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Junior Member
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12 Posts
Discussion Starter #1
I just replaced my dead PMD with the new “improved” model with a number 9 resister. The old PMD also had a number 9 resister and had been relocated to behind the front grill on a radiator support. I don’t understand why it still died, as it was new when relocated one year ago. Anyway, the problem is that the engine is now running at a much colder level than it had been. Yesterday on a 45 minute run at highway speeds, the thermostat was registering 165 degrees. I know it was not an instrument error because the heater was blowing luke warm air instead of hot air. Even while driving in the city, the temp stayed at 165 degrees. Outside temp was around 30 degrees, but this had not affected the engine temp prior to the PMD dying. The truck did sit for about two weeks before I switched out the PMD’s. Any ideas as to what would cause this, and is it OK to drive like this until it gets fixed?

Thank you,

Chip
 

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Junior Member
Joined
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3 Posts
I just replaced my dead PMD with the new “improved” model with a number 9 resister. The old PMD also had a number 9 resister and had been relocated to behind the front grill on a radiator support. I don’t understand why it still died, as it was new when relocated one year ago. Anyway, the problem is that the engine is now running at a much colder level than it had been. Yesterday on a 45 minute run at highway speeds, the thermostat was registering 165 degrees. I know it was not an instrument error because the heater was blowing luke warm air instead of hot air. Even while driving in the city, the temp stayed at 165 degrees. Outside temp was around 30 degrees, but this had not affected the engine temp prior to the PMD dying. The truck did sit for about two weeks before I switched out the PMD’s. Any ideas as to what would cause this, and is it OK to drive like this until it gets fixed?

Thank you,

Chip

Its likely your thermostat (2 if yours is a 1996 or newer) is stuck open.
 

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Junior Member
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12 Posts
Discussion Starter #3
OK, I had a feeling that might be the reason.

This is on a 1998 GMC K3500 Dually Pick-Up. Does anyone know if the two thermostats are easily accessed? Can I get directly to the thermostats or do I have to remove other parts to get to them? Are there any issues like hard to get to bolts, special tools necessary, etc.? I am not an auto mechanic, but I can do minor repairs. I am limited however with a really bad lower back. I need to determine if this is something I can do to save money, or if I have to farm it out due to my limitations.

Thanks again for the help,

Chip
 

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Man. Trans 2wd Enthusiast
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185 Posts
if your back is shot, take it in, no need to save the shop tab, just to spend it at the chiropractor. a lot of shops are lost when it comes to 6.5L, but I dont think they could even screw this one up. make sure and get genuine GM thermostats for the exact application, as some aftermarket t-stats do not play well with the 6.5L from what I hear.

as far as your failing pmd, was it mounted to a heatsink (finned aluminum plate) or just zip-tied to the grill? relocating wont do a damn bit of good unless it is on a heatsink.

I am dealing on one that failed in short order, guy relocated to the bumper with no heatsink, and it failed on him. occasionally, I have heard, a failing pmd that is failing due to heat will send the engine to a trip on the upper end of the tachometer. this truck apparently did that, as now it has a heavy miss and plenty of smoke. I think it floated the valves at redline and took a chunk out.
 
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