283 leaky after highway run (long)

[xaircav]

The '62 283 in my '53 3100 will drip a few drops of oil after a run around town but after an extended highway run (75-80 MPH at 2500 RPM) it will leave a puddle about 4" in diameter. The engine has 8000 miles since the rebuild and has always done this. I run a PCV from the road draft tube hole to the carb and an intake with a fill tube and breather. The factory vapor can in the lifter valley is in place. My theory is that at highway speed when vacuum is low pressure builds in the crankcase and pushes oil out the rear main seal. I've ordered a road draft tube and mounting kit and will report the results. I'll bet the pic is upside down.