Engine running hot, but heater not working?

**Update Page 3** 6/24/2010

M1009 - 65,XXX miles.

The last couple times I've driven it on extended excursions (30 + miles), the coolant has tried to get hot. If I keep it around 55-60mph, the temp hangs out at ~195f. Above that and it starts rapidly climbing. I never continued testing to see how hot it would get. Even in 110f weather the temperature would be in the 'good' zone as long as I kept it under 65, and since I rarely exceed 65mph, cruising at 60 was no big deal. I did check coolant levels, which were good. Belts good, fan turning correctly, and I haven't really had time to dig into it. Now I find what must be a related issue. This morning I was headed out to chase some bobbleheads (quail ). It was the first 'cool' morning of this year. I turned on the heater, blower was strong, but the air never got more than lukewarm. There must be some correlation here.

Suggestions? Thermostat? Water pump? Plugged heater core? Where would you start digging?

I do need to get the heater working as we're headed up north in December for Christmas Tree cutting, and I don't think the wife will be happy with no heater.

Could be thermostat broken. That will cause no heat but also an overheat as the coolant travels to quickly to absorb heat. Also when the truck is ice cold start it up and see if the upper rad hose gets hard immediatly.

Well, 195 sounds like the temperature is right where it should be if it has a 195 degree thermostat. If you are not getting any heat and the engine is hot I would verify that the heater hoses going to the cab are both hot, then I would check that hot/cold damper is actually moving like it should. If the hoses are not hot your heater core is plugged.

Low coolant will also cause a hot engine but cold heater.

Ken_86gt said:

Well, 195 sounds like the temperature is right where it should be if it has a 195 degree thermostat. If you are not getting any heat and the engine is hot I would verify that the heater hoses going to the cab are both hot, then I would check that hot/cold damper is actually moving like it should. If the hoses are not hot your heater core is plugged.

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I'll check the heater hoses. But, saying 195 is right, is not correct. It's only 195 IF I keep the speed lower than normal.

This is new, BTW. I used to be able to cruise at 65-70 with no temp issues.

acesneights1 said:

Could be thermostat broken. That will cause no heat but also an overheat as the coolant travels to quickly to absorb heat. Also when the truck is ice cold start it up and see if the upper rad hose gets hard immediatly.

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That would tell me if the thermostat is stuck closed, right?

Blood_of_Tyrants said:

Low coolant will also cause a hot engine but cold heater.

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Coolant level is good.

Thermostat might not be opening all the way, just partial. If it was not opening you would not get 2-3 miles before the engine would overheat at any speed.

You might also want to check or just replace the heater hoses, one may have collapsed.

4x4 Forever said:

you might also want to check or just replace the heater hoses, one may have collapsed.

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Would that cause overheating?

check the heater hose temp when it is up to opp temp if one is hot and the other is cold you have a plugged heater core -very common or possible bad heater bypass valve

Looks like I've got a couple places to start. I'll check the above and let you guys know what I find.

ragedracer said:

Would that cause overheating?

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Nope, but it would let you know about not getting any heat to the heater core.

Ok. So here's where we sit. I'm thinking it might be the thermostat going bad. I popped the hood and checked all the usual. Fluid a nice green and full. Very clean looking. All hoses in good condition. No leaks evident. To get a feel for what empty vs. pressurized hoses felt like, I gave them all a squeeze. The upper rad hose in particular. I then took it for a spin. It's currently 75f here. I had it warmed up to 200f in ~5 minutes, never exceeding 25mph. I was watching the temp gauge very carefully. All of a sudden the temp dropped almost 15 degrees. Hmm. Haven't seen that before. Turned on the heater. HOT air. I didn't get it out on the freeway, as I'm low on diesel and the nearest diesel station is 5 miles in the opposite direction of the freeway. But, I'm thinking it must be the t-stat. Either it was stuck closed or open, and the action of me pumping the upper hose maybe unstuck it?

Some time this week I'll see about putting a new T-stat in it, unless any of you have any other ideas? 195f is the correct t-stat, right?

Edit to add: All hoses were hot to the touch. Both heater hoses and upper and lower hoses at the end of the drive.

