the condition manifests itself as a more serious problem like an overheat and a warped head.

Oddly, all of my thermostat failures over the past 15 years have been of the stuck open variety. I haven’t had the THUNK-THUNK reverse peristalsis puking action since the 70’s.

I’d have a hard time figuring this to be a thermostat with the 45 minute onset to first issue. It’s possible, but unlikely. That is, unless there’s some load aspect to it that we’re not aware of.

Have you driven on the highway at all for anything over 20 minutes at sustained speeds? That would assure that both the coolant and oil are fully saturated for temperature and that you’re well into the reserve capacity of the system. You should reach the same temp levels for both over the same 20 minutes in any traffic. It’s just the thermal input:rejection is lower in btu throughput.