98 Blazer Heating problems

4.3L 165k:

Over the weekend I replaced the thermostat in my ride. I checked out this forum ahead of time and looked over a few previous threads and I decided thats what I needed to do.

Before, teh engine was running at the mark exactly halfway between the 100 degree mark and the 210 mark. I replaced it with Duralast thermostat and when I took her around the block the needle went up to the tick just below 210 and was giving me heat. Well, the rest of the week was pretty warm here in Indy till last night. Thats when I discoverd that now I am getting only cold air and the needle has dropped just a hair under that tick.

About 3.5 years ago my radiator was replaced when they replaced my transmission. The torgue convertor was rusted out and they thought maybe the intercooler had leaked coolant into the tranny...

If anyone has any ideas or a specific forum where this issue was addressed already, (I couldnt find it) I'd really appreciate the help.

While the engine is running at operating temperature, check both hoses at the heater core. They should be hot to the touch, with very little temperature difference between them. Post your findings.

Yeah, Thanksgiving night my brother and law looked at it with me. We topped off the fluids, and let it idle up to operating temps, it got warm, but not very. We checked the hoses going into and out of the heater core and they were both rather warm. The one to the left seemed like it was hotter than the hose on the right, but it didnt seem like by too much.

I noticed yesterday when I left for work it was giving me luke warm heat; (It is stored in my garage at night) when I left the jobsite after it had sat for about seven hours, in the cold, and got on the freeway to come home, it didnt give me any heat the entire way home. My Pops has a valve that we can hook a garden hose to and attach it to the heater hose to flush out the core. Should we try that?

Thanks O' Master.

Flushing the core can't hurt, just don't put too much pressure on it, they're pretty fragile, ...and time consuming to replace.

The 98 has one temp sensor and the PCM uses that signal for engine controls and also sends a signal to the dash gauge through class 2 communications...The dash gauge should hang around 200 degrees, an OBDII scan tool will tell you exactly what the coolant sensor is sensing. The upper radiator hose and the heater hoses should all be close to the same temperature as well.

Ok I'll remember to keep the pressure low when we flush it out. If that fails, do you have any other suggstions? Would the core need replacing? Should I replace the cap on the radiator? I'm pretty sure they re-used the old radiator cap when they replaced my original radiator. Not sure how to test the cap, it seems to be holding pressure, but I'm not the expert. ;)

As for the upper radiator hose; which is the one that goes into the engine where the thermostat is, correct? it seems to be pretty warm as well, maybe a bit hotter than the heater hoses...I will check tommorow after I get home, and get back to you then.

Gracias

De nada. It is possible the core has a build up of scale that flushing will not remove. If that's the case, replacement is the only repair.

Radiator caps are cheap, easiest to replace it to be sure that's not the problem.

The upper radiator hose goes from the thermostat housing to the radiator.

The upper radiator hose is hot.

The heater hose on the left is as hot as UR hose

The heater hose on the right, goin out of core??? Is only warm to the touch.

in-dash temp. reading is in the 180-85 range

Might be two problems going on here. First: 180 to 185 is too low, should be minimum 195 degrees, that's when the thermostat begins to open. Check engine coolant temperature on a scan tool and if possible, use an infra-red temp sensor on the upper radiator hose where it connects to the thermostat housing. This will give two temps to compare, both readings should be nearly identical with the engine running. Second: The heater core may be restricted or have an air pocket, if both hoses are noticeably different in temperature.

Both heater hoses are noticeably different to the touch. Did I create an air pocket when I replaced the thermostat? How do i fix that problem?

Also, I dont have an infra red sensor, I'll ask around and see if I can borrow one if you think its a must...

Thanks again

Any time the cooling system is drained, the possibility of an air pocket is real. Check in the "How To" section in the Blazer forum, there are several threads that tell how to "burp" the cooling system.

The only reason you would need the infra-red thermometer would be to confirm what the ECT sensor is sending to the ECM. At the least you should check coolant temperature with a scan tool.