My reman (20 hrs ago and never run) 401 in my 65 skylark Gran Sport lost some oil pressure after 30 minutes of run time last year, when I checked oil level is was up by 2 quarts! coolant had contaminated the oil. After a second tear and inspection by machine shop they felt a poor machine to the right side of block deck had caused a leakage between the front oil and coolant passage. I replaced main bearings and reassembled with new gaskets (Thank you Carmen Fascoe) and found coolant was still leaking into the oil. After many many hours of extensive testing and a pile of luck I found that the leak was through the cylinder head Bolt #3!(see torque chart) threaded hole in the block, it’s supposed to be a blind hole and not be exposed to coolant passages! I’m aware to seal select head bolts. I found the bottom of the threaded portion in r front of block had opened up into coolant passage. After sealing this headbolt, leak has been eliminated. #3 head bolt passes through oil circuit in the head to feed valve train.
I wanted to share this experience as it was a very costly and damn frustrating experience! Hope it will help if you’ve ever heard of a mysterious leak like this. For your future builds, seal all the threaded head bolts!
