Chevy/GMC question??

[jmvotto]

For you mechanical guys.

I have a 2007 chevy suburban LTZ, the heater works great but does not blow warm air until it is under motion. it can sit in the drive for 30 minutes temp at 210 fan blowing, but only cold air, get to the end of my street and it is now its warm???????

[mmandley]

Yea first thing is when you are in the truck does the temp gauge read normal?

Sounds like maybe only a couple items here.

My first thought is when you come home at night and park the truck that blower box is nice and warm from the trip home. You have to remember whether you use the heater or not. The heater in the truck is always on. Theres a door in there controlled with vacuum normally or a little electric solenoid that move a door from the heat side to the AC side.

I think when you get home and the truck is cooling down that condensation might be building up in there and the door is freezing or sticking on the cold side. When you actually start to drive the increase in pressure threw the heating system as the engine revs up creates enough stagnant heat to free up the door.

Another option is the solenoid might be sticking, or if yours is still a vacuum there might be something wrong with that part of the system. Cant you or have you tried moving the heat from the dash to the floor settings to see if you get heat that way?

You might also try just moving the temp gauge from hot to cold and back to see if that works, they will cause that door in the air box to move.

I know on my F150 last year it would get real pissy sometimes and give me no AC the blower was on and everything seemed like it was working but no AC. I had to turn the ac off a couple times and then all the sudden a rush of cold air would blow out. Always made me panic a little as it was always on the hottest days up here and on my way to lake so there was no way i wasn't going to the lake LOL.

[kaneboats]

Could be theromostat stuck open-- or going bad but not all the way yet. Low coolant level can cause this too.

[sailing217]

yep. replace the thermostat

[brain_rinse]

I love playing armchair mechanic! I think everyone else beat me to the punch though. I agree, coolant level, thermostat, and blend door in that order.

[kaneboats]

Or it could be so friggin cold outside that until you are under load there's just not enough heat developing to open the thermostat. If it was a 180 it would open but a 210 maybe not if you're just sitting there at idle. Try idling with the truck in gear so there's some load on the engine and see if you get heat.

[mmandley]

I can agree with low coolant as a consideration.

Stuck T stat nope cant agree on that only because if he has 210 then the T stat is open or the engine would over heat already.

If the T stat is stuck open he likely wouldn't be able to warm the truck up to 210 with out driving.

Eighter way a 210 T stat in a gas engine is pretty dam warm LOL. Most gas engines over heat at 230 to 240 but then again you are in snow country..

I think if it was my truck though i would replace the T stats to rule it out as its a cheapy part and then fill with coolant and make sure theres no air because that can give you a high temp reading and the truck is still running cold due to steam buildup at the stat.

[jmvotto]

Thanks for all the responses. I will check the coolant level seams like the easiest option. Have no idea wear the T stat is, have to check the manual...LOL I guess i should not have opted for Home Ec in school over auto class, but i like to eat....:D

[maxpower220]

More info is needed. Do you have automatic climate control in the truck? When you are starting in the morning (assuming this is the only time it happens), how do you have the temperature control set in the truck (auto hot at 80, recirculate/outside air, etc). You mention the fan being on, what level, low/high? Do you have rear heat and what is it doing, what is it set to?

Based on the random info provided, I would say you have an issue with your temp control module. Has this happened just once or an everyday occurance?

[kaneboats]

That's not why I was in home ec. :D

Here's a start:

http://www.ehow.com/how_6369094_replace-thermostat-suburban-2500.html

[mmandley]

Thanks for all the responses. I will check the coolant level seams like the easiest option. Have no idea wear the T stat is, have to check the manual...LOL I guess i should not have opted for Home Ec in school over auto class, but i like to eat....:D

1st open hood and at the Radiator follow the upper hose back to the engine. 90% of the time its a round housing and thats the T state.

T stat job is to Stop coolant from the engine coming into the radiator. This way the engine will run hot and warm up the coolant inside it. The hose at the bottom of the radiator is the cold inlet from the radiator from the engine. This way hot fluid enters top of radiator and is cooled as it flows down.

The way the system works when the T stat is closed is theres an extra port on the water pump and you will see 2 hoses from there to the firewall. This is the heater hoses and this is also why the heater in your truck will heat up before the T Stat opens.

If you ever blow the heater core in your truck a fast temp fix is cut the hoses at the fire wall and connect them with a junction tube and it will act as a loop till you replace the heater core.

[jmvotto]

More info is needed. Do you have automatic climate control in the truck? When you are starting in the morning (assuming this is the only time it happens), how do you have the temperature control set in the truck (auto hot at 80, recirculate/outside air, etc). You mention the fan being on, what level, low/high? Do you have rear heat and what is it doing, what is it set to?

Based on the random info provided, I would say you have an issue with your temp control module. Has this happened just once or an everyday occurance?

Max. Evey day occurrence. Settings on high 80+, fan high, circa or non circa. Either way no heat until it moves.

[jmvotto]

Ding, ding, ding, ding, ding. Winner winner chicken dinner!!!!

Coolant level was low, but not low enough to trigger the sensor, strange.

Thanks, now I know where the t stat thingy is:D

[kaneboats]

Glad to hear we could help. Also glad you have no serious issue, other than the fact you are losing coolant somewhere.

[in the bubble]

It's most likely yur blower mode actuator located in center of dash buy the center tunnel or hump. They go bad all the time. If you had a Tech2 scan tool then you can reset all actuators. And see if it goes from cold to hot to cold again. This is a know problem with Gm trucks for about 10 years now. I never seen a T/stat stick open on this motor. If it did it would set a code for low coolant temp. The water pump gaskets do go bad before the waterpump does. But everyone will sell you a new pump.

Gmt service tech since 1986. And Graduated to Toyota in 2009.

Mark