Heating SUV

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prairiehotrodder
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Heating SUV

Post by prairiehotrodder »

I could use some suggestions for fixing my Buick Rendezvous. I'm about pulling my hair out with this piece of junk. Its an 03 with the 3.4 L V6. The heat comes and goes. I replaced the thermostat, that didn't help. I did the head gaskets and rebuilt the heads. Checked the water pump it looks fine.
If you start it cold and let it sit and run it will get really hot (motor temp) but not blow heat out the vents. When i drive it the temp stays fairly normal and only blows heat when its revved up a bit or working harder. I flushed the heater core and it seems fine. Coolant flows through it easily when i flushed it but not when its running. The heater core is a nightmare to change on this thing. I'll change it if i have to but i can't see why it wants to overheat at idle but goes down the highway just fine.
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Re: Heating SUV

Post by ProPower engines »

Sound like you have the dreaded air lock in the system.
Most new vehicles require the heater system to be thoroughly bled while the engine is running.
It is a PITA but we used to have special clamps and related hose connectors for alot of the modern cars and trucks and SUV's.
The systems at times have a high point bleed plug of some sort or you must run the engine and remove the hose/hoses as needed to get coolant flowing.

The heater core can be flushed in reverse by flowing water from a hose then adding NO more then 3-5 psi of shop air in short blasts to shock loose any build up within the core.

The option is about 10 hrs of R+R time on the heater core if the air shocks don't work [-o< [-o<
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Re: Heating SUV

Post by S10LS2 »

^^^ "The heater core can be flushed in reverse by flowing water from a hose then adding NO more then 3-5 psi of shop air in short blasts to shock loose any build up within the core"...
This is your fix. Do exactly this. I have done it on half a dozen Gm trucks 1999-2008 ish. When the owner complained of very little heat and everything else checked out ok. Reverse is the key, along with the air. Worked everytime.
Last edited by S10LS2 on Sat Feb 23, 2019 7:08 pm, edited 1 time in total.
Roundybout
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Re: Heating SUV

Post by Roundybout »

Does that have rear heat by chance? I had a Buick Terraza that had similar symptoms and it was due to the rear heater core plugged. Looked like a lot of rubber particles in it.
S10LS2
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Re: Heating SUV

Post by S10LS2 »

Would not be surprised if the radiator is partly clogged as well.
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Re: Heating SUV

Post by BOOT »

Could be the door that switches from cold to hot air or outside vent. I'm no interior expert but my 09 Silverado the hot/cold dial sticks on cold after using AC all summer and you have to play with it a lot to get it to go over to hot then leave it alone for the rest of winter.

edit: Well I assume that door thingy from all the cars I've stripped down for weight reduction LOL
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Re: Heating SUV

Post by rfoll »

If the engine ran DEXCOOL it could have caused a problem. When the orange coolant comes into contact with air, it forms a muddy solid that is very abrasive and will clog the radiator and heater. I remember reading somewhere that some of the GM engines require flow through the heater core to circulate as intended.
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prairiehotrodder
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Re: Heating SUV

Post by prairiehotrodder »

The heater hoses are a real brute to get at. There is one hose that has a loop in it and goes up real high. I sliced the hose and a big whoosh of air came out. I then put some elbows into it and ran the hoses to a flush tee out in the open. I topped up the coolant and the temp gage now quit being so erratic. The temp and the thermostat acts as it should. It now blows a little heat but not that great. At least its driveable. This has been the coldest winter in over 100 years here. Thanks for your suggestions. I may still check the blend door as mentioned.
I'd like to find some thin ice to get rid of this thing but there isn't any !
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Re: Heating SUV

Post by makin chips »

Had this issue with a 3.1L Buick. It ended up needing a new thermostat again because the first replacement stuck open, also. It's been a couple of years but that's what I remember. It had more heat than before I replaced it initially so I figured it would be OK. It wasn't. As long as the car idled, it would blow warm air but as soon as you started driving, it blew "cold" air.

I'm guessing tstat is stuck or sticking open or the heater core is clogged enough to not work like it should. Had that happen in a GM recently, also.
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Re: Heating SUV

Post by Schurkey »

I've heard good things about the vacuum-cooling-system fill tools, in terms of eliminating air pockets.

www.amazon.com/MASTERCOOL-43013-Vacuum- ... YS2JJTRJNV

https://www.amazon.com/Airlift-Cooling- ... YS2JJTRJNV
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