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4.0 Oil Pressure Help


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Well I just bought my first comanche and it has some problems that I didn't see when I look at it. My question how much oil pressure should I have at idle. I had 40psi when it starte it but after driving it dropped to zero but never knock hammered ticked or anything. So today I put in a mechanical gauge and changed the oil fire it up and have above 40psi drove it around and it dropped to around 6-7 but never hammered or knocked. I am thinking of putting a pump in it but thought I would ask for some advise or if I was missing something. Thanks Brandon

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The factory spec for oil pressure is 13 psi minimum at idle, 37 to 75 psi above 1600 RPM. (At normal operating temperature.)

 

How many miles on your engine? It's more likely that you need rod bearings rather than an oil pump. Since you have to drop the pan to change either, I'd say do both while it's open.

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I would expect you won't like the looks of the inside of the valve cover ... and can likely expect some new noises as the clean oil disolves some of the deposits. I got a similar surprise in my 4.0L ... although it does maintain 40psi over 1500rpm and about 20 at idle now. It bounced around a bit when I got it. The valve cover was a nightmare, and the oil filter was seized to the adapter. I now have a tapping noise at idle but nothing at speed amd plenty of power so I'm hoping its a manifold leak. Wrong pitch for lifters, too high and inconsistent to be rods. Going to swap the pump and rod bearings anyway.

 

If its running strong without noises ... is it at all possible there are deposits blocking the pressure port but not the main galleries? I would expect an engine with little to no oil pressure to make some nasty noises. I know my 2.5L did when the pressure sensor in my old YJ blew up, emptying the crank case on the way home one night. Not something I care to hear again.

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  • 2 weeks later...

Hey all it's been a long time and I just had the same problem. I just put new gauges awhile back and the oil pressured dropped to zero and I just recently put in a new oil and filter (Valvoline and Fram) ??? and after some troubleshooting elimination the gauge, sensor I then removed the oil filter and there was no oil in the filter even though the oil pan was full. I then decide to change the oil and filter again with Pennzoil 10W-30W and new WIX oil filter (No it wasn't the filter) this time as a last resort before I drop the pan. I then remove the distributor and primed the oil pump took awhile until I saw the oil coming out at oil filter housing. Oil pressure is over 40psi at Idle just like it was before, my question is why didn't the oil pump, pump when the engine was running with no oil flowing even though it was a making contact was it air bubbles, cheap oil or is the oil pump going bad? Truck only has 86K original miles.

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Hey all it's been a long time and I just had the same problem. I just put new gauges awhile back and the oil pressured dropped to zero and I just recently put in a new oil and filter (Valvoline and Fram) ??? and after some troubleshooting elimination the gauge, sensor I then removed the oil filter and there was no oil in the filter even though the oil pan was full. I then decide to change the oil and filter again with Pennzoil 10W-30W and new WIX oil filter (No it wasn't the filter) this time as a last resort before I drop the pan. I then remove the distributor and primed the oil pump took awhile until I saw the oil coming out at oil filter housing. Oil pressure is over 40psi at Idle just like it was before, my question is why didn't the oil pump, pump when the engine was running with no oil flowing even though it was a making contact was it air bubbles, cheap oil or is the oil pump going bad? Truck only has 86K original miles.

http://www.orangetractortalks.com/forums/showthread.php?t=11672&highlight=no-flow+filter

 

No-flow filters are a SERIOUS problem.

 

Above is my thread from elsewhere.

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I don't think that was my problem after the oil and filter changed it was working ok then one day it just showed no oil pressure. I believe the oil pump was spinning but no oil was flowing through the block as the lifters were rattling a lot due to no oil flow. I then placed the new oil filter on and started it with the old oil and nothing no pressure then I changed out the oil and primed it with drill all is good now...

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