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We are on our SECOND 2008 Uplander, and both have had the same exact problem.
While idling, the heater will not blow heat. Once you touch the accelerator and rev the engine, heat will flow... upon releasing the accelerator, the air will slowly cool after about 30 seconds, and after about a minute, it will blow continuous cold air until you hit the accelerator again.
The problem seems to be intermittent.
The thermostat has been changed, the coolant has been flushed and all air has been removed from the lines, the water pump has been changed and nothing has fixed the problem. The dealership identified the problem and agrees that it is an issue, and says that all fixes provided by the manufacturer have not worked, so they gave us an entirely different vehicle with LESS mileage, and it worked ok for about a week... it now has the SAME exact problem.
After doing some research online, I have found several other people with the same issue... has anyone found a fix for this? Does anyone here have a similar problem?
We do NOT want to go through the hassle of having to get into another vehicle, and would prefer it if the problem would just be fixed. We live in North Dakota and have a baby, so you can understand that not having any heat in our vehicle is a very important issue to us... especially in -20° to -40° degree weather.
If anyone can help or offer any additional information on this, I would greatly appreciate it!
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I don't believe my 2008 LS with 37k has that problem. I've had the vehicle since January here in Washington State and would have noticed if it had occurred, although your extreme cold might have been a factor. .
Is your engine temperature indication normal? Does it vary sporadically also? I would still wonder if air is getting into the system and migrating into the heater core at low RPM. Or if some kind of an internal valve is blocking the coolant flow through the core when idling. It is conceivable that there is a servo-operated valve although I haven't looked it up. Since the problem has occurred on multiple vehicles it would be interesting to know if a certain production run was involved. I hope you get a resolution. Is this still happening now that the weather is a little warmer?
EDIT: I found this on another forum from ND. Is this you?
"When the car is idling, the heater switches from inside heated air to outside vented air. The switch happens around 1700 rpm. This can be a problem when it's -25 degrees and you stop at a light(yikes). The manual says that the outside venting should be shut off if it's below a certain temp."
I also found that post on another forum while doing searches... no, it isn't me. I only posted the question one other time at 2carpros.com, and it was pretty much identical to the post I made here.
Doing searches, I found several other people with similar problems... and, to be honest, it's a bit disconcerting.
The engine temp seems to be normal... it peaks at a hair above the 50% mark. It does seem as though the vehicle takes forever to warm up, as I've left it running for 30 minutes and the temp gauge never seemed to get past the 30% mark. It will eventually reach normal levels, but only after driving it.
Now that the weather is a tad warmer, the problem is definitely harder to identify, and seemed to disappear completely once again the other night.
We were in contact with the dealership again, and they think they might have a fix for the problem this time... a new head gasket and bolts? Seems like a pretty extreme fix, but if it works, that's all we care about right now.
I just bought a 2009 uplander ,oonly 4000km and started expiriencing the exact same problem!!no heat at idle!as soon as the engine revs past 1700 rpm it blows hot.most likely a vacum controlled valve. at idle vacum drops.
If the hoses going to the heater core are hot, and I assume they are considering all you've done, the problem is most likely with the HVAC system under the dashboard. The air temperature is controlled by a door, or flap, which moves (or should) according to where you set the temperature control. When you ask for warm air, the door directs air through the heater core. When you want cool air the air flows through the AC evaporator.
The device that moves the temperature door is often vacuum controlled. Engines at idle produce high vacuum. Engines at part or full throttle produce less vacuum, so if there is a leak in the system somewhere, the door can move on its own, depending on engine speed, causing exactly the symptoms you describe.
I'd start looking for a vacuum leak in the hoses or the vacuum devices under the dash. This is a very common problem. You may even be able to see or hear the temp door moving if you crawl down in the passenger footwell and do some experimenting with the throttle. NOT while you are driving, please. By the way, a service manual, such as Haynes, can be very helpful in diagnosing something like this.
Finally they fixed the problem and it has worked fine since.they installed an inline water booster pump. It was gm's grant motors in vegreville alberta.i had to be persistant,but finally the engineers of gm recognized it has a problem.
I am in South Carolina with a 2008 Uplander w/65000 miles and it started having this problem last month. My question is: did your dealership fix this under warranty or at your cost? If at your cost, what was the cost (if you don't mind me asking)?
I am learning this is a very common problem. We bought our 2006 Uplander from a dealer in Milwaukee after GM repaired the vehicle for a heater problem and put a bumper to bumper warranty on it for a year. It has been in the shop now three times for heat problems, each time a little different but with no resolve and the dealers having to call GM for help.
The first problem was fixed they said when they installed the booster pump, that worked for about three months and then you wouldn't have any heat if you went faster than 45 miles an hour.
The next time, they removed the booster pump and put in a diversion bypass valve and then after a couple of days you didn't get heat at idle, and only get heat when accellerating.
Now the blower stays on for about ten seconds after removing the keys and whenever you let off the gas the fan acts like it is going to stall out and the headlights dim, then you lose heat.
I can't believe no one can seem to fix this problem, but I have trusted my dealer locally for many years with no problems and they seem lost at this point.
Ironically there is no Haynes or Chiltons repair manuals for Uplanders and am wondering if anyone has found a resolve that lasted longer than a year