JPod

Hello to all,

I am totally new to this forum so please forgive any noob faux pas that I may commit. I have searched through numerous threads on this topic unfortunately nothing has seemed to do the trick so I thought I would post a new thread with my specifics.

Our 1999 Tahoe (5.7L) is not creating hot/warm air. So far this is what I have done: I have replaced the thermostat, this did fix an issue of getting really hot then cooling way down, the gauge would read around 150 then jump to 230 then right back down to 150, now it holds at around 155 or so, though I know this is not completely accurate since it is a 195 degree thermostat but at least I am not concerned every time I see it spike. I think there may be a coolant leak in the system but it is not enough to note where it may be coming from and I am not seeing significant loss so it may simply be normal evaporation.

I have done everything I know to purge the system of air including multiple cool down/heat up cycles filling as needed and keeping the overflow filled. I have also parked on a very steep incline to get the radiator cap above all areas to 'burp' the system. I have replaced the heater control valve which was a source of a significant leak a while back.

I recently replaced the blower control because the fan was not working, as well as the blower motor resistor. When I change the temperature gauge inside the vehicle I hear a change in the airflow so I know the servo that controls the air flow door is working.

When I run the truck for a while I start to get a small amount of luke warm air that comes out of the vents but it is by no means the hot air that should be coming out.

One other note, when I used to drive the truck and accelerate I would hear 'bubbling' come from the heater core, this was prior to changing the heater control valve which I attribute to air getting in the system. Now I do not hear any fluid 'bubbling' in the heater core.

I have also checked to see if the heater core hoses (the two that come off the control valve and go into the firewall) and note they are warm to hot after running for a while, this is to say they are quite warm but not so much that I cannot hold on to them for any length of time.

Please help, this is my wife's vehicle so her and my 3 year old son are starting to complain about being cold as the temperature is now dipping into the low 30's in Seattle.

JP

kevinkpk

I'd revisit the heater control valve, is it really working, hooked up correctley?

JPod

Near as I can tell it is hooked up correctly. I put the new one in the same way as the old one came out. It is a 4 hose manifold with a small vacuum line. I take the vacuum line off and I do note there is no vacuum though the hose is in good order, not sure if it only draws vacuum at specific times (heat on high or cool).

kevinkpk

Rereading your post, you say you replaced the tsat since it wasn't maintaining a constant temp, and I read the new one isn't holding a 195? I'd replace the tstat again.

JPod

Please bear in mind I am basing temp on the dash cluster temp... I have owned a 96, 98, and 99 Tahoe and every one of them registered around 155 on the gauge (about half way between the 100 and 210 marks), the coolant is certainly hotter in the system, I was stating this so there would not be questions regarding the thermostat.

in2pro

Welcome to the forum , the heater core my be clogged and only getting limited flow resulting in the minimal heating.

JPod

What would be the suggestion for unclogging the core? The heater core was replaced prior to us buying the Tahoe a little over 3 years ago, we have logged maybe 35-40k miles since we have owned it. Can I flush it with water or pressurized air? If I can do this is it possible to do while still in the vehicle? Also is it possible that there is an air lock of some sort or is that unlikely?

in2pro

What does the inside of the radiator look like when you remove the cap? Reason I ask is if the coolant was mixed with different types it will create a cheese like gunk that can clog the tubes...
Yes you can try flushing it by removing the heater hoses, you will probably have better luck with using water then compressed air...
Is it possible that it still has bubbles.. yes but it sounds like you have done everything to purge it...

JPod

It will be a couple days before I can get under the hood and work on it again, I will update everyone this weekend.

JPod

Well I got under the hood and did some work, ended up replacing the heater core and low and behold we have heat...and a new problem...

I am not sure if I should start a new thread but I will put it in here and if a moderator moves it so be it

I know I have some issues internally with the motor (pushing 200k miles) but it started a new trick today. I pulled the oil fill cap while the motor was running and the idle went way down and the vacuum was VERY strong, it felt like a high HP shop vac. There is also foamy spoom in there...telltale sign of water in the oil (crap), I have also developed a misfire, I am thinking that I will be replacing the engine in the next month when I get my tax return, likely less costly than rebuilding the existing one, I have found a couple locally for around $800.

My question is this, is there any reason that I should be worried about the engine blowing up on me while doing short drives around town if it seems to be keeping normal oil pressure and water temps?