6CTA m939a2 overheating issue

[dawico]

My MV is a 1990 m923a2 with the 8.3l Cummins and I have owned it for four months or so.

Searching the forum hasn't revealed any help and the TMs give little support.

Here is my issue. The coolant overflow was empty 3 weeks ago. I filled it with coolant mix and drove it 45 minutes. It stayed parked for three weeks until yesterday. I have never had the engine temp gauge read above half way but just before filling the reservoir was the first time I have heard the fan run.

Yesterday showed normal operation and temperature levels on the 45 minute ride back home at about 60°. The truck fired right up which is normal.

This morning was about 32° and the truck started hard which is unusual but not suprising given the temperature outside. During my normal warm up walk around inspection the reservoir started spitting out coolant. Not really blowing it out, but it was definitely getting rid of it.

Losing coolant and lots of rust.

Driving the truck the temperature gauge steadily climbed to almost 240° before I stopped. After it cooled I tried again and had the same result. I did not shut the truck down and it only took a few minutes to cool.

This happened three times total before I got back home. I did not let it boil over and the fan was definitely working.

I checked the oil and transmission fluid and didn't find any evidence of coolant present (per the TM). All fluid levels were fine except the coolant reservoir which was empty again. The spill over didn't appear to have any oil in it.

So conventional wisdom says to replace the thermostat and flush the system to get the rust out.

Is the thermostat available anywhere besides Cummins (pn 204586)? Hoping for a local auto parts source.

Is there anything else I should be looking at? Anything else to test or try before I start tearing it apart?

Does a thermostat sound like a reasonable fix? It is cheap enough anyways but doesn't really explain why the coolant was spilling out before it even warmed up.

Any help or advise is appreciated.

 

[R Racing]

I'd say either thermostat. Or coolant leak. As in broken hose clamp or in hole in a hose. And or shutterstat. Your loosing it out of somewhere ??

 

[Jason O]

Your T-stat is opening (at least part way), as the fan shutter-stat is reaching 180 and running the fan. Is the radiator getting hot also? Hot inlet at top and cold outlet at bottom of the radiator could mean minimal coolant flow.

Is the coolant system building pressure before it reaches temp?

 

[R Racing]

The shutterstat could also be leaking air in the system and pushing out fluids ?

 

[Suprman]

The 8.3 has 2 thermostats next to each other. They are housed by the alternator. There are a few gaskets used in the replacement process along with 2 thermostats and thermostat gaskets.

 

[dawico]

I'd say either thermostat. Or coolant leak. As in broken hose clamp or in hole in a hose. And or shutterstat. Your loosing it out of somewhere ??

Just the overflow is losing coolant and it didn't appear to spit any out while driving.

 

[dawico]

Your T-stat is opening (at least part way), as the fan shutter-stat is reaching 180 and running the fan. Is the radiator getting hot also? Hot inlet at top and cold outlet at bottom of the radiator could mean minimal coolant flow.

Is the coolant system building pressure before it reaches temp?

I will check the radiator tomorrow, as well as refilling the reservoir to see if it blow out again.

I will also check the hoses and see if they build pressure while running cold.

 

[dawico]

The shutterstat could also be leaking air in the system and pushing out fluids ?

I read about that in another thread. Any way to check that or test it?

 

[Tornadogt]

Subscribed, I have one doing the same thing and just havn't had time to do anything about yet. I am also leaning to a thermostat problem, My intentions are to replace the theromatstats and a good flush of the system and give it a try... keep us updated it may save me a step or two....

Thanks..

 

[Tornadogt]

I read about that in another thread. Any way to check that or test it?

You can bypass it and have the fan on all the time for testing, OR remove the Shutterstat from the coolant tube.. Submerge it in water and see if it blows bubbles..

 

[Monkeyboyarmy]

Go around and check every hose clamp. You will probably get a couple turns on them. Even the 2 behind the rear head. The colder it gets, the more they leak.

