RickR

I'm building up from a bare block Gen VI 502

I've searched the OSO for info on the bypass valve (or plug) mounted on the surface of the oil filter adapter boss next to the threaded nipple.

How about the other bypass valve that is recessed in the passage above the nipple. Looks like it goes to the upper part of the block and lubes the cam and lifters.

What is it for?
Why would you restrict oil to the upper block with HYD lifters?
That valve in my 454 MAG has very light spring pressure,
would the 11# valve be best there?

blownboat

I believe the valve under your oil filter is only for safety measures in case some one doesn't change their filter and it gets plugged. That valve will open under pressure so at least you are getting non filtered oil in the block. Alot of guys take it out and tap it and put a plug in it so high volume and high pressure oil pumps don't cause it to open. The other plug is only needed if you plan to run an external oil cooler. If you dont have that valve in there I believe the oil will discharge out both ports stopping in your oil cooler. The valve stops 1 direction and allows it to run through your external cooler! So if you plan to run an external cooler you need the valve.

blownboat

I just looked in my mark vi big block book. The part numbers are ac delco 25013759. You need 2 of them. One under the filter threaded adapter and the other one next to it on the flat surface. The part number for the oil cooler bypass valve is gm 5575416.

bobl

You need to use a 30# bypass valve, pn 25161284 located on the filter mounting pad. Do NOT use the valve in the center when using the normal marine remote filter setup. This valve is only functional when you use the threaded holes by the oil pan rail for the remote cooler. These do not supply enough flow for a marine application and are normally not used.