Heater Problem!

I have a 97 Jimmy with 98k on it. Starting this winter my heat is not warming up as it used to. The air coming out is a bit warm but not hot and doesn't warm up the whole car. Living in Minnesota and on a day like this when it's -11 F my ass is freezing up in the truck. I don't know if it's the thermostat which i never changed since i got the truck. I heard they last about 60k, or something is wrong with heater core or does it have to do with the coolant? I don't know much. Does anybody have an idea of what's wrong and what can be done? Thanks!

I would start with the thermostat. Has it ever been replaced? sounds like its sticking open slightly.

If you replace the T-stat, its always a good idea to run a cooling system flush while you are at it, flush the cooling system and then flush the heater core seperately.

If your heater core is clogged, wait until your truck is warm and feel the hoses right at the firewall as they go into the heater core. Both hoses should be warm or hot. If one is hot, and the other is cold, then BAM your heater core is clogged. Like I said before, flush the heater core by taking off both the hoses at the firewall and turn your garden hose on and *gently" run water through one of the ports. Junk should splash out the other end, if its in fact a clogged/dirty heater core. You dont want to run "blasts" of high pressure water through a heater core, if its weak then you just created a big problem. When I have flushed heater cores in the past, I always use spurts of medium pressure garden hose water. Always been good enough for me :)

Hope this helps!!

Ok i'll replace the thermostat because it has never been replaced and i'll have them do the flush too. How much is a thermostat anyway? But i also have another problem which is that i'm only getting around 210 miles or lower on a full tank for the past couple of months. I'm not exagerating. I don't know if it's related to the heater problem but l used to get around 270 miles in the winter. A full tank last about 4 days. Can anybody give me an advise on that because my truck has become a true addict to gas :)

First thing check to make sure your coolant is correct level. Fill if necessary with DexCool 50/50 mix (you can go up to ~65% Dexcool/35% distilled water). Above that and the fluid doesn't transfer heat as efficiently. You know to NEVER add plain water to your coolant right?

Also check the consistency of the Dexcool in the reservoir. Is it fluid or is there some gelatinous goo forming? Goo is bad. Replace coolant if you are not sure. Dexcool is "supposed" to last up to 150k miles. But it still needs to be checked. Also test the coolant with a gauge you can get at your auto parts store. This just tests to see if the additive package in the coolant are still at sufficient levels. Of course you know to never mix the ethylene glycol coolant (fluorescent green) with propylene glycol Dexcool (reddish-orange).

Next get your truck up to temp and then check the coolant hoses.

The upper radiator hose (3" outter diameter black) comes out of the driver side of the raddy and goes into the thermostat housing. The lower raddy hose (3" outter diameter black) comes out of the lower passenger side of the raddy and attaches to the water pump.

With your engine up to operating temperature, is the upper raddy hose nice and toasty warm? It should be if the thermostat is opening correctly. I think stock thermostats on your model are 195 F (correct me if I'm wrong guys). So your engine needs to get above 195 to pop the thermostat and start cycling coolant through the raddy. If your engine is up to temperature and the upper raddy hose is still cool, then that indicates you may have a thermostat problem. They supposedly only last about 60k miles or so before they start losing perfomance (ie. partial opening, or sticking in closed or open position).

The thermostat is easy to replace. Less than a half hour even if you take your sweet time like me (ie. clean off all the seepage and junk around the engine and give everything a good once over). I'm not sure if you need waterpump RTV sealant on the gasket or not for your model. Check your manual. You will want to put teflon based white thread sealant on the bolts. Any bolt that goes through the water jacket of your engine should be sealed to prevent leaks and corrosion of your bolts.

Now if your upper raddy hose is toasty, and your lower raddy hose is toasty warm, that means that you are getting proper coolant flow through your radiator and engine. Your thermostat is not the problem (but since yours is old, preventive maintenance says change it anyway :).

Now locate your heater hoses. These are about 1" outer diameter black hoses. One should attach from the passenger side of the radiator and run to the back wall of the engine compartment where it attaches to the heater core. There is another hose that comes from the heater core and goes to the engine (attaches to the lower intake manifold or the water pump depending on your model).

IF both upper and lower raddy hoses are warm, AND your heater hoses are cool, THEN you have a problem with your heater core. It might be plugged [radiator Stop Leak powder is notorious for gumming up heater cores]. Something is prevent warm coolant from flowing through your heater core.

Search through the posts for more info on servicing/replacing your heater core. I hope this helps.

For your gas milage decrease, search the forum for info on fuel injector replacement. That should be a scheduled service around 100k for as often as the problem comes up.

Ok i'll replace the thermostat because it has never been replaced and i'll have them do the flush too. How much is a thermostat anyway? But i also have another problem which is that i'm only getting around 210 miles or lower on a full tank for the past couple of months. I'm not exagerating. I don't know if it's related to the heater problem but l used to get around 270 miles in the winter. A full tank last about 4 days. Can anybody give me an advise on that because my truck has become a true addict to gas :)

How high does the temperature get on the gauge?

1/4, 1/2?

