lohman, other mechanics

[thecavemankevin]

The heat in my 03 grand caravan is acting odd. It will only work when driving/engine is around 1800 or so. Even if the van is well warmed up, but i stop at a light it will then blow cold air. I have topped off the engine coolant, pulled the hoses off the heater box and blasted that out with a water hose to make sure there are no clogs in it. I know it is not the fan because it will blow air at all speeds no problem. I was wondering if it could be the thermostat wrongfully closing unless the engine is above idle. The water temp is also in the norm at all times when running, so it is not overheating or anything.

any ideas?

[kevdupuis]

I'd check for vacum leaks to the controls and heater box since you said the coolant level is fine. There might be a leak in a line or actuator allowing a door to divert air flow through the vent side of the system at idle.

[Lohman446]

Coolant level is the first issue to check for, which you said you did, make sure you do check it in the radiator (NOT HOT) and not just hte overflow as sometimes the overflow theory does not work well and you can be low on coolant even though there is coolant in the overflow - stupid but true. This is the normal cause of poor heat sometimes, especially coming and going dependant on engine speed.

You may be on teh right track though on flushing things - a restricted coolant system will cause poor heat at lower RPMs and better heat at higher RPMs. It may be worth flushing the entire cooling system a couple times.

The other surprisingly common issue I have seen cause this is the fins on the water pump being rotted off / pulley broken etc. There are of course other causes but those are the first few things I would look at.

I doubt its a thermostat, however they are so cheap it is worth trying, if you're mechanically inclined enough to flush the heater core your fully capable of changing the thermostat, and thats the cheapest guess, even if a poor guess.

[billybob_81067]

I would vote for the vaccum leak theory... high vaccum at idle causing the blend door to pull to the cold side maybe? The blend control might have a leak in it...

Just put on a coat ya sissy! :p

Edit: Also, does it get cold right away after you let off the fuel or does it take a little while? If it's instant then I'd bet money it'd be the blend door, but if it takes a little while then it would more likely be the coolant not pumping through the heater core which would still be hot for a little while before it cooled off.

[Altimas]

I had this same exact problem with a truck I owned and my problem was a Vacuum leak, so definately check that out.

[thecavemankevin]

I would vote for the vaccum leak theory... high vaccum at idle causing the blend door to pull to the cold side maybe? The blend control might have a leak in it...

Just put on a coat ya sissy! :p

Edit: Also, does it get cold right away after you let off the fuel or does it take a little while? If it's instant then I'd bet money it'd be the blend door, but if it takes a little while then it would more likely be the coolant not pumping through the heater core which would still be hot for a little while before it cooled off.

no, it dies off pretty quick so you guys may be onto something. only problem now is finding out where on this van the blend door is. i've never dived that deep into climate controls.


I'm good with older vehicles (i can tear apart and rebuild a VW bug myself inside a weekend but these computer driven cars are a little above my learned curve. Other than buying a Chilton/Haynes manual any suggestions where i can get detailed info (on the net) on the blend door/vacuum hookups?


ps: my wife is the one whineing about the temp, i told her the same thing and got a real dirty look....along with the "if you only listened to me and took it into the shop when i told you something was wrong......" Loh, you should enjoy the fact you're single ;)

[Lohman446]

You don't want to get too deep into the heater box on that vehicle, most Chryslers it involves removal of the dash and becomes a pretty healthy job. Easiest way to check vacuum leaks is get hold of carb cleaner, spray the vacuum lines under the hood, around the base of intake, if you change the idle you have a vacuum leak.

[thecavemankevin]

You don't want to get too deep into the heater box on that vehicle, most Chryslers it involves removal of the dash and becomes a pretty healthy job. Easiest way to check vacuum leaks is get hold of carb cleaner, spray the vacuum lines under the hood, around the base of intake, if you change the idle you have a vacuum leak.

So i guess the blend door is in the dash huh? Thats what i was afraid of. good thing i bought the extended warranty. It has already paid for itself when the computer had to be replaced.

When spraying the vacuum hoses with carb cleaner, i assume the idle should increase if there is a leak?

[Lohman446]

So i guess the blend door is in the dash huh? Thats what i was afraid of. good thing i bought the extended warranty. It has already paid for itself when the computer had to be replaced.

When spraying the vacuum hoses with carb cleaner, i assume the idle should increase if there is a leak?

Yep

[PyRo]

When spraying the vacuum hoses with carb cleaner, i assume the idle should increase if there is a leak?
Could make it stutter or outright die also.

[Lohman446]

Could make it stutter or outright die also.

Pyro's right on that, any change would indicate a leak - the sensor systems can throw it off from doing what you would expect. I did bother to check TSBs and recalls and there is nothing related that I found. Good luck :)

[thecavemankevin]

thanx guys, i'll let yall know how it does