I have a 95 Suburban that blows cold air. (350 5.7 engine) I suspected low coolant level & found that my radiator wasn't 100% full & my water pump had a small leak. I replaced the water pump, both upper & lower hoses & the tstat (195 degrees) After the repairs the temp gage on the dash varies between 175-210 & the air from the vents is only slightly warm. 95-100 degrees. Is a 195 tstat the correct temperature? Could there still be an air pocket somewhere? How can I troubleshoot this further? The controls all seem to be working properly. What else can I check or verify? Thanks in advance,
Benjamin

 

When refilling the coolant, you did run engine & your heater at same time correct? I usually do that with cap off, and watch coolant circulate through rad 3 or 4 times, as well as rev engine slightly from time to time, to give that little extra push through heater core. Checked for vacuum lines knocked off during repairs ?

 

I would suspect air. You can try parking it on as steep an uphill incline as you can find, remove the radiator cap (cool) and then start and let idle until the thermostat opens. This will often "burp" an air pocket. As the engine warms up you will get some overflow out the filler neck as the coolant heats and expands. When the thermostat opens you should get a sudden drop in the level, the upper hose will get hot, and you will see circulation of the coolant. Give it a minute to expell any air, then top off the radiator and put the cap on. Your 198 stat should be correct.

 

Thanks for the replies Tow Guy & Mike. I did have the cap off while I ran the engine & waited for the tstat to open once. I verified that the upper rad. hose got hot. When the radiator started to overflow I put the cap back on because I was also checking for any drips/leaks from my repairs. I may
not have run it it long enough or through enough cycles to removed the air or "burp" it.
I'll try parking it on an incline and letting it run through a few cycles while reving the engine ocasionally.
I'll post the results.
Benjamin

 

OK, I placed the car on some ramps to raise the front end & removed the cap. I then ran the car for well over 30 minutes watching the coolant circulate, verifying the tstat opened & the upper rad. hose got hot. I turned on both heaters (front & rear) & revved the engine. I watched the temp gage vary between 150 - 210 max. I could see the fluid over-flow from the radiator at least 5-6 times. I topped off the coolant level & re-installed the cap. No improvement. I borrowed one of them laser thermometers & recorded a discharge air temperarture of only 70 F max from the vents. I used the laser thermometer under the hood & got 180-200 F at the tstat location. The lower rad hose was around 90 F. The top of the water pump has a heater hose that goes into a splitter type manifold (3 hose fittings) where 1 hose comes from te water pump, 1 hose goes to the back of the engine (rear of intake manifold? & 1 hose looks like it goes into the firewall. Where is the heater valve located, under the dash? Is there is a single heater valve that allows hot water into both the front & rear heating coils? Any suggestions as to how to troubleshoot this issue further?

 

ben
try to take the heater hoses off at the firewall and flush out your heater core both ways to make sure flow is ok.. then flush thru lines that go to your rear heat, there is a heater core back there also. you dont have to but i recommend a spill free burping funnel, kinda like parking it on the hill but this funnel lets the coolant stay at its highest point and easy to watch. then when filling up leave your heater hoses off until you get coolant to pour out then hook it up.
hopefully this helps
tony22

 

If what TG says doesn't give what you want, remove the outlet hose from the heater core, remove the output hose from the block, put a garden hose on the output hose and backflush the heater core. If someone has used Stop Leak, etc. then it usually settles in the heater core. I had to do this for about 3 winters in my 93 K1500.

 

Larry, from the reports I am hearing, it sounds like you guys might actually need heat down there by you.

 

Last week, yeah. 14, 5, 11 degrees. Finally warmed up today, and should stay nice for a few more. Maybe I can get some work done, now. Can't even straighten out an air hose at 5 degrees without it breaking!

 

Are you certain that the blend air door is switching fully? You could have lost vaccuum to your blend air door actuator, or the actuator itself could be bad, or something (a pen is common) could have fallen into the vents and is jammed into your blend air door, or your blend air door itself could be broken and not switching fully.

It sounds to me like you have followed correct procedure for bleeding the air out of the cooling system and based on the temperatures and symptoms you have given it also sounds like your thermostat is working correctly....I don't think that is your problem.

It could very well be a stopped up heater core, but if I were you I would verify proper operation of the blend air door first because you can do it INSIDE the vehicle and it is alot easier than jerking all those heater hoses off that god-forsaken firewall.

Let me know what you come up with in either case.

