D2-5U water in the pony oil…?

Milky looking oil is the result of water contamination. Lots of possible candidates for leakage. If you believe the heads and top manifold gasket are sound I'd suspect the cooling cross over passage that is part of the sump casting may be your problem. especially if the pony has seen freezing temperatures during it's life or there has been serious corrosion of the water side.

Yes, the big engine coolant gradually drops over time…, I'm certain I'm some how getting cooling system fluid into the pony crankcase. I'm just not familiar with how the cooling system works. I don't see how, or where the cooling system crosses with the pony crankcase that a break or malfunction would allow mixing. My choices seem to be:
1.] cracked pony block…

2.] cracked pony head…

3.] blown head gasket…

4.] damaged pony manifold gasket…

5.] now perhaps Old Magnet has came up with some where else I could be having a problem… I don't see exactly where you mean O. M.
Where would this cross over passage be? In the sump casting? Would that entail splitting the engine-clutch-transmission and
replacing/repairing a crack. Oh My! As bad as that sounds, Oh My! This tractor has certainly seen some colder temps. that's for sure.
It was born in Illinois, raised in southern Montana and northern Wyoming for 60 some years and if I'm going to have them use it to cover
me up, I'm going to have to fix it!

I guess I'll start with the easy things first….

The cross over passage is cast in to the pony block....the rectangular section you see at the bottom of the block. Water comes in from the bottom, flow is split to left and right head, up through the top manifold and back to the main engine.
This would be the last thing I'd check but you seem to be convinced everything else is fine.....yet you still have a problem.

Hummn, Yeah you've got it O.M.
I'll just start looking from the top down…., I'm actually not convinced every thing else is fine. No. I am just WISHING every thing else is fine. I know,"Wish in one hand and poop in the other. See which hand fills Up first!"
I have another pony motor off of a parts cat. It didn't run but if I find something wrong in the pony that's on my D2 now, I can hopefully have enough parts to,'Make one out of two…'
I can't believe the experience you have with these CAT animals. What is your background? If you were in the construction, mining, or farming industry, they/we surely have benefited from your knowledge. Thank you!

p.s. I hope when I'm done fooling around with this D2 that the darn thing runs as good as it does now, only without the [u]coolant in oil[/u] problem…, Ha ha, Git'ter done!!!

Thanks again...

Just thought of something else…

Thank for the pictures O.M. , Did you just happen to have a pony torn down on your bench? Or, are the pics from your vast store of experience?

I'll try to take pictures of this little project of mine so someone else will maybe benefit…

Again, Thanks again!