Re: Coolant leaking into oil, water pump issue or worse?

Posted by Fish'n Jim On 2020/12/10 10:15:42

If it's had water in the oil and run or sat for any length in that condition, you're in for a big repair, not just a water pump rebuild. Hopefully you drained out that wet oil already.

Didn't say what year/motor, but guessing, the straight flat heads are notorious for siamese cylinder design and large head gaskets that leak. Boring/decking can make it worse. Lots of posts on here.
We all expect a rebuild to be done and done properly, even by experts, but sometimes thing go unnoticed or undone. I recommend a test stand or dyno run before acceptance. It's cheap insurance another level of reducing error.
But just a guess since from way afar and defer to Ross.
Sorry for bad news. I think the compression test at this point is moot [One could also pressure test the coolant side.] - confirms the obvious and delaying the inevitable. It's leaking and won't know where til it's torn down and inspected.
Unless it's unintentional, someone put water in the wrong place. I had an aunt that put oil in the radiator overflow because she "knew" it took oil but didn't know where to put in since deceased uncle did those kind of things.