NTC 400 Cummins Coolant in the engine oil

[Southern Krawler]

Hello everyone I started working on my M920 today after almost 2 years of procrastinating . The previous owner disclosed it had engine trouble and I bought it priced accordingly. After much difficulty finding affordable transportation I finally got it home and layed my eyes on it for the first time. I was really amazed at how massive it is in person but to my surprise it looked very well kept. I immediately sourced a couple batteries so I could fire it up and hear the engine. After several attempts to get the fuel system primed I succeeded and she roared to life. The engine had a minor but noticeable knock as well as severely contaminated engine oil (coolant in the engine oil) and hardly any coolant in the radiator. Somewhat discouraged I parked the truck out of the way until today. This morning I decided I had stared at it long enough and dragged it out of the field to work on it. I pulled the oil pan off and I was glad to see that it didn't have any metal shavings in the pan and no obviously overheated or damaged bearings. I haven't pulled any main caps or rods yet but at first glance the bottom end seems ok. I did notice it has 2 scored cylinders which I believe are the cause of my engine noise/knock. I then attempted to find the source of the coolant leaking into the crankcase by pressurizing the radiator but didn't have much luck. I applied about 12 psi of air pressure to the cooling system before the radiator sprung a leak from the upper tank and started to make creaking noises. I plan to plug the upper and lower radiator hoses to remove the radiator from the equation and apply 15-18 psi to the block and heads. I'm hoping the increased pressure will show the leak. From my research I found the most common issues that would cause this problem are the liners leaking from the lower O-rings or the oil cooler ruptured. Is it possible or likely that a blown headgasket could cause this issue? I'm my experience ruptured oil coolers usually put oil in the cooling system not the other way around as the oil pressure far exceeds coolant pressure. Does anyone have suggestions on how I could diagnose the source of my cross contamination issues? I would really like to diagnose this issue definitively before proceeding with the teardown and in-frame rebuild. I'm hoping one of the experts on here will be able to point me in the right direction.
Thanks!

 

[NDT]

I think you are going down the right path. The water dribble into the crankcase should be very obvious once you pressurize the coolant jackets. My money is on liner orings. Sounds like the engine was run without coolant.

 

[Bandit02]

Possible cracked head(s) that opens up when it's hot. Might as well get them checked if you have it all apart anyways.

 

[WillWagner]

If it has scored liners, that is the most likely issue for the coolant on the oil. When the piston and liner decide to swap material, the lower seals get real hot, bake and crack. They then put coolant in the oil. You need to find out WHY the cylinders scored. Heads don't crack too often unless it was run very hot, scored liners are a sign of running hot. You will be able to see the cracks, if the heads are cracked, between the injector bore and the valves or between exhaust valves. If it were me, I would find a way to pressurize it and look for a leak path. Between the piston and liner is a head or a cylinder, or both, out of a main journal, between the crank and bearing, usually #2, is an oil cooler. Oil coolers usually don't cause scored liners, Look at the w/p, piston cooling nozzles, w/p belt and the radiator, fan drive, t-stat. No stat can cause an overheat issue.

We need pictures!

 

[Southern Krawler]

Thanks for the input guys I appreciate all the help . This forum is a great resource lots of very knowledgeable people willing to help!
Willwagner-initially I suspected the overheating happened when the coolant went into the crankcase and left the heads and waterjackets dry but after attempting to pressurize the cooling system through the radiator I see the truck has several external coolant leaks and I believe it's more likely what you suggested and the engine overheated after being run low on coolant. That caused the scored liners and mixing of the coolant and oil. Your explanation of the liners getting very hot when they were scored and cooking the o-ring seems much more plausible then o ring failure due to corrosion or "lot rot". I will definitely go through the rest of the cooling system to make sire its up to par. I will pressurized the block tomorrow and post my findings. As far as pics are concerned Im not exactly sure how to post on here do I need to host them on another site or can I upload them directly?

 

[porkysplace]

Thanks for the input guys I appreciate all the help . This forum is a great resource lots of very knowledgeable people willing to help!
Willwagner-initially I suspected the overheating happened when the coolant went into the crankcase and left the heads and waterjackets dry but after attempting to pressurize the cooling system through the radiator I see the truck has several external coolant leaks and I believe it's more likely what you suggested and the engine overheated after being run low on coolant. That caused the scored liners and mixing of the coolant and oil. Your explanation of the liners getting very hot when they were scored and cooking the o-ring seems much more plausible then o ring failure due to corrosion or "lot rot". I will definitely go through the rest of the cooling system to make sire its up to par. I will pressurized the block tomorrow and post my findings. As far as pics are concerned Im not exactly sure how to post on here do I need to host them on another site or can I upload them directly?

This link , post # 46 should help on how to upload pictures , load them direct to the site .
https://www.steelsoldiers.com/showthread.php?59917-How-to-post-pictures-a-tutorial/page5

 

[Southern Krawler]

Ok so I performed another block pressure test after eliminating the Radiator from the equation and still no leaks. This one has me stumped. I went all the way up to 22-25 psi and let it sit there for about a minute under pressure and still no leaks. Should I just tear it down and look for signs on disassembly or is there anything else I can do before I rebuild it? I would really like to identify the cause of failure. I can't get the motor up to operating temp with the liners and pistons scored like they are. Any suggestions? Here's some pics as Requested

 

[gimpyrobb]

HAHAHA! How much lift did you get out of the hi-lift jack? I bent mine with it in the same place (on a deuce).

 

[red]

Check the oil cooler. When the engine is shut down after running the cooling system is still pressurized and that's when it forces the coolant into the oil passages. Pretty common cause of coolant in the oil.

 

[74M35A2]

Have heard before oil cooler is common cause. Coolant is like acid to bearing coatings. Leaves them looking like pizza if sucked up by oil pump. Can’t see it until you pull them out, surface check.

 

[Southern Krawler]

Gimpyrob that poor high lift could tell some stories I've had it severely overloaded more then once and it's still going strong. I bent it real bad once in the desert and I straightened it back in my 20 ton press, as you can see it still works pretty good. In total it probably lifted it 4-5 inches. It stopped real quick as soon as the leaf spring stopped drooping. I was tempted to break out the cheater bar but I didn't wanna push my luck and I was able to wiggle the oil pan out .