So the MTVR adventure begins

[aw113sgte]

Productive day today since it warmed up to the 50s!
Primary and secondary fuel filters changed. Hand primer seems to have an issue though, seems the check valve isn't working as I can see it push the fuel but then suck it back with each pump. Will pick up a new one tomorrow.

Transfer case fluid changed. Hard to find 40w engine oil but got some royal purple synthetic. Tried the harbor freight electric pump but found out thick oil doesn't agree with it. Unsurprising for $10. Just used the old hose and funnel method. There were some very small chips on the magnet, no idea if it's been cleaned before. Oil coming out looked great, still golden.

Serviced the after cooler (with the exception of the outlet valve...need to find or make a tool for that wierd hex fitting). Kind of a pain and easy to cut o-rings when putting everything back together so be careful and lube those things. Pretty sure this is the exact same unit as used on early FMTV vehicles, but they use the dessicant version- the instructions even said dessicant and didn't have any notes about the aluminum filter units. The aluminum filter pieces looked new, the lower filter rubber was degraded and falling apart. Took a lot of time cleaning out the oil/water junk, not that there was too much.

 

[aw113sgte]

Used some choice words when I took off the oil filter and bright green coolant spilled out. Truck has been great and then I find this. I've done previous research on the c12 and am aware of some weaknesses from overheating and cracking heads. Maybe a liner is cracked, maybe the block is? Headgasket?
They also have a weakness with the water pump and considering how fast this came on that's my best guess. I'll be doing some diagnosis with a coolant system pressurization tool to find out the issue. It could be the radiator/coolant cooler. Maybe someone pored coolant in the oil fill (doubtful). I'm going to pull the front oil drain plug and snake a camera in when pressurizing to try and locate the leak. Fingers crossed it's something I can easily fix.

 

[IridiumRed]

Ughhhh about that last photo. That ranges from not-good to potentially really-bad.

Have you drained the crankcase yet? You really should if you havent. Ive read that coolant in the oil mixes with combustion byproducts and makes a low grade acid that is corrosive to bearing material, particularly rod/main bearings. Id want to get that coolant flushed out of engine ASAP before it does any damage / limits whatever damage has been done. At least dump crankcase, can shove camera in there easier wo oil too... decide what to do from there.

Best way togetthe remaining coolant out of crankcase is putting in new load of oil and running for a bit / draining, but that doesnt do much good if you still have leak, that just dumps more coolant into the oil...

Big question where it is coming from. I think pressurizing system / getting camera in there is best plan. Heck, just pressurizing system and letting it sit for a short bit and checking to see if pressure falls is best way to check that you do in fact have leak (if she doesnt leak down at all, then it COULD be someone poured coolant into oil... but unfortunately i think the odds of that are low... be nice if thats what it was... (or at least a little nicer).

Places to look, yes liner area would be good. Look around water pump area. C12s losing water pumps (bearing seals go out, start puking coolant.. if weep hole gets plugged it can dump into crankcase... and im not sure that they cant puke into crankcase wo a plugged weephole as well, that last part is just a guess off the top of my head, the plugged weephole causing leak into crankcase is a known c12 issue).

Another POTENTIAL source for leak is the oil cooler. Im not sure the C12 is setup in a way that makes it likely, am speaking from general diesel engine knowledge here (ie, other diesels that i often work on can have this issue). Its just a common area for potential issues when you have pressurized oil/coolant being shoved into same area, only separated by seals and thin tubing. I believe theres 1" NPT plug on end of cooler, might be able yo shove camera in there and see at least half of the cooler (see that end... whether you vould see other end would depend on camera size... though there may be plug on other end you could put cam in as well, have yo think for a minute on that)

Is there any evidence of oil in the coolant?? thats a very good piece of information in situations like this, if there is a place where pressurized oil meets coolant, a blown seal, crack, whateverthat lets them meet, the oil tends to get forced into the coolant while engine is running. Then, when rngine is off, coolant might creep into oil (due to being thinner and heavier). No oil in coolant would -tend to- indicate the leak doesnt involve a leak between pressurized oil and thd coolant system. Can -help- narrow down the possibilities.

Damage due to overheating (which could cause liner seal to go maybe), but worse could mean cracked head... is concerning. C12s are known to crack heads... lets hope its not that.

