Unusual coolant in oil/oil in coolant issue

[Heavy foot]

Hello oil burners, this is my first post and I want to start out with thanking everyone on this forum for all the guidance I have used in the past on here, it really is a great resource for these old diesels and it’s saved my a$$ a few times.
I have a 94 turbo 7.3 idi that had a fluid mixing issue when I bought it, Oil in rad and coolant in the oil. Everything I read pointed to a leaking oil cooler so I replaced the seals and gaskets, lots of flushing later it became apparent that I still had a leak. Winter was on my doorstep and I didn’t feel like laying in the snow and redoing the oil cooler job also another 94 f250 ended up in my driveway so I drained the coolant swapped the oil and parked it for a few years. Fast forward to this year, I’m starting the process of a diesel swap into a 93 gas crew cab and I figured I could redo the cooler seals and have a motor to use. Unfortunately I didn’t drain the block completely and when it froze it pushed the rear frost plug above the cooler and the block heater, I plugged up the holes for testing and ordered some cooler seals and gaskets, Just for curiosity sake (and to burn some time while I waited for seals from Russ repair) I made a pair of block off plates to test the cooler and it held air in the oil side overnight, so I turned my attention to the motor and used the same plates to block off the cooler ports. Put about 15psi in the empty coolant system and within 5 minutes I’ve lost pressure… is there anything else anyone is aware of that can cause a fluid mix other than the oil cooler? There isn’t any external coolant leaks and the motor starts and runs great so I don’t think I have any pin holes in the cylinders. Any help would be great and thanks for your time

 

[KansasIDI]

h e a d g a s k e t

 

[Clb]

Your pressure test proves you have a leaking seal in the block, no longer a cooler issue.

 

[IDIBRONCO]

I doubt that it's the oil cooler. Before you pull your hair out trying to find a leak on the engine, redo the block test except this time, keep the air pressurizing the engine. Not more (higher) pressure, just constant pressure, as in leaving an air hose hooked up to whatever you use to pressurize the block or cooler when you do the test. Then, with constant air pressure inside the cooling system, go over EVERYTHING that's a part of the cooling system with a spray bottle filled with soapy water. That way, you can will see bubbles if there's an external leak. Keeping the air pressure constant will give you more time to do the checking. That way, you can see if your quick pressure drop was from your leak, or from something external that wouldn't cause the fluids to mix.

 

[Heavy foot]

Thanks guys I’m hoping it’s not a head gasket but I’m sure I’ll find out soon enough, I’ll try the constant air test tomorrow and see what I find, I’ve already gone over most of the cooling system with soapy water but I didn’t have a ton of time today, maybe I’ll find something tomorrow

 

[Clb]

Next step..
Old school leakdown check.
Using the same setup.

Listen in the intake for hissing = intake valve ,or manifold leak.
Exhaust port/tailpipe = Exhaust valve
Dipstick = rings

I'm betting on an inside leak.
Only a few spots in the system that are touching each other and can transfer...

Eta
Uv dye maybe...

 

[Heavy foot]

Today I pressure tested again, checked all the exterior cooling system with soapy water and found no leaks. Drained the oil and could hear a small hiss of air through the drain hole, I can also barely hear air leaking at the oil fill. So definitely leaking inside the motor, any ideas where the oil and coolant can transfer? I’m under the impression that there is no oil pressure at the head gaskets but definitely not ruling out the possibility of leaking head gaskets yet. I’m going to study the service manual and some what I can find

 

[Jesus Freak]

Could cavitation be so low in a cylinder that it wouldn't hydro lock?

 

[Heavy foot]

Could cavitation be so low in a cylinder that it wouldn't hydro lock?

I’m wondering the same thing, that wouldn’t explain the oil in the coolant though. Unless I have a few different leaks, I dont have much history on the truck before I bought it

 

[Clb]

Oil feeds to the rockers thru the heads
?no?

 

[Clb]

Cavitation is not gunna show oil in coolant much.
As she will wet the bed first.
Compression will get into the crankcase and vent to atmosphere.
The FIRST perforation you might maybe see some serviceability, not for long tho...

 

[Heavy foot]

Oil feeds to the rockers thru the heads
?no?

The service manual I have doesn’t show the head or block outline in the oil passage diagram but it looks like the rockers are oiled through the push rod as far as I can tell

 

[Clb]

Hows it return?

Thru the head gasket into the block/ valley...

 

[Heavy foot]

Hows it return?

Thru the head gasket into the block/ valley...

Yes there is return oil through the head gasket but it’s not under enough pressure to get into the coolant from there, it is possible the coolant could get into the oil with a bad head gasket but I’m not sure how close those passages are

 

[IDIBRONCO]

Could cavitation be so low in a cylinder that it wouldn't hydro lock?

Cavitation is not gunna show oil in coolant much.
As she will wet the bed first.
Compression will get into the crankcase and vent to atmosphere.
The FIRST perforation you might maybe see some serviceability, not for long tho...

I can think of one possible scenario where it could happen. If the hole was below the lowest point of ring travel in the cylinder, then maybe. Although I can't see where this would cause oil to get into the cooling system. I'm afraid that this is starting to sound like a case where you should tear the engine completely apart and have the heads and block magnafluxed. I hate to say that, but that's where I'm at. Hopefully some genius can come up with another solution.