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Q: Overheating Under Load

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So my 1995 4runner has been overheating in a strage way. This has happened a few times at a air temp around 70 and again not as bad at 40 degrees outside

This only happens at highway speeds when I step on the gas to go up a hill. I never let the temp gauge go pasf 3/4 gauge but it does climb above half gauge. All other driving including hills at low speeds and freeways that are flat, idling and so on the temp stays at half gauge no matter what.

There is no loss in fluid either coolant or oil. I cant figure this out.

My car has 240000 miles.
My car has an automatic transmission.

A: Hello. To start, you may have a restriction...

Hello. To start, you may have a restriction in the system somewhere. This will come in the form a clog in the radiator, or the water pump going out. Both of these units can be tested individually. The clogs will have to be flushed out, while the water pump will need to be replaced. The clog can be detected with a digital infrared thermometer. The fan clutch may also be going bad. If no extra air is being blown into the engine while its under load, then the engine cooling system becomes overwhelmed. Check this by inspecting the amount of air being sucked by the fan into the radiator. You should be able to feel the amount of air, and it should be a decent amount. Make sure the vehicle is at proper operating temperature when you are testing it. You will have to replace the fan clutch all together if this is the issue. Do some other testing and then decide on the proper action.

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