 

If you have a gun for temperature sensing/reading, aim it at the heater hoses, top & bottom where they enter the firewall, while running the engine and heater at normal operating temperature. Record both hose temperatures and see if there is much of a difference. A big difference at one compared to the other, would indicate low or no flow through the core. Actually that gun will help you find the problem area pretty fast I would think, just by following each hose and watch for large change in temperature, which would isolate your blockage, if blockage is the problem. If it's a blend air door problem as stated in other reply, you should record fairly close temperature from both in & out of heater core.

 

These guys have some great advice, never heard of having air bubble in coolent system though, If you are not getting heat I think these guys are right on the money about back flushing the heater core, you can take the core out and do it but, I believe that you have to remove most of your dash. I need to do the same thing, I am glad to have seen these messages because I was gonna remove the core, which would most likely have made me say f it toss the car,,, I used CLR (buy it in any hardware store to backflush my coil in my boiler for hot water and it worked better than I could have imagined!! The guys are right, have to flush it out backwards preferably with CLR and HOT water, if you can put the stuff in and then let it sit for an hour, then use a air compressor (gently, not sure how fragile these things are) you should cover the other side with a rag so you dont get it in the face, and you will not believe the junk that comes out. Then do it again a few times till it is clear and air and water comes out easily(make sure you have the heater switch on full hot, without the car running obviously. see what happens, I am going to try it later today, thanks guys about the idea of going thru the firewall, sometimes it is the most obvious things that dope slap you into NOT doing something you were going to do!

 

The heater core is not all that fragile unless it is corroded and/or cracked and weak in a spot. The working pressure of cooling system is about 16psi so the heater core is designed to withstand that much pressure easily. The main thing about using an air compressor is to make sure the air can flow freely through the heater core before you blow into it full blast with your air hose. Most compressors will put out 90psi or more and so if there is a block in your heater core that does not allow the air to go THROUGH then that much pressure will build up VERY quickly and you will end up most definitely with a leaking heater core. Personally, just to be on the safe side, I would recommend the water only. Another thing you can do to determine if there is blockage is to take the heater hoses off one at a time and then crank or briefly start the engine. One hose should have coolant coming OUT of it and into the heater core at a pretty good clip, the other may have a slight dribble but nothing more. With the OUTPUT hose hooked onto the heater core and the other hose clamped off you can start the engine and see how well the water/coolant flows through the heater core. THis will also help you determine which way the coolant is supposed to flow for "backflushing" purposes because it is not always clear.

Also, if you are flushing the core AT the firewall it will make no difference whatsoever what position the heater switch is on while you do it. The heater switch controls the blend air door and (on some vehicles) a heater control valve. THe heater control valve is usually inline with one of the heater hoses and blocks off water to the heater core when shut. If your vehicle has one of these you need to check and make sure it is operating properly before you do anything else because if it is not it could be causeing your whole problem to begin with.

 

Thanks for all of the help & advise guys. I now hAve in in both front & rear heaters. I went to the local auto store & purchased 6 feet of heater hose & cut it in 1/2 so I had 2 each 3 foot lengths.
I gained access to the 2 each spliter manifolds (1 for the front & 1 for the rear) . I then disconected all lines & connected a section of the new heater hose to the heater cores & flushed them in both directions. I used a barbed X female hose bib fitting that goes inside the heater hose. The fluid/coolant looked normal when I flushed in the "normal" direction but some brown water & bits of rust came out when I reversed flow or backflushed the coil. Thanks again for the help, it's nice to hace heat again!
Benjamin

 

glad to hear everything worked out for you. If you have problems again what you might consider doing is swapping the hoses on the heater core nipples which will effectively reverse the flow of the coolant throught the core. I have done that one a few of my vehicles and it helps prevent future clogs.

 

So I take it that at the time of the flushing you probably thought there was no way the flushing procedure was doing you any good?, based on the little amount of stuff that came out? Is that a fair presumption? But then you had real good heat afterwards?

I am curious based on the amount of stuff that you got out if that was really your problem or if there was some air bubble caught up inside. If not, it is interesting to know that positive results can be had even if just a little brown and rust comes out.

 

When I had to back flush mine, gobs of white "stuff" came out, which I assumed to be stop leak or some other chemical the dip wad put in the radiator to try and fix it before I bought it. It wasn't rust, but little curly balls of crud. Had to do it for 3 heating seasons before it finally all went away.