2cyl kubota - help narrowing down cracked block/head/or? Coolant in oil, zb400 horizontal zb600 12hp diesel

[rice_harvester]

Small belt drive tractor with kubota zb400 (zb600 more common, similar) runs surprisingly well but after only 30sec or less of running the oil is way over filled & milky. When not yet running, coolant doesn’t get into oil. The coolant system also had some signs of significant oil residue.

Unknown previous history so could’ve easily been left over winter with straight water.. Or overheated etc

Pulled the head but unfortunately didn’t attempt any coolant sys pressure testing beforehand.

No outward signs of cracks in head or block at all. (Or other visible issues). The headgasket did deteriorate significantly (bottom center area) when I pulled it off BUT no signs of combustion gas in cooling system, or other related hg symptoms. Once apart, I’ve blown compressed air through every passageway & couldn’t come to any conclusions.

Thermosiphon, no water pump- it pretty much has to be a cracked head or block-right? Or am I missing anything....

I’m hopeful I can further troubleshoot rather than haul it to a machine shop. Anyway I’m thinking my next step is either to:
1) buy misc rubber plugs/etc & attempt to plug most/all passageways, while continuing with compressed air to narrow it down.
2)Put it back together & pressurize coolant system from the top. I’m thinking yamabond or copper gasket spray on the delaminated old head gasket as I’d hate to ruin a new one.
ANY input would be VERY greatly appreciated

 

[mrmikey]

A cheap way to check for cracks, not always successful mind you but worth a shot, clean both head surfaces off and spray some penetrating oil on it, wipe it off good with a clean towel and shake some talcum powder on it and let it sit for awhile. The talc will draw to a crack as the oil and/or antifreeze will wick out into it. There are commercial dye penetrant test kits around but this is a cheap version. You could always go to a machine shop and get it magnafluxed.........M

 

[BeezFun]

Did you happen to remove the radiator cap when the engine was hot? I would expect no or very little pressure in the cooling system with a thermosyphon system, which makes it hard for water to find its way into the oil. But if the head or head gasket failed in the right spot, it could pressurize the cooling system and that might force coolant into the oil. Is there any reason you don't think it could be the gasket?

 

[rice_harvester]

Thanks so much for for the input & encouragement, (more troubleshooting steps to do now & likely more pulling apart I suppose.. time to see if I can get a better view/understanding of the block & passageways with more of the covers and parts off)...

I agree hard for water to make it into cooling system in most normal situations as oil is under much more pressure. I'm experienced spotting head gasket issues and symptoms in larger engines/vehicles - and I did run it for a minute with the top radiator (as well as cap also) off to look for combustion gasses (bubbles) in the coolant system- no signs. Also after pulling apart, before cleaning surfaces/etc, I examined the "coloring" & residue /etc around the headgasket and in the cylinders. Found no "discoloring"/traces that might indicate a blown headgasket nor signs of water getting into the cylinders themselves. This model also has an abundance of head bolts for the size! Also forgot to mention I checked block and head with a straight edge, nothing abnormal there.

Additionally, the amount of coolant making it into the oil in such a short period of run time (say 1.5-2 quarts overfilled after only 20-30 seconds running, with a 2qart oil capacity) seems to be a lot to have been coming from the headgasket alone without obvious signs, but I'll be the first to admit I'm no expert on small diesels.

Again this is an engine with the cylinders horizontal (like half a 4cyl boxer engine) so it seems at least a possibility that it might be more susceptible to cracking water passages (freeze damage with straight water) in the "lower" side of the block, vs a vertical engine.

The head is small and I did go the rubber plug (and block/clamp) route for some initial testing on the head already - I feel like I've done a pretty good amateur job of plugging all the coolant passage holes and blowing upto say 60+psi through most passages/ with no obvious air leaking out where it shouldn't be. So I'm ready to move on to checking the block (as best I can) next.

I don't exactly have a small diesel engine guru shop around locally and most of the automotive or agricultural shops I know of ---the machine shop rate (in this area) for magnaflux testing would be the same ballpark cost of a used engine (transit shipping time considerations aside)- , so I'm hopeful I can at least have it narrowed down before I bring it in or pursue that route further.

Thanks again!

 

[BeezFun]

Please post when you figure this out, it's a puzzler. I was thinking of other things that might be involved. Does it have an oil cooler? How is the crankcase vented? It's hard to imagine any way either of those could cause enough pressure to get that much water in the oil.