1990 Scrum F6A engine Original issue was oil in coolant. Suspect was oil cooler- deleted that. Rebuilt engine, inspected and all else looked good. No signs of oil into coolant passages. Back together - run well for a few hundred kilometers, then got oil in coolant again. No coolant in oil. Pulled head, lapped it and got it good and flat. Installed same size restrictor in block that is in the head- to keep oil pressures on the block/head junction lower. Runs fine, but I think I’m getting oil in coolant again. Still no coolant in oil. I will pressurize coolant system and see if any leaks, and verify it is new oil and not just some leftover. Ideas? I’m down to head or block cracks. If just head- that would be ok, but I also do not want to blow a bunch of money and time and find that doesn’t solve it!
I pressurized cooling system. It very slowly drops. I do not see any leaks (but of course could miss a small one like that until closer inspection). I used borescope and saw no signs of coolant into cylinder (I didn’t really think there would be). I have not run it again to see if any water got into the oil. (I just have distilled water in it right now). Sure wish I saw something definate.
Decided to get a good used engine. Once swapped, I will take apart this one and pressure test head- then magnaflux block (after careful inspection of course). That way will have a usable truck- but perhaps a rebuild engine for sale later.
