I am having another issue with my Chevy Venture 98' heater.

When I turn on fan it starts out hot, but then fades out, If I leave it on 1st or 2nd gear it still blows hot, but as I turn 3-5 gear on, it loses heat, it turns into warm air, it might even not be warm.... If I turn it off, wait and turn it back on it will blow hot for a few moments...

Do you have any ideas what can cause this?

I just replaced radiator cap, thinking that it might help - it didn't...

Head gasket has been changed recently - driven 20 000 km (12 000 miles) since. Doesn't seem to have any issues with engine getting hot or loosing excessive amounts of oil/coolant. Don't get misfires. Engine seems to be running fine...

 

I suggest you to check the radiator fluid. If it is low, get it vacuumed and top it off. You may have anything from a blockage in the coolant system, like a leak or an air lock. If the coolant system gets vacuumed down you can find whether there is a leak or an air lock. Furthermore, try to flush the coolant system, if it not works you need to replace your heater core.

 

If it has a fail safe thermostst I'd suggest replace it. My lumina last winter barley at times put out warm air due to that.

 

The heater core could also be partially blocked. Mine was totally blocked and I removed both heater hose on one end away from the core and flushed it out. Put on new hoses and now plenty of heat.

 

Thanks for a valuable suggestions - will try to figure out how to flush heater core.

And I have bought thermostat already - so that will get changed as well.

 

It's all bad... My Chevy is giving me a grief...

Looked today at my oil dipstick and oil color was milky... Taking off the oil cap - same thing...

Obliviously coolant is mixing with oil somewhere... Now it's only matter of taking everything a part (again) and fining where... Perhaps it's not head gasket, but lower intake manifold gasket ?!

Let's hope for the best and prepare for the ... $%#@

 

Wanted to give a quick update on progress - changed Lower Intake Manifold Gasket over weekend, despite the fact it was Fel-Pro and it was only about 9 months old it was blown... Changed it to a better Fel-Pro gasket (with metal base instead of plastic) and now it appears to be working fine - no oil and coolant mix....

Of course it didn't solve issues that I had with heating, so got the front and rear (this was ok before) heater cores flushed and now it's blowing heat as crazy. It didn't appear to flush a lot of "stuff" out from heater core, but I guess that was enough to make it work like a new again.

Also I noticed that my engine temperature is much lower and more stable while idling after flushing heater core. GREAT!

Thank you oldchevy, Jeff Collision and kevinkpk for suggestions!

Cheers!

 

I think I know which ones to flush but want to be sure before I ruin my father in laws van. We want to try this before replacing but im not 100% sure. The two hoses I thought were going in and out of the core were both hot so it doesn't seem like its clogged because shouldn't one be hot and one not?