Ok i'll replace the thermostat because it has never been replaced and i'll have them do the flush too. How much is a thermostat anyway? But i also have another problem which is that i'm only getting around 210 miles or lower on a full tank for the past couple of months. I'm not exagerating. I don't know if it's related to the heater problem but l used to get around 270 miles in the winter. A full tank last about 4 days. Can anybody give me an advise on that because my truck has become a true addict to gas :)
The problems could be related... if your thermostat is stuck open. A stuck thermostat would not allow the engine to reach normal operating temperature, this would cause your heater to blow warm or cool instead of hot. Also if the engine doesn't reach the proper operating temperature the computer won't go into closed loop, this will cause a decrease in fuel economy.

What does your temperature gauge show?

I have a 97 Jimmy with 98k on it. Starting this winter my heat is not warming up as it used to. The air coming out is a bit warm but not hot and doesn't warm up the whole car. Living in Minnesota and on a day like this when it's -11 F my ass is freezing up in the truck. I don't know if it's the thermostat which i never changed since i got the truck. I heard they last about 60k, or something is wrong with heater core or does it have to do with the coolant? I don't know much. Does anybody have an idea of what's wrong and what can be done? Thanks!

What is the temp gauge getting to?

1/4 1/2? when completely warmed up?

The problems could be related... if your thermostat is stuck open. A stuck thermostat would not allow the engine to reach normal operating temperature, this would cause your heater to blow warm or cool instead of hot.

A stuck open thermostat will DELAY engine reaching normal operating termperature. You can actually drive the vehicle without a thermostat (not recommended except in an emergency).

The engine will still get to operating temperature eventually as it heats up the entire coolant system.

In cold climates this will be more noticable.

A stuck open thermostat will DELAY engine reaching normal operating termperature. You can actually drive the vehicle without a thermostat (not recommended except in an emergency).

The engine will still get to operating temperature eventually as it heats up the entire coolant system.

In cold climates this will be more noticable.

A stuck open thermostat will delay the engine warming up, but it will not reach normal operating temperature. Read the other 2000 posts in this forum and the Blazer forum about people with stuck open thermostats, most of their temperature gauges never moved and the ones that did move never reached normal operating temperature.

You can definitely drive a vehicle without a thermostat, it doesn't have to be an emergency. If you do you will lose some fuel economy, because it burns a little richer when not in closed loop, but it won't damage your engine.

A stuck open thermostat will delay the engine warming up, but it will not reach normal operating temperature. Read the other 2000 posts in this forum and the Blazer forum about people with stuck open thermostats, most of their temperature gauges never moved and the ones that did move never reached normal operating temperature.


This just doesn't make sense. If you drive your truck long enough you should get the engine to "normal" temps. For short trips and in cold climates, then I can see a stuck open thermostat (or no thermostat) having this affect. But if you were to drive say 30 freeway miles even without a thermostat and in cold weather, then I would be surprised if the operating temperature did not reach normal levels (~210 F). Are the sensors/gauges operating properly ? And check the coolant using a coolant tester.

When my coolant system was all clogged up, my temperature gauges never budged either.

Something else would be wrong with the vehicle if normal temps were not obtainable (like the thermostat temp sensor).

I'm no expert, but the coolant system is simple and observed problems should make sense. The heat generated by the engine MUST be going somewhere.

With a stuck open thermostat, you will NEVER reach operating temperature.

I had mine stuck open and I drove for 6 hours and it never got above the 1/4 mark.

This just doesn't make sense. If you drive your truck long enough you should get the engine to "normal" temps. For short trips and in cold climates, then I can see a stuck open thermostat (or no thermostat) having this affect. But if you were to drive say 30 freeway miles even without a thermostat and in cold weather, then I would be surprised if the operating temperature did not reach normal levels (~210 F). Are the sensors/gauges operating properly ? And check the coolant using a coolant tester.

When my coolant system was all clogged up, my temperature gauges never budged either.

Something else would be wrong with the vehicle if normal temps were not obtainable (like the thermostat temp sensor).

I'm no expert, but the coolant system is simple and observed problems should make sense. The heat generated by the engine MUST be going somewhere.

We just went through this the other day in the Blazer forum. A guy said that he drove for an hour and his gauge never moved, I suggested the sending unit, gauge, or the wiring between them, BlazerLT suggested the thermostat....the guy changed the thermostat and everything was fine.

I used to have a 70's model wagoneer, when the thermostat went out I just took it out and ran with out one. It would reach operating temperature, but it would take about 30 minutes, as would most cars, but appearently the cooling systems in the newer blazers, jimmys and bravadas are efficient enough to keep it from reaching Operating Temp.

I just want to clarify... we got a little sidetracked and are not saying that this is definitely the thread starters problem.

Interesting. I'm going to have to take out my thermostat and try it. Seeing is believing you know.

Interesting. I'm going to have to take out my thermostat and try it. Seeing is believing you know.

Don't start doing stuff like this, although you complain and tell us all the problems you have been fixing on your truck, you then want to start causing problems?

Leave the truck alone, you already know what it will cause.