 

[dawico]

The 8.3 has 2 thermostats next to each other. They are housed by the alternator. There are a few gaskets used in the replacement process along with 2 thermostats and thermostat gaskets.

I didn't see anything like that in the TMs. My thermostat housing didn't match the picture either. I will have to check again. Maybe what I saw was for the engine in the a1 (NC250 or whatever).

Thanks for the info.

 

[Suprman]

It's in there. You can order the gasket set from cummins its around 80 bucks not including the thermostats and their respective gaskets. It's a real problem when that engine runs hot. Very easy to kill a head gasket or worse. If your coolant looks rusty you should do a full flush. Hose the whole system out.

 

[63foxtrot]

just went through the whole ordeal last month. new engine fixed it.

 

[Coffey1]

When you filled it did you bleed it . It may have air in the system.
There's a bleed vent on top front of intake you are suppose to open while filling until fluid comes out of that bleed valve.

 

[dawico]

just went through the whole ordeal last month. new engine fixed it.

I think that will be the last thing I try.

 

[dawico]

When you filled it did you bleed it . It may have air in the system.
There's a bleed vent on top front of intake you are suppose to open while filling until fluid comes out of that bleed valve.

No, I did not bleed it. I know about the valve but didn't even think about it.

I think the shutterstat will be my main objective to test. Pumping air into the coolant system makes sense at this point. The coolant started to run as soon as I started it up this morning, immediately upon the tanks building air. The thermostat was nowhere near opening at that point.

I also plan on checking all the hose clamps and flushing the system.

I will report back with any findings or other questions that come up.

Thanks again guys.

 

[74M35A2]

Each their own, but I think you could do a little more diagnostics before you start throwing parts at it. The next thing I would look at is what is the temp of all the coolant hoses? Is the engine hot, but top hose cold? This would be stuck thermostat. Is the heater blowing cold but the engine is hot? This could be air in the system.

I just did the thermostat in my 8.3, and there was only a single thermostat. I ran my engine number through Cummins to determine what I needed, and I obtained it from them. My temp would rise slow, and then cool off on the freeway. After a new stat, it now warms a little faster, but holds a solid 180F even at 67mph and 10F outside temps, no winter front or grill cover.

Many flush their system with Cascade dish washing detergent. The stat should hold temp at 180F, and the fan turn on at 200F. That is what mine does anyway. The fan and stat should not have the same temperature set points. Fan should always be higher.

You could also leave all your tank drains fully open, so the system can't build air, start it, and see if the boil overs stop.

 

[dawico]

Each their own, but I think you could do a little more diagnostics before you start throwing parts at it. The next thing I would look at is what is the temp of all the coolant hoses? Is the engine hot, but top hose cold? This would be stuck thermostat. Is the heater blowing cold but the engine is hot? This could be air in the system.

I just did the thermostat in my 8.3, and there was only a single thermostat. I ran my engine number through Cummins to determine what I needed, and I obtained it from them. My temp would rise slow, and then cool off on the freeway. After a new stat, it now warms a little faster, but holds a solid 180F even at 67mph and 10F outside temps, no winter front or grill cover.

Many flush their system with Cascade dish washing detergent. The stat should hold temp at 180F, and the fan turn on at 200F. That is what mine does anyway. The fan and stat should not have the same temperature set points. Fan should always be higher.

You could also leave all your tank drains fully open, so the system can't build air, start it, and see if the boil overs stop.

Running it with the tank drains open was exactly what I had in mind to test the shutterstat or any other air pressure in the system issues. I still need to narrow it down from air pressure or a head gasket/ combustion chamber pressure issue.

If the air pressure issue does stop by opening the tank drains then I will isolate the shutterstat and test it. I will go from there.

I have no intention of throwing parts at it at this point until I find a culprit. I was just going to get a thermostat but that is even out now too because of the complications of this system (air compressor involvement).

 

[doghead]

Try following the instructions in the tm?