One thing that might REALLY help you out is that the coolant leak MIGHT be new. These trucks often sat a long time wo running, lots of things can happen from that. Can get corrosion on surface of journal that a seal runs around (like wster pump). Get rust spot, that when engine is fired up, slowly starts eating seal. Or have seal start dry rotting, have it start disintegrating when engine is run after long time sitting. Theres multiple scenarios where engine only starts leaking after long period of sitting.

If leak is new, that would be great news for you in terms of damage from coolant in oil. Thats time / use based. If leak just occurred and youve only run her a little bit maybe no damage done. Thats best case scenario, letshope for that

One other thing - have you noticed change in coolant level?? Ie, have you been watching it / seen it fall?? Could give idea on severity / how long its been there.

If i had to take a guess, i bet its leaking water pump. One nice thing id you can buy all the individual pieces, parts, seals for it from Cat. Theyll bend you over for s whole new pump, but being able to just order some seals and fix specific problem is nice (and way less $). The C12 water pumps are setup totally different then wster pumps for a lit of smaller diesels, the C12s can be taken apart into many smaller pieces. If you look at the water pump dection on Cat Parts you can get good breakdown of what parts go where / how it works overall. If need be i could probably find you breakdown of that as well, ive certainly seen it, just dont remeber exactly where at moment (could have been in 3 or 4 different places, not sure off top of my head)

Anyways! Good luck w everything. Keep us posted on what you check / what you find. Im happy to help in whatever way i can, just let me know if i can...

 

[IridiumRed]

btw, for whatever its worth, i have a spare used C12 water pump + seals + some assorted hardware. Not for sale, am keeping as spares, but if you want any photos I can provide if you let me know what you want to look at.

My MK25 had a coolant leak from water pump area (fortunately it was just EXTERNAL leak) bought a bunch of stuff so i could repair it, turned out didn't need it, was just leaking hose (almost impossible to see), but I like having spares around anyways, it my mind having a seal go out on oil cooler, water pump, etc is more of a "when" thing vs a "maybe" when dealing with a truck as old as this.

But if its useful to see some components while not-on-truck let me know.

 

[aw113sgte]

I'm going to pick up a coolant pressure tester today, along with a gas byproduct tester.

I've barely driven the truck - only a few miles since unloading. Coolant went down a lot from when it was delivered so this seems like a new and rapid leak.

I did drain the crankcase - absolutely no coolant came out (I did that before the oil filter). Looked exactly like regular engine oil. No evidence of oil/water sludge mixture on dipstick or anywhere else. Seems odd there wasn't any in there. Almost like it's just been leaking directly into the filter. I'll double check the drained crankcase oil though as I have it in a separate container.

I'm going to try and get the front drain plug off and snake a bore camera in there for the pressure test to see if it leaks from the area near the water pump. Also going to pull the oil lines from the radiator and see if coolant comes out of those.

 

[IridiumRed]

Btw, I was thinking about this while looking at my truck this morning, and if the oil cooler leaked, it could potentially run coolant right down into the filter. Oil cooler is RIGHT above the oil filter module, which holds a bunch of valving.... and the hookups for the remote oil filter. If there was more room, you would just have the oil filter mounted right to that, but there isn't, so they run lines down to the remote filter.

But I bet coolant could go right down into that module, and then run right down the remote oil filter lines. Coolant is heavier, so it would displace the oil, and could all pool up in the filter.

Where 15-16 is in the following image, you can pull that plug and put a camera in there, and see one end of the oil cooler probably (this is on the oil side so if you have coolant system pressurized you should see air blowing out).

Right above this, connected by vertical pipe, would be the oil cooler. On the other end of the cooler, but on the oil cooler housing itself, is a 1" NPT plug that you can pull and see the other end of the cooler. Its on the coolant side, so pressurizing cooling system it might not be as obvious if you have leak there (since you'd be on the side blowing the air instead of receiving it) but I bet you could still see -something- probably.

Of course, you can always run air pressure through fitting 15-16, that will pressurize oil system a little bit, but will be hard to see leaks because the oiling system is SUCH a high volume flow (49gpm at 52 psi at 2100rpm...) and air flows a lot easier then oil too, so you need a TON of air flowing through system to find oil leak (I know this because I messed around with that some, trying to diagnose stuff on mine)

Anyways, just from what you've said above, I feel a lot more optimistic about the outcome (since it sounds like leak was just recent... truck hardly run... and sounds like it hasn't really run with the oil and coolant mixed since no sludge....)

