1985 M923A1 Over Heating

[Hooper]

I first noticed it in the early spring. I took the truck on a 50 mile trip in 50 degree weather. Seemed to run hot considering the weather. About 200-210. The truck was full so I figured maybe it was normal. About a month ago I took some friends for a ride around a country block. At the end of the trip the truck hit 230 ish. Yikes. My first guess was T-stat. Change it tonight. No change. The top radiator hose really doesn't seem that hot. I was thinking about pulling the stat out to see if I can determine between the Radiator or water pump. The water pump looks really basic so I'm wondering if it would really be a problem. Anyone have any other ideas?

 

[Hooper]

Just checked on it. The pipe coming out of the thermostat housing is hot. The oil cooler is hot. But the radiator is cold?

 

[SLOrazorsedge]

The gauges in these trucks are inherently in error, a infrared laser gun is your friend. Shoot the various components for an accurate temperature read.

 

[Hooper]

After the test run last night steam was coming out of the small hose end at the thermostat housing. I found a thread by another Steelsoldier poster tbar123. Had all the same symptoms as me and it turned out to be a plugged radiator. Last night I was laying in bed thinking about it and convinced myself that it must be the radiator. I will attempt to flush it in a few weeks and post the results here. Thanks for your response.

 

[Hooper]

With some of the issues I've seen with RR trucks, I'm embarrassed for the RR people. Many of these trucks would have cost American soldiers their lives if in a combat situation.

 

[patracy]

Fan clutch working?

 

[Hooper]

Fan clutch working?

Yes, it seems to kick on at the correct temp. Right around 200. That's actually what tipped me off to the problem. I was driving it around my house and it had only been running for 30 minutes when the fan began to run.

 

[74M35A2]

Rare, but could be the water pump also from what you are describing. An impeller can disintegrate or come off the shaft. Oil cooler is probably warm from trans heating it. You could pull a heater hose off, start it, and see if coolant pumps out, this would be a quick test to check water pump flow.

The radiator on my 1990 M925A2 sprung a leak at the side tank. I decided to go new radiator, and when they unbolted the side tanks, I was surprised it had any cooling at all, the tube ends were so plugged up with yuck. I think CLR would be the only thing to really attack a mineral clogged core, and that stuff is not cheap in the amount required. Some people report of using Cascade dishwasher soap, but I don't know if that dissolves minerals, it may just be general soap that cleans. If you can confirm the water pump impeller is good, then a new radiator may be the best way to go, as long as you already did the stat like you said. I have seen new stats be bad though also. I paid $550 for my radiator, brand new, custom made at a radiator shop using my original for the dimensions. Detroit Radiator Corp (DRC), I think.

 

[tbar123]

One thing I did notice when I took the radiator out was that the crossover pipe to the top rad hose was almost rusted through. To me that gave me an inkling that the rad was plugged. I would take that top hose loose and see how bad that pipe is! I bought a 2 3/8" galvanized fence post for about 12 bucks,which was long enough for the crossover and the pipe leading to the trans cooler!

 

[Hooper]

Thus far the thermostat did not change anything. After reading some older posts I was thinking the radiator my be the issue so I went for that next. I drained the coolant and thought I would try starting it to see if any coolant came out of the thermostat hose, nothing. Thinking that was odd I thought I would check the radiator. Back flushed it and it is flowing perfectly. I'm down to the water pump, the air pump leaking into the coolant system or possibly a head gasket. I'm digging into the water pump but I'm scratching my head on how the water pump belt is tensioned....Got it, pump looks fine. So it seems like either the air pump or head gasket are pressurizing the cooling system. How difficult is it to tear apart an air pump?

 

[OilfieldRoughneck]

Inspect the water pump. Mine was shot and would do similar things

 

[Hooper]

Inspect the water pump. Mine was shot and would do similar things

Impeller looks new, what was wrong with yours?

 

[OilfieldRoughneck]

My impeller was worn out, and the bearing was going out. Causing belt slippage and failure.

 

[tbar123]

What I would do ( after fighting the same battle) is to take every single hose off, flush them with a pressure washer. Then hit the trans cooler. Run a rod down all the ports in the trans cooler. Back flush the heater core then forward flush a good few times. Then Remove your inspection plates and power wash the heck out of the block. I also flushed my radiator and it "seemed" to flow correctly, but after removing it I learned that was not the case. Remove the nut on top of the passenger side radiator shine a flashlight into the lower radiator hose and see how it looks. If it's rusty color and has calcium build up then better remove the rad and power wash it clean. Did you happen to boil test the thermostat? If not since you have everything apart boil test it for proper function, Before it closes slip it into the housing to make sure it closes properly. I remember someone saying that their thermostat didn't close in the housing and had to sand the ring down a bit for proper function.After draining and filling my system time after time to see if that fixed. I would seriously suggest just doing everything I just described and to be done with it. Also you may want to put new clean filter,fluid, and distilled water in.

 

[Hooper]

What I would do ( after fighting the same battle) is to take every single hose off, flush them with a pressure washer. Then hit the trans cooler. Run a rod down all the ports in the trans cooler. Back flush the heater core then forward flush a good few times. Then Remove your inspection plates and power wash the heck out of the block. I also flushed my radiator and it "seemed" to flow correctly, but after removing it I learned that was not the case. Remove the nut on top of the passenger side radiator shine a flashlight into the lower radiator hose and see how it looks. If it's rusty color and has calcium build up then better remove the rad and power wash it clean. Did you happen to boil test the thermostat? If not since you have everything apart boil test it for proper function, Before it closes slip it into the housing to make sure it closes properly. I remember someone saying that their thermostat didn't close in the housing and had to sand the ring down a bit for proper function.After draining and filling my system time after time to see if that fixed. I would seriously suggest just doing everything I just described and to be done with it. Also you may want to put new clean filter,fluid, and distilled water in.

Thanks, I think I will do that. I read another guy had a problem with air pump bleeding air into the coolant system. I will start by cleaning the crap out of the cooling system first. Then bleeding every thing real well.

 

[Swamp Donkey]

Thanks, I think I will do that. I read another guy had a problem with air pump bleeding air into the coolant system. I will start by cleaning the crap out of the cooling system first. Then bleeding every thing real well.

If you want to rule out air in the coolant, look for it in the overflow tank with the engine running and the air built up to full pressure. You're looking for rising bubbles, not standing bubbles from vibration. The two possible areas air could get into the coolant are from the compressor and the shutterstat. I'm not saying that this is your problem, just letting you know where to look.

 

[Hooper]

If you want to rule out air in the coolant, look for it in the overflow tank with the engine running and the air built up to full pressure. You're looking for rising bubbles, not standing bubbles from vibration. The two possible areas air could get into the coolant are from the compressor and the shutterstat. I'm not saying that this is your problem, just letting you know where to look.

That's sweet thank you. I'm pretty sure I have ruled out the major component's as in the T-stat, water pump and radiator. When it over heats, the radiator never gets hot. Since the pump is fine, it must be unable to work because of the air pockets.

 

[porkysplace]

That's sweet thank you. I'm pretty sure I have ruled out the major component's as in the T-stat, water pump and radiator. When it over heats, the radiator never gets hot. Since the pump is fine, it must be unable to work because of the air pockets.

Or the radiator core is plugged.

 

[Hooper]

[/COLOR]
Or the radiator core is plugged.

Water is flowing fast from one side to the other. When it over heats the radiator never gets warm.