What if the thermostat is stuck in the open position?

Does your blower motor work?

When was the coolant system last serviced?

My advice:

drain it, flush it, new thermostat, fill it & new radiator cap.

If your blower motor isn't working, then the owners manual or a Google search will tell you what fuse to look at.

Hope that helps!

 

Yes, the blower motor is working fine. Not sure when the coolant system was last serviced, but I checked in the radiator and it's full. Not sure on the thermostat, will have to look there. Wouldn't the engine be overheating though if the thermostat was stuck?


One thing I haven't tried is bleeding air from the coolant system. However, to do this, do I just open the radiator, then turn on the engine and let it reach operating temperature, and see if the coolant level goes down and air bubbles come up? Or is it not safe to let the engine heat up with the radiator cap off? (I know that if the engine is operating and the radiator cap is on, you do NOT take it off as it will spray out hot steam and coolant).

 

If the blower motor is working, it's not electrical.

If you haven't been monkeying around with the cooling system, and the radiator is full, I doubt there is air in there. You can search the forum for "burping" the coolant system...

If the thermostat is stuck in a closed position, not allowing the coolant to circulate, then yes the engine is more likely to overheat. If the thermostat is stuck in an open position, the coolant circulates once the vehicle is started and it can take forever to warm up. Thus no heat for a long long time. This is especially true when it is cold outside.

To check the thermostat, you are going to have to drain some coolant. Not knowing the maintenance history you may as well do a flush and replace the thermostat and the radiator cap. You may even have to flush it more than once. After you get it all back together and filled up, I would pressure test the system cold and check for leaks. It is possible after flushing the system to develop a leak.

To drain the coolant system, don't mess around with the dinky drain on the radiator, just remove the lower radiator hose.

Hope that helps!

 

Thanks for the information, it is much appreciated It might be a little over my head though. I'll have to see though as there is a video on Youtube of how to do a coolant flush of a Chevy Blazer 4.3 L so I'll have to watch it first. I do believe that there is a very slow coolant leak, as I keep having to refill up the coolant overflow every few weeks. However, the heater used to work just fine even when this was happening, so something else has to have gone wrong.


The heater had started getting quirky for awhile, like I would turn the blower on and have the temperature dial on red, but the heater wouldn't engage, then I'd turn the dial to blue, then quickly back to red and it would engage and start heating. Sometimes this took a few times, but then this method stopped working. The engine itself seems to heat up to operating temperature just fine, just it won't heat the air.


Now that I think about it, maybe the heating system is fine and it's the dial?

 

Arghhhh, you're killing me!!

Just start taking crap apart and fiddling with it. Take good pictures so you know where things go. That is how you will learn things. If you seriously want to keep up the Jimmy, invest in a set of GM shop manuals specific to the 98 Jimmy. There should be 3 in the set. You can usually find them on eBay.

With the additional information, yes, test the switches...

 

No worries I will look into those manuals. My problem is that I am not able per se right now to just take things apart and experiment because I need the vehicle for driving and it is also shared with my mom right now. We also live in an apartment, and they don't much favor DIY mechanics in the parking lot.

 

If both heater hoses are hot then that means coolant is flowing through the core. It's not overheating so the thermostat is not closed but it wouldn't matter anyway since coolant flows through the core even when it's closed. That leaves two things...fully open thermostat or blend door actuator. My money is on the blend door. There are quite a few threads here on the topic of changing it out going through the glove box instead of pulling the dash. The blend door directs the air flow to either the heater of the A/C duct and if it's stuck you get cold air even if your heater core is burning up.

 

Hadn't seen your post, but thank you for the information. I will look into that too. I do remember that when I would turn the heater on I think there was like a sound of a "door" snapping open or closed. Maybe that is it.

 

So I rechecked both heater hoses and I noticed that the one is hot but the other one is more warm, but not "hot" at all. Is that normal, or should both be literally HOT?

 

Both should be fairly hot but the return line will be slightly cooler due to the heat extracted. Since you're not getting heat the loss would be lessened. Best thing to do is disconnect both lines and connect a garden hose to one of the inlets to see if it's clogged. If you don't have a hardware store's worth of plumbing supplies laying around you might have to pick up a few hoses, clamps and adapters. If it is clogged alternate the flow between the two connectors. Just make sure you don't have excessive water pressure or you could blow the core. It should handle 50-60 psi without damaging it. There might be a few posts around that explain the procedure in more detail but it's not terribly difficult.