I read about putting a 1/4" pipe plug in there, to disable the oil filter bypass. I added a thermostatic "sandwich" adapter, and an oil cooler. While it was apart, ,I plugged the factory bypass.

I've put about 2 hours on the car since then. A couple days later I noticed about 1/2 quart of oil on the floor. It really seems to have come out from between the filter, and the sandwich adapter. The filter is tight. Would the plugged bypass have anything to do with this? I really don't see how the adapter could be the culprit. It has o-rings, and uses the oil filter's gasket too. It's all tight. :confused:

Should I re-enable the factory bypass?

I'd leave the bypass plugged, change the filter and check to see where it's leaking.

Verify that the oli filter adapter is also tight and clean between the block and the oil filter adapter .
or the old filter "O" rubber ring may be is still on it place with the new one this can cause the leak between them to .

With a plugged bypass, a restrictive fine filtration filter, thick cold oil and a bit too much rpm, you could well have some excessive pressure issues on cold start-up, assuming that your oil pump's relief valve can't flow enough to keep things at the relief valve spring pressure.

When running a plugged bypass, it is wise to run a low restriction/racing filter, thinner oil and go easy on the rpm until oil is up to temp. That way you don't have any concerns about over-pressurizing anything during cold start-up.

I'm setting up my 540 with a plugged bypass as well, but I'll be running a Moroso high flow/low restriction oil filter and Royal Purple 5W30 Racing oil.

The wierd thing is it was after my drive that it leaked. And there's no evidince of it leaking while I was driving, the bottom of the car is clean. There was a little trace of oil thast appeared to come from the oil filter gasket on the filter itself, and dripped down the filter making the puddle on the floor.

I'll have to take the filter off later I guess, to see if the adapter is tight. I'm 99% positive that it's on tight, as I can't rotate it at all. The filter itself, is an AC delco PF1218. Is that too high of a restriction for plugged bypass? I was using 10w40 conventional valvoline. Oil pump is a summit pump, with the high pressure spring. Pressure is a little over 60 cold. The engine does see 6500+ rpm occasionally, and with my gearing - about 4000 rpm highway cruise rpm. Is this too much for my oil and filter combination? The track is over an hour away... I'd hate to empty my crankcase on the way there :(

you could check and ensure the head of pipe plug you installed isn't interferring with anything.

Update:
I took things apart.... It was definately leaking at the oil filter gasket. I replaced the blocked bypass with a stock functioning bypass. No more leaks. (yet, anyway.... :) )

Aparently 60+ psi is too much for a PF1218 and valvoline 10w40, with a blocked bypass.

I ran 80+lbs.cold(too much) with 10-40 and a PF1218 and also had a blocked bypass on my 461. Never had a leakage issue but definitely let that engine warm up when you start it cold before you get on it.