 

[IridiumRed]

Oh, just for sake of completeness, in above diagram A is where the oil filter remote housing bolts to. C is where you could mount a secondary oil filter (for finer filtration, a bypass filter), if there was room (and there is no room on the MTVRs... way too much stuff in that area)

Where C is, theres a cap on it to block it off. Its simply a square drive (3/8" or 1/2", dont remember). it just unscrews, std RH threads. One thing you could do is pull that cap and look in it to see if there is coolant in there too, theres not a lot of room in the cap but a little bit, and its a dead end as well, if something ran in there, it probably can't run out. I'm GUESSING that if the front of the oil cooler leaked, it would put at least a tiny bit of coolant in that cap. Also, i'm GUESSING that if the rear of the oil cooler leaked, it MIGHT be able to put coolant in the oil filter w/o getting any in that cap. I wouldn't count on that 100% at all, but whether or not there is coolant in that cap might just tell you which end of the oil cooler is leaking....

Anyways. good luck

 

[IridiumRed]

Btw, heres a pic of the oil cooler, one of seal #9, I think thats where you may be getting coolant in the oil. Those go to oil filter module right below it. Also, #19 is the 1" NPT plug you could pull, stick camera in

 

[aw113sgte]

@IridiumRed Thanks so much for all the info, gives me some great resources to reference.

 

[IridiumRed]

You're welcome. Steelsoldiers has been great for me, if it wasn't for here, I probably wouldn't have any military trucks. And I really like military trucks Mostly just read posts here, lots of times dont feel like i have a lot to contribute, so I try to help when i can

I do know the oil systems pretty well on these trucks, really do need to get on doing that writeup of how they work. Will soon.

Anyways!

Something else I thought of, the way the oil pump is positioned, if coolant ran down into the oil filter module (which then drained into the filter, as you know), on the other end of that module (below fitting 15-16 in diagram), thats the outlet for the oil pump. If a small amount of coolant went down into the oil pump, say a cup or two, i'm not sure it would run into the crankcase.

Btw, in this diagram #7 is the vertical pipe connecting the oil filter module & the oil pump (#14 and 15 point to components within oil pump)
Right above that vertical pipe is the fitting you can pull to get access to oil passages / put camera in (and, if you ever want to use external pump to prime oil system, this is perfect place to feed it, its how i do it)

Anyways, theres a chance some coolant could get trapped in oil pump assembly/piping, might be worth pouring some oil into the fitting mentioned above, try to get it to go to oil pan (course, could probably run the camera DOWN through that hole, see if you can see any coolant down there, it will definitely stand out color wise). letting the engine crank for a few seconds would probably take care of it too, kicking any remaining coolant out (probably with oil filter unhooked, outlet ports covered...). Using air hose on that fitting to just blow air through would probably move the coolant too. Just double check oil pan, make sure whatever is in there comes out... because some of this might throw the coolant into the pan

What i'm trying to avoid here is the scenario where say, you find leak in oil cooler, fix that.... then fill system with coolant and oil... then discover you still have -some- coolant in the oil.... which can still damage things.... and, can certainly make a person worry!

 

[aw113sgte]

So I think I got really lucky. No evidence of coolant ever reached the motor. Seems like something failed after I parked it and I just decided to change the oil at the right time.

Pressurizing the coolant results in a steady drip of coolant out the oil filter base (it was dripping all night with no added pressure too). Need to find out the flow path but I think its the cooler assembly on the block @IridiumRed noted above. Had the oil pan plugs out and there was no coolant that drained in the crankcase. Pulled the oil cooler lines in the radiator and no coolant pushing from there. I can't really see where the line with the coolant in it goes. I'll need to take some rubber shields off and get a better look when I have some more time. I also saw a leak from what I think is the coolant hose from the pump. Looks like that will be a bit of a pain but will probably be in there anyways.

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Second leak:

 

[IridiumRed]

That external leak, mine had a leak in the exact same place. Turned out one of the hose clamps was loose! Tightening it solved the leak. If you have to replace that hose, its some work, i believe the oil cooler needs to be pulled off to get room. And there are lots of seals involved with that.... i'm glad i didn't have to do that on mine. Of course, it sounds like you need to pull oil cooler anyways and reseal, so, that actually makes replacing that hose easy

So far so good on your findings, i'm guessing you did get pretty lucky. Also, i'm betting that its the rear end of the cooler thats leaking, if the front was leaking, I think it would have run into the pan at some point (with a constant dripping leak). Butttt.... i dont know if it matters much which end is leaking, once you're in there, just do both ends

Also, there are some vertical pipes that connect things, like between the oil filter module and oil cooler. One Oring on each end of each pipe. I think it would be really good to have those, replace those, while doing oil cooler job. I sure wouldn't trust 20 year old truck orings to get pulled apart, moved around, and then go back to sealing.... just bumping stuff like that make a leak. I had those on hand, was planning on resealing cooler, just turned out I didn't need to.

