mackrmodel686st Posted June 11 Share Posted June 11 I've got a strange problem with a 2001 vision with the v-mac iii e7-427. The oil pressure drops to under 5 psi at idle if I drive it a few miles. If I shut the truck off and immediately start it back up the oil pressure at idle is about 20 psi. It will stay around 20 psi at idle till I drive it again. Thought maybe the gauge in the dash or the sender was going bad, so we put in a mechanical gauge with a plastic oil line to the filter housing. Both gauges do the same thing. Truck will have about 40 psi going down the road, but drops to under 10 while driving and under 5 at idle. Does anyone have any ideas what is going on? Thanks. Quote Link to comment Share on other sites More sharing options...
fernando_say Posted June 11 Share Posted June 11 Pick up tube clogged or filters clogged? Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 11 Share Posted June 11 More likely a sticking pressure relief in the oil pump. It doesn't seat all the way once running at speed opens it a bit. Another but less likely is a crack or air leak in the suction line to the pump. Either way, I think the oil pump is worth a close look at. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted June 11 Share Posted June 11 I have seen the welch plugs in the end of the rocker shafts move, or just pop out. The condition you have is similar to that issue.. pull the valve covers and take a peak.. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 12 Share Posted June 12 I would expect a rag or something like that in the pan, to be drawn against the pick-up as soon as the engine speed is increased, not allow 40 psi then drop to 5 at idle, but I could be wrong, and worth a look. 1 Quote Link to comment Share on other sites More sharing options...
Popular Post Joey Mack Posted June 12 Popular Post Share Posted June 12 it's a possibility.. however, this oil pump in my opinion is excellent. and no other failures or issues were stated.. Of course I am diagnosing from my couch, but this engine has been known to push the welch plugs out of the rocker shafts, and you will see oil pressure, but of course not enough to lube the engine properly.. I would like to know what repairs were done recently.. For some reason my 'knee jerk reaction' is the welch plugs.. I am familiar with being wrong,,, I'm Married 2 1 Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 12 Share Posted June 12 Oh, I make no claim to be correct, only places I would look. Your experience on the engine is far greater than mine. I am just trying to fix the symptoms to something that would match up. I did have one engine where the relief would stick, and needed to kick it further open to free it, and that is something that can't happen with hot oil. I very well may be way off base. 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted June 12 Share Posted June 12 Your good. I just toss some humor in the mix.. you are brilliant.. 1 Quote Link to comment Share on other sites More sharing options...
mackrmodel686st Posted June 12 Author Share Posted June 12 9 hours ago, fernando_say said: Pick up tube clogged or filters clogged? New filters and new pump. Quote Link to comment Share on other sites More sharing options...
mackrmodel686st Posted June 12 Author Share Posted June 12 7 hours ago, Geoff Weeks said: More likely a sticking pressure relief in the oil pump. It doesn't seat all the way once running at speed opens it a bit. Another but less likely is a crack or air leak in the suction line to the pump. Either way, I think the oil pump is worth a close look at. The pump is brand new. Quote Link to comment Share on other sites More sharing options...
mackrmodel686st Posted June 12 Author Share Posted June 12 7 hours ago, Joey Mack said: I have seen the welch plugs in the end of the rocker shafts move, or just pop out. The condition you have is similar to that issue.. pull the valve covers and take a peak.. The plugs in the rocker shafts are threaded in to the shafts. I've seen what you are talking about, but I think mack did an update to the shafts sometime between 1999 and 2001. Quote Link to comment Share on other sites More sharing options...
mackrmodel686st Posted June 12 Author Share Posted June 12 7 hours ago, Geoff Weeks said: I would expect a rag or something like that in the pan, to be drawn against the pick-up as soon as the engine speed is increased, not allow 40 psi then drop to 5 at idle, but I could be wrong, and worth a look. I would suppose a rag is possible, the pan was off to replace the pump. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted June 12 Share Posted June 12 I read this again. New oil pump, 2001 with the large nuts on the end of the rocker shafts ?? Seems odd, but ok. Hand held gauge shows the same low pressures,, how many hours on the engine? Have you rolled a set of rod and main bearings recently? I have seen that boost pressure 15 PSI. Sounds like you have a good knowledge of this engine.. Jojo Quote Link to comment Share on other sites More sharing options...
fjh Posted June 12 Share Posted June 12 Fuel dilution is a possibility! Oil level??? 1 Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 12 Share Posted June 12 4 hours ago, mackrmodel686st said: The pump is brand new. Unfortunately that doesn't mean it can be crossed off the list of things. I had one on a Big Cam 4 where the primary relief (the Big cam has two, DFC has another relief that senses pressure at the end of the rifle bore) wasn't drilled all the way thru, on cold start it would peg the pressure beyond 100 psi. warm it would act normal. Somehow that oil pump made it through the system on on to an engine, and out the door. My thinking is the relief expands just enough to not fully seat when the RPM drops with hot oil, when the oil stops moving and all pressure is gone, it seats so pressure is restored until the rpm rises enough for the relief to need to open a bit, then the cycle starts again. I had one engine where the relief would stick every once and a while, but that engine the oil pump was external to the pan and you could pull the relief without too much pain. Not saying this is 100% what the problem is, only a possibility that fits the symptoms fairly well. A rag does also but I would expect it to be quicker acting. Some engines also use a bypass oil valve that only send excess oil through the bypass oil filter when the system is over a set pressure (often around30-35 psi) and if this is stuck open or a weak spring it may pass oil through the bypass oil filter when there isn't enough volume to keep the oil pressure up. I don't know about the engine you have, these are just general thoughts that can apply to all large diesels, some of it may not apply to the Mack engine you have. 1 Quote Link to comment Share on other sites More sharing options...
67RModel Posted June 12 Share Posted June 12 6 hours ago, mackrmodel686st said: The pump is brand new. Why is the pump brand new? Was it to try and correct this problem you are having? Meaning, did the engine have the exact same symptoms before the oil pump was replaced? When did the symptoms start? 2 Quote Link to comment Share on other sites More sharing options...
mackrmodel686st Posted June 20 Author Share Posted June 20 On 6/12/2024 at 8:23 AM, 67RModel said: Why is the pump brand new? Was it to try and correct this problem you are having? Meaning, did the engine have the exact same symptoms before the oil pump was replaced? When did the symptoms start? That truck had rods and mains done years ago and the jake stopped working immediately after. Oil pressure always seemed on the low side as well but was within tolerance. We were replacing heads and gaskets and decided to try and fix the jakes at the same time. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted June 21 Share Posted June 21 Im a bit stumped. I think there is a welch plug inside the centrimax filter housing. Has it popped out? Its under the filter.. Quote Link to comment Share on other sites More sharing options...
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