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Q: Overheating on 1999 GMC Jimmy

My plastic reservoir is full, when I drive for 10 min I get the eng light on.. Is it the water pump or radiator that needs replacing.. Also I have to put anifreeze in every week
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Get it diagnosed properly for either a stuck thermostat ,bad fan clutch ,blown head gasket.You state that your plastic reservoir is full ,when you drive for ten minutes .Was it empty or low before you start and does it empty out (sucked back in engine/radiator) after it cools?From a cold start (after sitting over night) check the radiator level , make sure the system isn't pressurised , then start it and check the top hose at a safe point.If you can feel bubbling or if the hose is feeling 'tighter' very rapidly (within a minute or two) MY opinion would be a blown head gasket , just get a second opinion before you spend any money (other than coolant for test purposes).Go backwards and re-check the obvious , which we all can often overlook in our initial haste.Good luck.
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