M1009 Wont Warm Up

79Vette

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Well, I am not sure what to try from here. I just replaced my thermostat for the second time with another Delco 132-55 (GM 14077122), and the truck still will not warm up above 160F. I have a Vintage Air system with a block off valve in the heater circuit, so there is no flow through the heater core unless you activate the heater, which I have not been doing. Its been in the 60s in SoCal, so I would expect the truck should have no problems warming up without a radiator block off.

The truck starts and runs fine, but I am getting ~14 mpg and I think getting the engine up to proper operating temp might make that 1-2 mpg better. Also, it seems like oiling system performance and consequently engine life would be improved at the correct temperature. The truck has got awful mileage for years, but I just recently installed temperature gauges and was previously unaware of the cold running issue.

My water temp gauge reads just over 160F after a long drive (sender in factory location), and the IR thermometer reads 165F at the thermostat housing. Oil temp gauge barely registers at 140F (sender at the plugged boss above the oil cooler lines), and the fittings in the oil cooler lines measure 145F on the hot side and 80F on the cold side. I think I can rule out defective gauges at this point, based on all the readings showing the engine is running cold.

Is there any way the coolant can bypass the thermostat? Am I just getting defective thermostats? I can't comprehend how the engine could run at 160F forever with no coolant circulation...
 

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royalflush55

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Fan clutch may be locked up and pulling too much air all the time.
Thermostat should open when water temp reaches 180* inside engine. After that radiator and air flow take over. Check that with your IR gun. You can put thermostats in a pan of water on the stove and they will open at the designated temperature on a thermometer. A lot of mechanics will verify they work this way before installing.

Put a cardboard in front of radiator and see if it warms up any better going down the road.
 

LT67

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Similar issue with the 6.2 in my 86 M1008. It never gets above 145 degrees with a new 180 thermostat. Turns out the engine is losing compression...
 

cucvrus

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My opinion may matter very little but I think I would check out the heads and head gaskets. I had an M1009 that I ran for 4 years with good heat in city but when I was on the highway the heat was gone. I always had a hard pressurized top radiator hose and never had any oil in the water or water in the oil. I ran it that way for a few years and one day in Winter I started it up and drove to town. It was a steam pipe out the right side. The time had come. I removed the engine and pulled the heads. Sure enough it was the compression seal on the head gasket. Now was the time to correct it. The 1 cylinder that was effected was spotless clean and the others were black with diesel smoke normal. So that is my guess. It is fairly easy. Just make sure to do it right. I would pull the engine and go over every seal and gasket. Good Luck.
https://www.steelsoldiers.com/threa...engine-survey.137671/#lg=post-1713523&slide=0

Check out this thread. At the time I had 2 brand new 6.2 diesel engines in the crates and still choose to rebuild my engine. I have since sold this truck as you will read in the postings. Good Luck. And don't take short cuts and do it right the first time. new head bolts do the job you don't need studs and other fancy stuff. It is a 140 HP engine not a race truck. Happy Holidays.
 

79Vette

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Thanks for all the input so far.

With the engine off and cold, I can spin the fan easily by hand. I assume this means the clutch is not locked up?

The engine starts and runs well for what it is, so I don't think I want to just pull it out blindly. I'll purchase a diesel compression tester next week and check each cylinder, and post back with what I find. If there is a problem, then I will think about removing the engine for repairs.

In the meantime I'll add some cardboard to the radiator and see if that makes a difference, and I'll check the thermostat I took out in water on the stove and see where it opens.

However, I don't understand how the engine can run colder than the thermostat. If the coolant is not circulating, how is the heat being removed from the engine? This isn't an air cooled motor, so it seems like a closed thermostat would cause the engine to warm up until the thermostat opens regardless of fan speed, radiator size, outside temperature or anything else . Am I missing something?
 

Mullaney

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Thanks for all the input so far.

With the engine off and cold, I can spin the fan easily by hand. I assume this means the clutch is not locked up?

The engine starts and runs well for what it is, so I don't think I want to just pull it out blindly. I'll purchase a diesel compression tester next week and check each cylinder, and post back with what I find. If there is a problem, then I will think about removing the engine for repairs.

In the meantime I'll add some cardboard to the radiator and see if that makes a difference, and I'll check the thermostat I took out in water on the stove and see where it opens.

However, I don't understand how the engine can run colder than the thermostat. If the coolant is not circulating, how is the heat being removed from the engine? This isn't an air cooled motor, so it seems like a closed thermostat would cause the engine to warm up until the thermostat opens regardless of fan speed, radiator size, outside temperature or anything else . Am I missing something?
.
I didn't have the military version, but the truck that I had always ran cold. If you wanted heat in the winter, blocking off about half of the radiator was a requirement.
 

Skinny

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Thermostat doesn't open at 180 degrees, it's meant to operate at 180 which requires it to open sooner.

Having said that, mine will run dead nuts on 160 all day long cold or hot out. If I'm getting on it hard and cruising her at 80mph (thank you 4L80) it will climb to like 190ish depending on throttle usage.

Sure something may be wrong but you may be chasing your tail. If it was hovering in the 150 or below range I'd be more concerned.
 

LT67

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My 86 m1008 has low compression and it takes longer to warm up to 145 degrees... and that's as high as it'll go. There's still enough heat in the cab to keep me warm in the winter.

I don't have a separate temp gauge on the 85 m1008, but that thing will roast me out of the cab in the winter😛
 

Squibbly

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My opinion may matter very little but I think I would check out the heads and head gaskets. I had an M1009 that I ran for 4 years with good heat in city but when I was on the highway the heat was gone. I always had a hard pressurized top radiator hose and never had any oil in the water or water in the oil. I ran it that way for a few years and one day in Winter I started it up and drove to town. It was a steam pipe out the right side. The time had come. I removed the engine and pulled the heads. Sure enough it was the compression seal on the head gasket. Now was the time to correct it. The 1 cylinder that was effected was spotless clean and the others were black with diesel smoke normal. So that is my guess. It is fairly easy. Just make sure to do it right. I would pull the engine and go over every seal and gasket. Good Luck.
https://www.steelsoldiers.com/threa...engine-survey.137671/#lg=post-1713523&slide=0

Check out this thread. At the time I had 2 brand new 6.2 diesel engines in the crates and still choose to rebuild my engine. I have since sold this truck as you will read in the postings. Good Luck. And don't take short cuts and do it right the first time. new head bolts do the job you don't need studs and other fancy stuff. It is a 140 HP engine not a race truck. Happy Holidays.
I like what you did in that thread.
For me anyways, repairing the old engine rather than dropping in the new crate if at all possible (and you have the skill to do it) would be the choice too.

Some of the joy of having these old things and repairing them is the 'soul'.
The shit that engine may have seen. All the people it may have carried. The reliability it provided even when it was "injured", and bleeding fluids.

You almost have to fix that shit out of respect. 😀

I thought a leaky head gasket would actually cause an overheat issue, not an under heating issue. I trust your input though. I've read your other posts and you clearly know how to fix this stuff.

My pops has a "Prius" (stop laughing), that had a similar issue and it was because Prius' suck, and you have to bleed all the air out of the coolant system or it'll get a "bubble" and not get to temp (and throw a CEL). Not sure if these vehicles can suffer from the same fate (I only recently got one), but it is possible there is air in the system?

I read on another thread just now that another person had the same low reading on the gauge, and they removed the sending unit, and put coolant in from that opening, and sure enough it was an air pocket that wasn't letting the sending unit read the correct temp. Just a thought.
What is the correct operating temp? | SteelSoldiers
 
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