I'm having a problem with the oil pressure on a recently rebuilt late model Atomic 4 engine, about 3 hours since the rebuild by a very experienced mechanic. I'm using SAE 30W oil and the oil pressure gauge, oil pressure sender, and wiring are all new. The pressure starts out high at 75PSI cold, but over time the pressure gradually falls to 11PSI after 1 hour at 1600RPM (this is where I ended my test).
I've read that problems with the oil pressure relief valve can cause symptoms like:
- a decrease in oil pressure when adjusting the valve to increase oil pressure
- oil pressure decreasing as RPM increases
but this doesn't sound like the problem I'm having.
I'm going to try to find a mechanical pressure gauge to verify the readings, but I'm not too hopeful that this is just a faulty gauge because of the pattern of the readings.
I saw a part in the catalog that says:
"When the output from an oil pump drops off below a certain point, oil pressure will decay over several hours of operation even though all bearing clearances are normal. When this condition occurs, the problem is seldom excessive wear on the oil pump gears themselves, but wear within the housing of the rear main bearing cap in which the gears rotate (including the four holes in the housing which serve as bearings for the rotating shafts of the gears)."
This sounds like it could be the problem I'm having; is this something that is likely to be missed in a rebuild? Is there anything else I should consider? Could this be due to a faulty spring in the oil pressure regulator?
I've attached the pressure, temperature, and RPM data from a 1 hour test run where it started in neutral for 10 min, then shifted to forward and I increased the throttle a bit at 15min.
I've read that problems with the oil pressure relief valve can cause symptoms like:
- a decrease in oil pressure when adjusting the valve to increase oil pressure
- oil pressure decreasing as RPM increases
but this doesn't sound like the problem I'm having.
I'm going to try to find a mechanical pressure gauge to verify the readings, but I'm not too hopeful that this is just a faulty gauge because of the pattern of the readings.
I saw a part in the catalog that says:
"When the output from an oil pump drops off below a certain point, oil pressure will decay over several hours of operation even though all bearing clearances are normal. When this condition occurs, the problem is seldom excessive wear on the oil pump gears themselves, but wear within the housing of the rear main bearing cap in which the gears rotate (including the four holes in the housing which serve as bearings for the rotating shafts of the gears)."
This sounds like it could be the problem I'm having; is this something that is likely to be missed in a rebuild? Is there anything else I should consider? Could this be due to a faulty spring in the oil pressure regulator?
I've attached the pressure, temperature, and RPM data from a 1 hour test run where it started in neutral for 10 min, then shifted to forward and I increased the throttle a bit at 15min.
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