By July 14, 2008 Read More →

Engine Runs Hot on Steep Hills

Dear Austin,

I have an older Jeep Grand Cherokee. The engine temperature-gauge rises dramatically when climbing long, steep hills. Normal city and highway driving or small hills are never a problem. My local radiator shop quickly diagnosed a ‘plugged rad’ and offered replacement to the tune of $500.

I’m a little skeptical and would like an experienced second opinion: Could it possibly be something else? Faulty thermostat? Fan clutch? Would a cooling system pressure-test help determine the cause?


– Wayne


Howdy Wayne,

I think I would concur with the radiator shop….a plugged up radiator is probably the problem here. The pressure test is the first place to start with overheating problems…you are correct, but I don’t think you have a coolant leak since the overheating only occurs under a heavy load.

These radiators are hard to look inside and inspect, but you can sometimes run your hand along the center part of the radiator when the engine is at normal operating temperature and see if there is a considerable temperature difference between the top and bottom of the radiator. If there is, you have a restriction in the radiator.

I would also check to make sure the radiator is FULL of coolant, since low coolant levels can cause this AND if this model is equipped with a distributor I would make sure the base timing is not set too high. If the ignition timing is “advanced” too much it can cause engine pinging noise/clatter noise like bad gas and cause the engine to over heat under a heavy load.

Advancing the ignition timing is a quick way to add a little more power to the engine…which is normally fine to do unless there is a secondary problem like pinging or overheating.

A restriction in the exhaust system like a clogged up catalytic converter or muffler will not allow the hot exhaust gases to escape…thus over heating the engine. Usually if this is the case, a check engine light is illuminated and engine performance is not what it used to be due to the restriction.

I would not be surprised to see a restricted radiator with a 14 year old vehicle, and it is usually standard practice to replace the thermostat and radiator cap when replacing the radiator.


Austin Davis

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Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

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