Results of changing oil bypass springs on Gen VI 502
 

I was getting low oil pressure (<10 psi) at idle, immediately after a hard run. After fast idling for a few minutes the pressure would come back to 25 psi at idle. Cold starting pressure and WOT pressure were fine. When I changed the oil it was BLACK!

When I talked to my engine builder he said they had the same problem on another 502 (in a truck) and the owner of that engine had found out from Scoggin-Dickey (a GM Performance Parts dealer) that it might be the oil bypass springs in the oil filter pad on the block. If they were opening at WOT then the oil wasn't getting filtered or cooled. All Gen VI engines come off the assembly line with 11 psi springs installed.

I figured that in the marine situation the extra back pressure of lines, fittings and oil cooler could cause this bypass valve to open as though there were a plugged filter on the filter pad. Hot oil and no viscosity would be the result, then low oil pressure. The temperature sender in the side of the block was not picking up high temperatures but since they have never shown more than 180F I wasn't sure if I could trust them.

I had to remove the engines to look, but sure enough there was an 11 psi spring where there should have been a 30 psi spring (PN25161284). This spring is installed in the outer hole of the filter pad.

I also removed the bypass spring that was installed in the center hole. All this bypass does is divert oil to the oil cooler holes in the block. It only opens if an oil cooler (plumbed to these holes in the block) is plugged. Since my oil cooler is plumbed in line with the remote oil filter, as Mercury does it, these holes are not used and removing the bypass valve and spring allows the oil returning from the remote line to enter the main oil passage without taking three redundant 90 degree turns.

I also noticed that for some reason the oil line leaving the block and going to the remote filter had three 90 degree brass fittings and a short section of hose. I had never questioned this before but now I was "educated" and saw these as redundant. I replaced them with straight fittings and a long sweeping bend in a longer hose.

So what was the result of these changes? I have 35 psi at idle immediately after a hard run. Problem solved I think.

When I bought these engines as rebuildable cores I was told that they were warranty returns to one of the smaller engine marinizers. Guess what the problem was? Yep, wiped out bearings due to lack of lubrication.Something to think about when you are doing your oil lines/system.

For more information contact Scoggin-Dickey Parts Center at 1 (800) 456-0211 and ask for their Tech Sheet on BBC Gen VI Oil Systems.

Thanks for the tip!

Any idea Tomcat if the mark IV 454s have the same situation? I get similar results to your before changes made scenario.

Dave

I believe this is only a genVl block problem.

TC- I am guessing the oil was not going thru your filter also.

Gen VI problem
 

I have a Gen VI and a common problem that is all ways overlooked is in the lifter alley there are 3 1/8" NPT plugs that need to be plugged, if not that will cause lower oil pressure.

When you have your block at the machine shop they usually remove all those nice little plugs, unless you have them replug them or do it yourself, they are usually overlooked.

I also plug the cooler holes in the block and run an oil pad to a remote filter then cooler.

Just a thought.

Thanks Turbo.

BT :cool:

Tomcat, You are correct. I did the exact same things as you did when I installed my rebuilt Gen V 502 last year. :cool:

Ditto. I have 3 Gen VI 502s and I've replaced the oil bypasses on all of them. It's amazing that a $3 part can cause such pain....

I just changed mine a week ago. I could only find one on the filter pad the center return had nothing in it. The engines use the Merc remote set up so I am not sure how this change effected my oil system. What I do seem to have is lower than I would like to see oil pressure on that side (especialy after a run) and the oil seems to darken fast. I also changed to a Mellings HV pump. Any ideas or thoughts?

I have a similar problem on mine, but how do I know what I have? Gen VI or Gen V
It is a 97MPI without the fuel pump mount, but it has v belts. So How can I look at it and tell which it is, so I know if I should dig into the oil spring. Do you just buy the spring from any GM dealer?