My new to me reman (20 hrs ago and never run) 401 in my 65 skylark Gran Sport lost some oil pressure after initial 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) that threaded hole in the block, is 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!
