M939a2 overheating/excessive coolant pressure

[Jason O]

If you're thinking compressor, how about running the engine with the compressor unloaded, or its discharge piping disconnected so it never has a chance to build any amount of pressure.

 

[Suprman]

I don't think the compressor makes that much pressure run the air system properly and pressurize the coolant system that much.

 

[Ryanpowell167]

I did and it still built pressure in coolant. I also unhooked the coolant lines off the compressor and ran it and no air came out of those ports on the compressor head.

 

[Suprman]

Not much else other than combustion pressure one way or another that's going to cause your symptoms.

 

[Artisan]

FWIW

In my M925A1 I added drain down valves to both sides of my radiator and flushed out krap.

I pulled hoses off heater box and made adaptor fittings and back flushed and forward flushed several times and a ton of krap came out.

I pulled every single radiator and cooler hose and flushed back and forth and krap came out.

I pulled the plates on the engine block where you would add a block heater and flushed and krap out
that was still there after I thought I flushed it good enough, NOPE! It lays in the bottom there.

The vent lines got flushed / replaced and rerouted

I had a high volume 80PSI 3/4" garden hose w/ adaptors I made up to flush things. It so needed it.

Is it possible there is a bubble of air in the block? I know my NTC400 has a procedure for refill
so all air is purged, check your TM, you may have the same.

I would love to see a pictorial if you pull major engine components.

 

[Ryanpowell167]

Everytime I have filled it I either use the air valves in the after cooler and heater core to get air pockets out or I use my rad kit to vacuum all the air out of the cooling system and fill it. That way it isn't possible to have any air pockets. It's got to be getting pressure from somewhere because I can start it and immediately get out and climb up to the degas bottle hold my finger over the over flow and my hand on the degas bottle and it will start building pressure. So **** frustrating. Boss man has this radiator sealant **** that he had used before and if that doesn't work then I don't know what.

 

[bchauvette]

If you're thinking compressor, how about running the engine with the compressor unloaded, or its discharge piping disconnected so it never has a chance to build any amount of pressure.

You can run it with the trailer glad hand ball valve open.

 

[WillWagner]

You can unload the compressor by removing the discharge line and put shop air to the unloader, just an FYI, early diesel rngines will not turn combustion gas leak fluid green or yellow, i think it has to do with the timing differences in mechanical v.s. electronic engines. To the op, if unloading the compressor doesn,t work, you could very well have a cracked block between thr liners. Early C series engines were known for that. Also, if you overheated it prior to the head removal, you could have a cracked head between the valves on 1 or more cylinders. This was another issue they had. To try and isolate the failed cylinder, bring the exhaust valve lash to 0, then give it apx 1/4 turn tighter...yes, the valve will be open, you are doing this to relieve the compression in a cylinder. Start it and see if the pressure stops. However, if there is more than 1 cyl failed, you won't find it that way, you'll need to pull the head anyway.