Oil pressure relief valve?

My jeep ('92 xj) has 253k on her and the oil pressure jumps up to normal, and after warmup, pegs out past 80. I am pretty sure it is a stuck valve, like the oil pressure relief valve. I would like to know if simply pulling the oil pump, and cleaning the crap out of it would possibly fix the problem, or if i need to replace something. Hell, she runs fine, but i don't know how long I can run with high pressure without complications (if this will cause any). This is the 4.0 HO engine, and it was rebuilt around 150k by some old guy who knows less about engines than I do. I have fixed tons of crap he left loose or didn't propperly install. Any and all coments appreciated. And yes, I have read through tons of threads and searched this forum for awnsers... but no awnsers apply to my specific problem.

Your problem could simply be a faulty oil pressure gauge sending unit. They're known to fail and cause the problem you describe. Replace it and see if that makes any difference. You could also verify the oil pressures with a mechanical gauge.

Logic tells me that cold oil is thicker than thin oil, so the chances of it getting warm then pegging/sticking the valve is probably less as it gets warm. It sounds like the sending unit may be getting warm and malfunctioning.
As far as my research has taken me is, that in all probability the cam is the first thing that gets oiled, there is a riser (oil up passage) that goes up a short distance from the filter base, then goes front and rear to oil the cam, then on to oil the crank from outlets on the front to rear passage.
There is a pressure relief valve/bypass in the oil filter and also in the pump itself. And then the short riser before the oil spreads out.
First thing I'd do is hook up a mechanical gauge and/or swap out the sending unit. If a mechanical gage shows high pressure, fairly immediate action is necessary. Starving the cam/crank of oil can cause all sorts of serious greif.
I picked up a cheap low pressure refrigeration gauge (works just fine for everything from fuel to oil, freon is a fairly aggresive solvent) a yard of fine copper tubing (fittings already attached and with a built in tit to compress a tire valve) and a fitting with the proper connections that screws right into the same outlet as the sending unit for like $20 (fairly common refrigeration pieces). I've had it forever and have used it on various motors with the same fitting and a couple of others when neccesary.

The only reason I think it is a valve is because I have seen valves in Ford engines with high miles stick when they are supposed to open when the thermostat kicks in. But I also saw the oil filters after a few miles in those engines and it crushed the internals in them, this is not the case in my jeep. I honestly know little of the inner workings of the oil system in a 4.0L engine, since I have never had to work on one (beyond replacing the pump and a few dented pans) Everything in the engine that seems to be getting lubrication. But I will go get a guage and a new sensor first thing in the morning and switch it out, the old one is in great shape physically, and so is the connection. I'll post again tomarrow and let you know how it pans out.

D3ATH_F3YD said:

The only reason I think it is a valve is because I have seen valves in Ford engines with high miles stick when they are supposed to open when the thermostat kicks in. But I also saw the oil filters after a few miles in those engines and it crushed the internals in them, this is not the case in my jeep. I honestly know little of the inner workings of the oil system in a 4.0L engine, since I have never had to work on one (beyond replacing the pump and a few dented pans) Everything in the engine that seems to be getting lubrication. But I will go get a guage and a new sensor first thing in the morning and switch it out, the old one is in great shape physically, and so is the connection. I'll post again tomarrow and let you know how it pans out.

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Just remember, don't use any teflon tape on the sender, the threading is part of the circuit. The pump in jeep is what I've come to know as an IMO pump [I Move Oil] just a gear set that moves oil as it turns, these pumps are capable of great pressure, the filter is more or less what acts as the regulator, when it plugs and reaches a certain pressure a bypass valve kicks in and bypasses the filter. They tend to fail and either leak or short/open, they also can get damaged by getting whacked a few times changing the filter or working in that are, plastic body on the sender.