If you are going to tear that far into it go ahead and change the radiator and heater hoses...if finances permit. Maybe even the water pump, I would. Cheap peace of mind.

It does sound like you unstuck something.

Thermo at 195 sounds good.

4x4 Forever said:

If you are going to tear that far into it go ahead and change the radiator and heater hoses...if finances permit. Maybe even the water pump, I would. Cheap peace of mind.

It does sound like you unstuck something.

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I actually changed all the hoses in October of last year when I first got it. I don't think they are an issue. Water pump? I don't know. I might. But I want to go after one piece at a time. If I replace a bunch of stuff at once, and it's still doing it, I won't know what new part isn't working right.

ragedracer said:

I actually changed all the hoses in October of last year when I first got it. I don't think they are an issue. Water pump? I don't know. I might. But I want to go after one piece at a time. If I replace a bunch of stuff at once, and it's still doing it, I won't know what new part isn't working right.

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Oh, didnt know you had changed the hoses, they should ok for 3 years or so.

Just go with the new thermostat then, 195 sounds good.

Allright! Well it looks to have been the thermostat. I replaced it with a 180* thermo (it looks like a gasser thermostat, but they swear it works the same? If not, and I must get the 'hockey puck' looking thing, please let me know). So far, it's been running dead on the nose 180. I did end up replacing a heater hose (lower) due to my previous routing. I noticed a pretty severe rub on it. However - OOPS! I think I cracked the hose 'bib' to the heater core. It leaked a little bit into the cab for the first 30 minutes of running, but has now quit. I don't know what the story is there, something to keep an eye on, I guess.

I also replaced the glow plugs. Again. I bought some from ssdiesel supply last year, and within a week they had gone bad. Since weather was warming up, I didn't bother replacing them. Now that it's cooling off, it was getting a little hard to start. A set of AC 60g's, and it fired RIGHT up. I almost forgot how easy these engines are supposed to start. We'll see how long these last. Checker says they have a 3 year warranty, so hopefully they last longer than that!

Good, it sounds like you found your problem! On another note I want to mention that my 1008 has had a problem with that a little aswell....Mine was a huge air bubble in the upper radiator hose caused by previous owner doing a coolant flush and not "birping it"....I dont know if it's an issue with upper hose on all 6.2's but it's just about even with the cap, which absolutely has to be the highest point in the system. I pulled the truck up on a hill and had a buddy hold the upper hose as low as he could while i filled the excess....over a half gallon. Hope this helps someone, it threw me for a loop for a minute or two!

Overheating at speed is an indication of a bad fan clutch.

The reason speed inhibits cooling is the turbulence that develops in front of the vehicle which actually reduces airflow when you exceed a certain speed. You already have the understanding based on your narrative that beyond a certain speed, your truck would run "HOT".

You can check your fan clutch by checking it when the truck is not running. Give the fan blade a spin and observe how far it turns past where you let it go. A good clutch should stop the fan in just a 1/4 turn or so. Also, if there is any squeaking or rubbing noises coming from the clutch when you turn the fan with the engine off it is time to replace it. Spend the extra money and get the "HEAVY DUTY" fan clutch rated for over 8500 GVW.

I checked the TM for the CUCV and it indicates that the 6.2 is equipped with a fan clutch but I could be mistaken and if your truck does not have one, then I am off base.

Just my two cents

RL

Ive been trying to get heat out of my 1009 for about a week. Id replaced the radiator w/ a new old stock, still in the box Harrison a few months ago and added a coolant filter in line with the heater core intake. Thought this year would be warm commutes. Much to my dismay I have not had the "hair dryer" heater I was thinking I would have. Heater core is almost a year old, coolant filter was added just before the radiator went in.

I ended up replacing the thermostat this past week and found that the $11 AZ special rated for 195F has a working life of about 3 years. And the heat, while warmer than before, just aint that warm. Certainly not like my new M1008, my god. Im guessing the thermostat in that thing is isnt a 195, probably a 200+ something or other. No cardboard up front either unlike the blazer. Heater lines are hot on the blazer. I just dont understand.

Whats up with the blazer?? Someone suggested a vaccuum line but I believe the blazers heater controls are cable actuated.