Chevy & GMC Vans

I've had this '95 for about a month now, during which there have been some cool mornings. Heater/defrost seemed okay, but now that it's cold, I find that I'm blowing cool air-just slightly warmer than straight vent. Where should I start? +oM

make sure your heater core has not been bypassed.

Make sure you have a full helping of antifreeze. I've had "cold" heat in mine before and damned if it wasn't due to being low on antifreeze. The van never ran hot, but apparently the lack of antifreeze let air get in the heater lines and I lost heat. It took several fills to get the air burped out, but I never did anything more than fill it and drive it to fix it.

Hope your problem is that simple.

Yeah Matt I hope it's that simple too! I didn't even touch the truck today. My wife had surgery, and besides, it's fuggin cold out there.

An off-my-own-topic note to Justice-either here or on the mother board, I saw your stack of basswise gear. If I ever get caught up on shite and properly camerad, Iwill post my rig..........+oM

On further review, when van is in motion...as in driving down the road, blows pretty good heat, at least on defrost setting. Set it in park and the temp just starts to drop, until it feels like ambient air temp. WTF?

How does the engine temp compare between when you are driving and when you are parked?

Have you checked the bypass. I'm sure someone will correct me, but I seem to remember it runs on vacuum and it may be that you are not getting enough when you are idling as opposed to driving. Of course I could be all wrong on that as I have never looked at mine.

tomdad wrote:On further review, when van is in motion...as in driving down the road, blows pretty good heat, at least on defrost setting. Set it in park and the temp just starts to drop, until it feels like ambient air temp. WTF?

Hmm, could also be a thermostat stuck in the open position.... Is the temp gauge reading cooler than normal?

.......alright, did a good bit of driving this morning, and quite simply, when the van is in motion, good heat thru vents, defrost, whatever. When waiting at red light or parked in 'park', back to the cool stuff. BTW, previous owner had water pump and thermostat replaced this past summer.

+oM

If heater bypass is in down position when heat is engaged...and up position when not, does this indicate this valve is operating properly?

Is your coolant just low? That is what it sounds like.
Having low coolant will cause the problem you are describing - more heat while driving & no heat while idling.
Having a faulty thermostat will cause the opposite - no (low) heat while driving & more heat while idling.

Bypass is down when heating, up when not. So, yours seems to be operating properly.

Well lesee......bypass seems to work, coolant was added, no difference, hoses to heater core are hot, and still warm air only at higher rpms. So this leaves what, blocked up core?

Well, since so many of you offered ideas on this, and since due to a family situation or three, it took me so long to finally get it done, I wanna tell y'all that it ended up being a partially blocked heater core. Some back-flushing did the trick.

Thnx.....+oM

Uh-oh, this thread about the heater has given my Astro ideas on how to get more attention from me...there's a slight smell of antifreeze whenever I turn on the heat or the defroster. It isn't to the point of filming over the windshield or leaking on the floor, but I know it won't be long.

The previous owner had replaced the heater core a year or two before I got the van, so that means the core is around 5 years old. Seems like a short lifespan to me, but I did install a Stewart high volume water pump when I did the V8 swap. I've since read that these pumps can overwhelm an aftermarket heater core with the increase in flow and cause leakage a lot earlier than would an OEM water pump. The fix is to install a GM heater core--supposedly they are better built than the aftermarket ones.