Mitsubishi: overheating 97 eagle talon, blown head gasket, pep boys

Question
changed the temp sensor today and it is still overheating to the max. The coolant was dirty and the resevoir had build up in the bottom of it. any suggestions.
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Followup To

Question -
car has only been overheating while ac has been on but the fans are on. we changed the thermometer twice and still does it. we are going to try the temp sensor next but now it is overheating with the ac off it will go all the way to hot and then back down to normal. was just wanting some help with this please.
    thanks, dustin parker
SATURN OF AUGUSTA
PARTS DEPARTMENT
1-706-731-9000
EXT # 284

Answer -
Hi Dustin,

I assume you meant the thermostat was changed? The fact that the gauge moves, although high, that means the thermostat is opening, so it's working. It is quite possible to have a bad sensor sending a high signal at a certain tempeture. I had that with a U-haul truck recently. It ran cool, you could touch the radiator and not get burned but the gauge was pegged hot after driving 5 miles. It was a faulty sensor. Another thing to look at is a blown head gasket, check to see if there is steam or white smoke coming out of the tail pipe. There is also a dye test kit to see if there is exhaust gases in your engine coolent. If you have a check engine light on you should have your car scanned. Pep Boys and Cottman transmission will do this at no cost. If there are any DTC's present then this may help us determine where the problem is. Hope this helps...

Answer
Sorry to be so late with this follow up. If the anti-freeze is dirty it might be clogging up the radiator and other cooling jackets in the engine. You'll likely need to replace your radiator but flushing your cooling system may help. See Pep Boys on this. Before you go running down there though, pull the dipstick for your engine oil. Inspect it for bubbles, brownish color or a white film. If you have any of these in the engine oil you will need to replace the head gasket. If you are mechanically inclined then it shouldn't be to hard. Tidious, but not too big of a deal. Hopefully, the stuff you see in the resevoir is just lack of coolent maintainence and flushing the coolent system will take care of this. Remember to change your anti-freeze at least once a year. Let me know what you found...