Question about 1999 GMC Jimmy

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Heater goes from hot to cold

1999 gmc jimmy vehicle not overheating but after temp gets up to norm heater will occasionally blow cool. Should this vehicle have dex-cool antifreeze? Currently it has regular (green) antifreeze could this cause my problem?

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  • krazy_tat2 Jan 23, 2009

    I have the same problem in a 97 Jimmy. Put a new thermostat in and still blows cold. Should I get rid of the dex-cool? Maybe a vacuum line? It does it on the highway or sitting in the drive for 30 min.

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I WAS TOLD IN THE PAST TO GET RID OF THE ORANGE ANTIFREEZE AND PUT IN THE GREEN IN ALL MY VEHICLES CREATES MORE PROBLEMS THE IT CURES THIS IS BY A SHOP I TRUST.I HAVE A 95/98 AND 99 BLAZERS.I HAD PROBLEM WITH VERY LITTLE HEAT AFTER CHANGING THERMOSTAT. HAD TO GET AIR OUT OF LINES BUY RUNNING IT FROM COLD START WITH RADIATOR CAP OFF UNTIL THERMOSTAT OPENED AND LEFT IT RUNNING UNTIL I SAW NO AIR BUBBLES COMING OUT OF RADIATOR SEEMED TO CURE PROBLEM

Posted on Dec 20, 2008

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If you pay close attention when it starts to blow cool, you might realize you are probably accelerating, going up incline or something that causes you to push pedal down a little more, indicating a vacuum leak somewhere in the system, or a faulty check valve in a vacuum line that feeds the heater controls. It will probably switch back to warmer when you let off the gas & coast for a while. Is that the case?

Posted on Dec 13, 2008

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