1991 BMY M923A2 loses heat when temp gauge hits 200 degrees

[Western PA M923A2]

Well I guess a digital IR thermometer will be the next tool I buy! As to my temp gauge, it's brand new, just put it in like 4 or 5 weeks ago.

 

[WillWagner]

Well I guess a digital IR thermometer will be the next tool I buy! As to my temp gauge, it's brand new, just put it in like 4 or 5 weeks ago.

That means nada, they are known to be "erroneous". Verify it with a known good one.

 

[Western PA M923A2]

I hear ya. I'm a technician by trade and I've had bad parts that were brand new. One other thought... could there be air trapped in the system causing these issues> If so, what's the process to bleed out the air?

 

[98G]

If it were a 6.7 or a 5.9 cummins in a pickup truck, your symptoms are spot on for head gasket failure. The very close similarity of the 8.3 make it really suspicious that that is the case here as well....

 

[Csm Davis]

The sender is bad most of the time when the gage is reading to high from my experience. Clean out your cooling system 99% are full of muddy gunk and the tank looks pretty and green.

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[WillWagner]

Air in the system is purged out by the vent line at the front of the cylinder head and deairiation line from the top of the tanks to the surge tank.

The only similarities between the B series and C series are 6 in line cylinders. Two totally different engines.

 

[Jason O]

Whats you trans temp running? Temps should run fairly close together, once everything is warmed up due to the heat exchanger in the coolant loop.

Where in western pa are you? I'm in Washington, and keep a truck or 2 at my shop in Carnegie.

Jason 717-673-0845

 

[Western PA M923A2]

Hey Jason, thanks for the reply, and Merry Christmas! I'm in West Newton, not far from Washington, like 30 miles.

 

[Western PA M923A2]

Well. tomorrow I'll start off with draining the coolant, and hope that globs of crud come out of there and then try and flush the rad out and see what happens. I have a gut feeling there's blockage somewhere/ Let the truck run for like 30-45 min. today, and after the temp gauge hit around 150, I had heat, and with an IR thermometer, I hit the heater hose in the cab and had around 120 degrees, and the cab was warm & comfy... but a few minutes after the t-stats opened, heat goes away, then the temp rises above 200, so I shut her down. I'm guessing (and hoping!) that once the stats open and the coolant starts to flow (or maybe TRIES to flow) through the system, it's hitting blockage, so we shall see. BTW, checked the oil... totally full and NO coolant in there, and no oil in the coolant, at least none that I could see, so hopefully it will be that way when I drain it.

 

[Western PA M923A2]

Okay, coolant drained from rad. Nice brownish/greenish color but not nearly as bad as I expected. No evidence of oil in there either, Next, pulled the hose above the t-stat housing... nice, nasty, diarrhea brown crud! Getting ready to pull the housing after my coffee break.

 

[goldneagle]

You may want to consider installing a bypass coolant filter. I did it in all my trucks. You can see the install in my 5 ton thread.

 

[Western PA M923A2]

Okay, latest update - pulled the t-stat (p/n 391302 and it looks pretty cruddy, and the internal bypass t-stat below there, well there wasn't even one in there! Could that be a factor with the loss of heat/temp rising?

 

[Ford Mechanic]

Okay, latest update - pulled the t-stat (p/n 391302 and it looks pretty cruddy, and the internal bypass t-stat below there, well there wasn't even one in there! Could that be a factor with the loss of heat/temp rising?

View attachment 659696 View attachment 659697

There's not supposed to be 2 t-stats in the truck. At least Cummins doesn't list it. I've just had mine apart, make sure you replace all the gaskets in that area after you disturb any of it.

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[Western PA M923A2]

Look in the TM 9-2320-272-24-1, pages 3-192 thru-3-195

 

[simp5782]

Look in the TM 9-2320-272-24-1, pages 3-192 thru-3-195

Like I said a few pages ago. Some trucks are not equipped with them. Some only have 1 thermostat, some have 2. Take your pick and your best guess when going off into these. It is hit or miss on what is what. Some 6 CTA engines will have 1, 2 or even the bypass thermostat. There is no right answer.

 

[Western PA M923A2]

Well I already got the internal t-stat at Napa and it was only $14, and they're going to have the main external bypass stat in tomorrow, so I'll put them both in and hope for the best.

 

[wrenchturner6238]

In a post a few pages back talked about flushing the system with cascade and water. I can agree with that and what others have said. I just want to caution you that if you only use straight water during this process and its below freezing it will freeze in your radiator. I am just giving you a reminder about the time of year your are doing this.

 

[Western PA M923A2]

Point taken... and the weather here this week is supposed to be in the 40s-50s, so I think I'll be in good shape.

 

[WillWagner]

Give me your esn and i'll check if it a two stat build. IIRC, some vehicles with an auto trans had just one stat so there is a positive flow through the lower rad hose and trans cooler with the stat closed.

That stat looks wrong and it should have have been in the hole on the left of the pic, the little hole in the bottom of the hsg is the block loop cooling port. When the stat opens, there is a dis on the bottom of the stat that is supposed to cover the block loop route and direct coolant through the radiator. Let me see if I can find a pic

 

[WillWagner]

They look like this....