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Thread: Strange Oil Pressure Problem

  1. #1
    gqchris
    HEy Guys,
    I Posted this over in the blower motor forum but I dont think that too many peeps head over there. I was hoping for some help with the jet guys.
    Last season I acquired a 1976 Southwind 18.5' with a built 468 with a jet. Please forgive me if I mess any of the terms up here (novice), but I believe it has a BDS 671 Blower, the guy I bought it from said it was tuned at 6lbs boost. Supposedly a Merlin block.
    Anyways, took it out for its test run last year at Elsinore, and I noticed that the oil pressure gauge was not reading at all. (Stuck at 60lbs). So i replaced the oil sending unit on the block and tried it again. This time it was reading between 50-60 lbs and fluctuated with the blower surge. I figured this was normal and took it for a hot lap around the speed zone. Everything was fine, turned the corner at the end to come back, ran great and then i noticed the oil pressure falling. By the time I got back to the no wake zone, I was down to 15 lbs or so and I turned it off. I rowed back in in fear of causing permanent damage. Got to the dock, started it back up, same pressure, immediately shut it off. Nothing sounded strange during this, no knock, no chatter, no rocker noise. No elevated Temp. Let it set for 30 mins, pressure back up when started
    I figured maybe a cause was that when I changed the oil before I ran it, I had put 30w instead of 50w. Put 50w back in, same thing happened next time at Elsinore. Ok, so I figure the gauge in dash is funky. Bought a mechanical Mac gauge to plug right into the oil galley hole and hold while i was driving. SAME THING!
    So this is what a few peeople have suggested. Bad Lower Bearing, Oil Sender Hole wrong size, Blower scavenging the oil??? Any help would be greatly appreciated to point me in the right direction to pull it out and rebuild it or throw in the towel Thanks for the help guys!

  2. #2
    Cas
    what's the temp of the oil after a hard run?
    If it's getting too hot, it will cause lower pressure readings.
    is there enough oil? maybe too much?
    If there's too much oil, the crank will cause the oil to foam up which causes the pressure to go down.
    If there's not enough, the oil may not be returning to the pan fast enough.
    The other thing is, doies it have the right pick-up installed for the pan? Could also be the pick-up screen fell off.

  3. #3
    1978 Rogers
    I have the same problem. I always put to much oil in mine and my pressure drops down to 40-50 in stead of high 60. Drain a little out. Take it back to the lake and just run it for an hour or so, not hard. This should wip it up and put bubble the oil. Pull the dip stick and see if you have bubbles. If not run it a little harder and re check the oil. I try not to make really sharp corners. It really sloshes the oil and you pressure will really drop.

  4. #4
    gqchris
    what's the temp of the oil after a hard run?
    If it's getting too hot, it will cause lower pressure readings.
    is there enough oil? maybe too much?
    If there's too much oil, the crank will cause the oil to foam up which causes the pressure to go down.
    If there's not enough, the oil may not be returning to the pan fast enough.
    The other thing is, doies it have the right pick-up installed for the pan? Could also be the pick-up screen fell off.
    Hey Steve,
    The oil temp seems fine, I have a gauge that I think is accurate, and it reads normal levels. I have double checked the oil 10 times over, the only thing I can think of is maybe the stick is wrong? It is a hand marked custom job by the previous guy, but it is dead on the money when i add the quarts after a change, the pan is 10 qt i believe, or 12. I forget without looking at it.

  5. #5
    gqchris
    I have the same problem. I always put to much oil in mine and my pressure drops down to 40-50 in stead of high 60. Drain a little out. Take it back to the lake and just run it for an hour or so, not hard. This should wip it up and put bubble the oil. Pull the dip stick and see if you have bubbles. If not run it a little harder and re check the oil. I try not to make really sharp corners. It really sloshes the oil and you pressure will really drop.
    I would be in love with 40-50 lbs!! 10-15 lbs is what is scaring me! I will check for bubbles next run though

  6. #6
    Wet Dream
    I'm just running my little Olds 461, but I was going through the same worries. I've learned to live with it for the second season, and its still holding up great. Through SEVERAL sources, I was told to run the mains and rods with loose tolerances (.030 mains, .033 rods) to keep the oil flowing in the bottom end. On inital startup, with 50wt, i would 50psi at cold idle. As it warmed up, the clearances would open up leaving me at...get this...22psi at 3000rpm and up, and 9 to 12 psi at hot idle. I would not get ANY lifter noise, nothing rattling and not any strange noise at all. Scared the shit out of me the first few times, but it seems to be holding up quite well and the oil isn't breaking down as quickly as it would with higher pressures. I would have to change the oil after every other weekend with the tighter clearances. Now its every 4 times or so. This loose setup seems to keep the longevity in the oil. And when it would cool down, I would fire it up and its right back at 50psi cold. It really does scare, but I'm getting used to it.