Anyways, i think those extra seals are worthwhile (and I wouldn't dive into a job like this w/o them.... would hate to have to do all of it twice because of tiny seal that I could have changed with a few extra minutes while i was there), but thats personal choice. But I will say, when looking at "seal kits" for oil cooler... I dont think those were included (or maybe 1 end of pipe was included, but not the second end....). I just looked up on cat parts online, and ordered by part #'s... I just remember having to add in several things to order, wasn't just picking a premade kit and rolling with it (for everything)

 

[fukiphino]

This is all really good info thanks for sharing! I'm about to be in the same boat, mine just started a big coolant leak after 24 hours of driving. I hope it's just some old seals.

 

[IridiumRed]

Where is it leaking??

And, i might be able to put together a parts list for what i think the oil cooler seal replacement would take... at least pick up the extra seals that i think might be needed, if anyone wants

 

[aw113sgte]

That external leak, mine had a leak in the exact same place. Turned out one of the hose clamps was loose! Tightening it solved the leak. If you have to replace that hose, its some work, i believe the oil cooler needs to be pulled off to get room. And there are lots of seals involved with that.... i'm glad i didn't have to do that on mine. Of course, it sounds like you need to pull oil cooler anyways and reseal, so, that actually makes replacing that hose easy

So far so good on your findings, i'm guessing you did get pretty lucky. Also, i'm betting that its the rear end of the cooler thats leaking, if the front was leaking, I think it would have run into the pan at some point (with a constant dripping leak). Butttt.... i dont know if it matters much which end is leaking, once you're in there, just do both ends

Also, there are some vertical pipes that connect things, like between the oil filter module and oil cooler. One Oring on each end of each pipe. I think it would be really good to have those, replace those, while doing oil cooler job. I sure wouldn't trust 20 year old truck orings to get pulled apart, moved around, and then go back to sealing.... just bumping stuff like that make a leak. I had those on hand, was planning on resealing cooler, just turned out I didn't need to.

Anyways, i think those extra seals are worthwhile (and I wouldn't dive into a job like this w/o them.... would hate to have to do all of it twice because of tiny seal that I could have changed with a few extra minutes while i was there), but thats personal choice. But I will say, when looking at "seal kits" for oil cooler... I dont think those were included (or maybe 1 end of pipe was included, but not the second end....). I just looked up on cat parts online, and ordered by part #'s... I just remember having to add in several things to order, wasn't just picking a premade kit and rolling with it (for everything)

Oh yeah I'm for sure on the side of replacing every seal I touch when doing stuff like this. Hoping for a seal, but could very well be the heat exchanger itself...pricey.

 

[IridiumRed]

Where is the leak? internal, external, where do you see evidence, etc?

EDITED TO ADD - i meant that in response to Fukiphino, got lost in the thread

Yeah, for your sake I hope its the seals too. When it comes to coolers on other vehicles, my experience has been its the seals that go first... usually. And the seals are way cheaper than the rest of it, and you have to pull all of it off anyways (whether you are replacing seals or the cooler itself), so once you get it off you have a lot better idea whats going on / what the condition is like

 

[aw113sgte]

Makes me wonder why the truck has two oil coolers? Guess the CAT on on the block wasn't enough so they added the additional one in the radiator? Actually...the radiator one may(probably is) a transmission fluid cooler.

 

[IridiumRed]

i hadn't seriously studied it, but i thought the radiator heat exchanger was for tranny

 

[fukiphino]

Where is it leaking??

And, i might be able to put together a parts list for what i think the oil cooler seal replacement would take... at least pick up the extra seals that i think might be needed, if anyone wants

I think it's the water pump, but haven't been able to locate the exact spot yet. For how big these trucks are the engine bay is pretty tight, not the mention everything is covered in rubber guards.

 

[IridiumRed]

Partly thought that because on a truck like this, i'd EXPECT to see some sort of external transmission cooler of some kind, having the tranny run all buttoned up is a ton of heat to displace (with an automatic tranny anyways) and a radiator heat exchanger is so common...