Oil pump pressure relief valve?
09-23-2013, 10:05 AM
#1
Oil pump pressure relief valve?
I finally got my boat out for a test run this past weekend. I noticed some weird behavior involving my oil pressure. History:
I have a stock gen vi 454 425 ho crate motor with 10 hrs on it. I ran it on a stand last year and it had 50 or so lbs of oil pressure at idle. In the boat idling around the dock after the first startup last week it had 50 lbs at idle. This past weekend I took it out and on plane roughly 3000 - 3800 rpms it had over 70 lbs. For short spurts I may have had the rpms as high as 4000 and at that time the oil pressure went over 80 lbs close to 90. As the oil temp heated up (between 190 - 200 degrees) I noticed the oil pressure came down to something closer to 60 lbs. This seemed fine. When I backed it down and idled for a bit the pressure went down close to 0 lbs. I shut it down, checked what I could in the boat, but no issues. The engine water temp was around 175 and oil temp was around 190, but cooled off on idle. When I started it back up, the oil pressure was close to 0 lbs. Running along up on plane after that to get it home at about 2500 rpms or so, the oil pressure was notchy between 30 and 40. It would jump in 5 to 10 lbs increments back and forth. Not smoothly on the needle. But the boat ran fine on this run back.... a little more rpms and the pressure was between 40 and 50 lbs steady. As soon as I get off plane and idle it would be close to zero. The pressure alarm just barely touched off twice in in 2 sub second little bursts. So I don't think it is the gauge since they have separate senders. If I put it in neutral and blipped the throttle real quick the pressure would go up to 15 lbs and stay there while idling. The motor sounded good and felt good in the boat. I didn't really have the conditions to get it up over 4000 rpms and I didn't want to after the oil behavior issues.
Does this seem like it could be the oil pump pressure relief valve? I have a 30 lb filter bypass in it and the center bypass valve removed. This is basically a 454 stock setup. All merc externals bolted to the block, circ pump, oil/power steering cooler. It has holley 750 dp and gil dry exhaust.
I have a stock gen vi 454 425 ho crate motor with 10 hrs on it. I ran it on a stand last year and it had 50 or so lbs of oil pressure at idle. In the boat idling around the dock after the first startup last week it had 50 lbs at idle. This past weekend I took it out and on plane roughly 3000 - 3800 rpms it had over 70 lbs. For short spurts I may have had the rpms as high as 4000 and at that time the oil pressure went over 80 lbs close to 90. As the oil temp heated up (between 190 - 200 degrees) I noticed the oil pressure came down to something closer to 60 lbs. This seemed fine. When I backed it down and idled for a bit the pressure went down close to 0 lbs. I shut it down, checked what I could in the boat, but no issues. The engine water temp was around 175 and oil temp was around 190, but cooled off on idle. When I started it back up, the oil pressure was close to 0 lbs. Running along up on plane after that to get it home at about 2500 rpms or so, the oil pressure was notchy between 30 and 40. It would jump in 5 to 10 lbs increments back and forth. Not smoothly on the needle. But the boat ran fine on this run back.... a little more rpms and the pressure was between 40 and 50 lbs steady. As soon as I get off plane and idle it would be close to zero. The pressure alarm just barely touched off twice in in 2 sub second little bursts. So I don't think it is the gauge since they have separate senders. If I put it in neutral and blipped the throttle real quick the pressure would go up to 15 lbs and stay there while idling. The motor sounded good and felt good in the boat. I didn't really have the conditions to get it up over 4000 rpms and I didn't want to after the oil behavior issues.
Does this seem like it could be the oil pump pressure relief valve? I have a 30 lb filter bypass in it and the center bypass valve removed. This is basically a 454 stock setup. All merc externals bolted to the block, circ pump, oil/power steering cooler. It has holley 750 dp and gil dry exhaust.
09-23-2013, 06:21 PM
#5
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Sounds to me like your oil is getting hot and losing viscosity. When you say you are using all the stock Merc stuff, including the power steering-engine oil cooler, it sounds exactly like what happened when I replaced my 454 with a 502 and initially used all the stock stuff, too. Your stock components were never meant to handle the heat that a 425 hp motor produces. I ended up plumbing in a separate 12 x3 " oil cooler and a separate ps cooler. Now the oil temp stays down and the oil pressure stays up at idle after a run. Check your oil temp at the filter with an infrared temp reader. I bet your gauge is off by quite a bit. Good luck.
09-23-2013, 06:35 PM
#6
Macdad, This motor is basically the 454 mag setup. I think the 365 hp 454 mag is the same motor basically. I built up a 454 mag efi with a new cam, head work, lifters, rockers, ecm, etc and the oil system seemed to handle that fine. I really don't think the oil temp was getting too hot. I also had the motor shut down for an hour or so and when I restarted it at idle I still had the problem.
09-23-2013, 06:39 PM
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Oil temps don't seem bad at all but at WOT that's what I get, you are not WOT is the part that concerns me, cruising I never see more then 160, I also run no stats as I like things cool, last longer....
I would put mechanical gauge, but first cut oil filter open, you said you had 50 PSI before? that's not enough depending on clearances, I been there before, everyone said I was fine with 50 psi, wiped out mains 4 times that summer from hell, soon as I listened to my buddy and got HV pumps we shimmed them for 80 PSI, not once have I had an issue since, I also run the 30lb bypasses things stay good all around, I would cut oil filter open before you turn the key again, if all looks good there its a sender or just plain ol not enough pressure, if clearances are .030 or bigger as they should be, you need HV high pressure..trust me....
I would put mechanical gauge, but first cut oil filter open, you said you had 50 PSI before? that's not enough depending on clearances, I been there before, everyone said I was fine with 50 psi, wiped out mains 4 times that summer from hell, soon as I listened to my buddy and got HV pumps we shimmed them for 80 PSI, not once have I had an issue since, I also run the 30lb bypasses things stay good all around, I would cut oil filter open before you turn the key again, if all looks good there its a sender or just plain ol not enough pressure, if clearances are .030 or bigger as they should be, you need HV high pressure..trust me....
09-23-2013, 08:17 PM
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Was the motor a new stock crate motor? If it is maybe you have a warranty claim. BTW, my oil pressure was never erratic, it just dropped real low at idle after a run. It always came back with a little throttle. Hope it ends well.
Last edited by MACDAD260; 09-23-2013 at 08:21 PM.
09-23-2013, 08:20 PM
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I don't think you meant .030 clearance. I have a customers cruiser with a 454 crusader doing the same thing. Gonna try 2 things, different brand of oil, then drop the pan and put a new pump in, hoping to find the relief valve sticking. We just put a long block in last year