  7. #7
    76elimspecial
    HEy Guys,
    I Posted this over in the blower motor forum but I dont think that too many peeps head over there. I was hoping for some help with the jet guys.
    Last season I acquired a 1976 Southwind 18.5' with a built 468 with a jet. Please forgive me if I mess any of the terms up here (novice), but I believe it has a BDS 671 Blower, the guy I bought it from said it was tuned at 6lbs boost. Supposedly a Merlin block.
    Anyways, took it out for its test run last year at Elsinore, and I noticed that the oil pressure gauge was not reading at all. (Stuck at 60lbs). So i replaced the oil sending unit on the block and tried it again. This time it was reading between 50-60 lbs and fluctuated with the blower surge. I figured this was normal and took it for a hot lap around the speed zone. Everything was fine, turned the corner at the end to come back, ran great and then i noticed the oil pressure falling. By the time I got back to the no wake zone, I was down to 15 lbs or so and I turned it off. I rowed back in in fear of causing permanent damage. Got to the dock, started it back up, same pressure, immediately shut it off. Nothing sounded strange during this, no knock, no chatter, no rocker noise. No elevated Temp. Let it set for 30 mins, pressure back up when started
    I figured maybe a cause was that when I changed the oil before I ran it, I had put 30w instead of 50w. Put 50w back in, same thing happened next time at Elsinore. Ok, so I figure the gauge in dash is funky. Bought a mechanical Mac gauge to plug right into the oil galley hole and hold while i was driving. SAME THING!
    So this is what a few peeople have suggested. Bad Lower Bearing, Oil Sender Hole wrong size, Blower scavenging the oil??? Any help would be greatly appreciated to point me in the right direction to pull it out and rebuild it or throw in the towel Thanks for the help guys!HAD THE SAME PROBLEM WITH MY STOCK 460. CHECKED EVERYTHING AND CAME UP WITH NOTHING. ONCE IT HEATED UP THE OIL PRESSURE DROPPED TO 15PSI, BUT STILL RUNNING STRONG. THREW ON A WIX FILTER AND REPLACED 1QT. OF OIL WITH A QT. OF LUCAS AND IT BROUGHT ME BACK UP TO BETWEEN 45-50 .

  8. #8
    gqchris
    I'm just running my little Olds 461, but I was going through the same worries. I've learned to live with it for the second season, and its still holding up great. Through SEVERAL sources, I was told to run the mains and rods with loose tolerances (.030 mains, .033 rods) to keep the oil flowing in the bottom end. On inital startup, with 50wt, i would 50psi at cold idle. As it warmed up, the clearances would open up leaving me at...get this...22psi at 3000rpm and up, and 9 to 12 psi at hot idle. I would not get ANY lifter noise, nothing rattling and not any strange noise at all. Scared the shit out of me the first few times, but it seems to be holding up quite well and the oil isn't breaking down as quickly as it would with higher pressures. I would have to change the oil after every other weekend with the tighter clearances. Now its every 4 times or so. This loose setup seems to keep the longevity in the oil. And when it would cool down, I would fire it up and its right back at 50psi cold. It really does scare, but I'm getting used to it.
    You guys have me thinking now that maybe this is normal and I should just run it I am at the point now that any fun out of it would be better than nothing!

  9. #9
    CrdStang
    While a drop in oil pressure isn't good, if you still have 10psi per 1000RPM, your engine is fine. In fact, that's an old standard and you can deffinately get away with less because oil is a bunch better than it was 20 years ago.
    My general rule is, if A: the oil pressure is reasonably stable (not like the pan is getting sucked dry or something, no sudden drops), and B: Your engine isn't making any scary noises, then you are probably OK.
    I'd say it's oil temp causing your pressure loss BTW.

  10. #10
    Wet Dream
    Run it. I'm not going to tear mine down to find out that nothing is wrong with it.

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