Is there a definitive way to diagnose a cracked head vs. head gasket

Greg? IF you're getting water/ antifreeze in the oil, it's time to do something about it. As far as diagnosing whether it's a cracked head or a blown gasket, I don't know how. .maybe someone else does. Are you getting bubbles in the radiator filler when it's running? And maybe a trace of oil/ fuel in the radiator? By your description of the oil level rising, it's also probably getting gray or white. .that's water in the oil😮 . Either way, it's time to take the head off and check. .hopefully it's just a head gasket and not a crack in a cylinder wall or a cracked head.

Greg? IF you're getting water/ antifreeze in the oil, it's time to do something about it. As far as diagnosing whether it's a cracked head or a blown gasket, I don't know how. .maybe someone else does. Are you getting bubbles in the radiator filler when it's running? And maybe a trace of oil/ fuel in the radiator? By your description of the oil level rising, it's also probably getting gray or white. .that's water in the oil😮 . Either way, it's time to take the head off and check. .hopefully it's just a head gasket and not a crack in a cylinder wall or a cracked head.

You need to fill it to top again and watch see if it bubbles . If water is going to oilpan then the oil will turn milky colored and if precup are ate thru or coppers are bad then youll get fuel floating in rad.if Sounds to me like maybe the therostate open and filled some viods with water and the oil got warn and expanded. But as for your orig. quest. if its head gasket it will bubble the same hot or cold a crack will get worse as it warms up, Fill it up to rim watch for bubbles and or black soot and oil coming to top

Hi Dunefanatic,
just possible it may be caused by an air lock in the pony engine cooling system, see the att. scans relevant to bleeding air out of the vent cock on top of the pony manifold.
Hope this helps.
Cheers,
Eddie B.

gaining oil is most often due to fuel dilution.

I can see some thermal expansion or aeration of oil raising the level slightly while running, so check carefully after it has cooled off or something to make sure what you are measuring.

On my D2-J series, the manual says to check the oil level running because when you shut it off, oil may/will drain back from the oil cooler into the crankcase. I agree that it would be milky if the crankcase had water in it.
You can go to your local automotive repair shop and buy a kit that allows you to put a base sample of your crankcase oil in it and a sample of your suspect oil to send out to be tested. It costs about $25 or so. Cheaper than taking off a head.
I had alot of trouble with mine blowing water until all the Prestone radiator flush cleaned the rust out of the engine passages. Then we got the air purged out of the pony and the engine block. The level has been fine since.
drujinin

As I recall, Greg's 5U is direct electric start.

If your head is cracked,blown gasket,low liner,precumbustion chamber pitted,loose or a cracked cylinder liner that would allow hot compression to leak into the cooling system and it would overheat very quick,it is possible that the seals on the bottom of one of the cylinder liners is leaking,that would not cause slobbering or overheating just coolant loss and the oil rising,next time you park up fill the rad full,when you come back to it check if the level has dropped and top it up again to see how much it takes,if it more than a pint it must be going somewhere,before you start the engine undo the sump plug and drain off a quart of what you will be hoping is oil,if there is coolant in it you should see it,if you find no coolant look for an external leak water pump, rad and hoses etc,see if the oil smells of diesel fuel or is diluted as that may be the cause of the level rising.
AJ