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Engine gets a little warm at idle and no heat till I rev it up

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Fahrenheit

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On my 03 GT with 100k on it. Like the topic says, heater blows cold and engine gets a little warm but if I rev it the temp drops and heat comes back. I'm thinking its the water pump, what you guys think? Anyone got a write up handy on how to replace it?
 


Personally, it sounds like a clogged heater core/cooling system to me. Think about the flow. At idle the pump is turning slower, so flow is lower through the core, even more so if it is clogged or partially clogged. Then when you rev it the flow rate increases and pushes more through the core, thus increasing the heat you feel inside. The temp dropping on the gauge is normal to me. Increased RPM's=flow=more cooling=gauge drops.

That's just me thinking outloud. Never had a pump fail to push coolant, usually they just wear out the bearing or leak externally.

Then only other thing that comes to mind is air in the cooling system. You don't have a leak anywhere do you? Disturbed the cooling system lately? My 00 GT used to do this and flushing then bleeding the system fixed it. I have great heat even at idle and the temp stays where it should.
 
If it doesn't get warm probably a thermostat, probably a good time for a flush when u change it.

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Thanks guys, over the summer I was flushing the coolant system with water to get dex sludge out of the system. Maybe I got an air pocket in the system. Ill try bleeding it tomorrow. Just seems strange that I had good heat last week but now I only get it above 3k.
 


Before you bleed it, with the car cold pop the cap and make sure it's full on coolant, and check the resevoir as well. If both are full, then bleed away. If not then top them off.

If low you could have an external leak somewhere, or the LIM gaskets are leaking internally if they have never been changed.
 
LIM never been changed, was planning to do it this summer. Oil looks good at the moment. Did have to add coolant but I normally do a week after I flush out the coolant. Ive been flushing clean water to get the dex sludge out. Last week it got anti freeze for the first time.
 
i have a 2007 Grand Prix with the exact same problem. it has 70k miles on it and still has engine and transmition warranty from the dealership that i bought it from not even a month ago. if i floor it then it will cook me, but at idle or just driving like a normal person i get little to no heat. its warm but not warm enough to heat the car up.
 


Seems like it was an pocket. Got under the hood today (so cold out!). The rad cap was ice cold even after driving home from work (about 50 min drive). Though that was odd, reservoir was filled as well. Top rad hose was also hot. So what I did was toke a large towel and placed it over the red cap and removed it. The engine was still hot at this time. When the seal gave way I got about 2-3 secs of air hiss before hot coolant came out. Cranked it back down and on the drive to work tonight the heat worked fine and the temp didn't go or down with RPMs. Problem solved!


Disclaimer! Never remove rad cap while engine is hot it will burn you up!


Also when I went to close the hood the latch was forzen, guess thats what 11 degrees does to it lol. Got that fixed with a little WD40
 
Yea, removing the cap with the engine off and hot is a good way to evacuate the contents of the cooling system rather quickly, lol.. been there done that. Makes a mess of everything and coats the belt and pulleys in coolant too. Good that you have heat again. You may want to try this again once the motor is cold (like let it sit overnight) and then top it off if need be.
 
Your heater core is clogged. Pull off the hoses blow some compressed air through it and watch the sludge come out

Sent using my Galaxy SIII on Tapatalk 2
 


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