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Q: Coolant system temperature oscillates - 2001 Hyundai Santa Fe

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Coolant flush done past weekend due to replacement of coolant temp sensor. Yesterday the upper radiator hose and the connection to the engine with the hose were replaced due to a leaky connection. Those components have been replaced and today I replaced the radiator cap because the original one had very small pieces of rubber missing from the relief. Fan cycles properly Waterpump works because the car wont go beyond 205F No coolant leaks can be seen anywhere on the engine or on the ground Coolant reservoir maintains proper level No sign of white smoke from the tail pipe no matter cold or hot start up When at idle or very low speeds engine temp will rise to about 205F and then oscillate between that and 180F due to electric fan starting and securing. Above 35MPH, the car cooling system will maintain normal operating temperature without the slightest drift(185F). I'm not sure what else to inspect to see what is causing the temperature to oscillate like it is. Radiator was flushed twice.

My car has 279000 miles.
My car has an automatic transmission.

Hi there. With having your radiator flushed twice and having a thermostat replaced, I believe that the problem lies within the water pump. There is a build up in the water pump and is causing the water to fluctuate. Remove the water pump and check it for sludge. If there is sludge, then I suggest replacing the water pump. With the pump off the engine, remove the thermostat and flush out the engine with a water hose on high.

Put the water in the same direction that the water pump creates flow and leave the water hose in for about 5 minutes with the engine off. Put the new water pump on and fill up the system with new coolant with a protection of the highest rating.

If you need further assistance with your vehicle, then seek out a professional mechanic, such as one from YourMechanic, who can come to your location to diagnose exactly what is wrong and replace the water pump if needed.

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