oil pressure

[MadDog]

At cold start the oil pressure goes up to 20, then after it warms up the oil pressure drops to 0. I have changed the timing cover, main bearings, oil pump gears, rod bearings, lifter and push rods. I had the engine rebuilt last year, the people put the wrong pistons in and they were coming apart.So I had to replace everything that I have listed. Any ideas would be greatly appreciate.

You can e-mail me at DougEMacLeod@msn.com or my wife at AngelaLMacLeod@msn.com. I am very seldom on the computer.

[The Anti-Chrysler]

What vehicle and what engine???? 360 (from the timing cover remark)???

[MadDog]

1977 Jeep Wagoneer, with a 401.

[JeepFreak]

Are you gauging the pressure from the stock gauge? I have put an aftermarket gauge on in the past with one reading zero and had the stocker be off by as much as 20.

[joe]

Worn cam bearings will cause low oil pressure also but those should be new enough if it was rebuilt a year ago. As Jeepfreak mentioned these stock gauges aren't very good. I would plug in a mechanical gauge first to see if your really do have low pressure. When you did the oil pump gears did you check the side and end clearance of the gears. Also the replacement gasket that comes with the gears is a tolerance gasket and must be used rather than making one of an unknown thickness.

[The Anti-Chrysler]

It is common for the oil pressure to drop in the RANGE that you mentioned from cold to hot, so 20 psi isn't too bad. However it should be from like 45 PSI to maybe 20-25 PSI hot. Start where like the others said and make sure your gauge is accurate. The oil sensor assemblies often get cooked with old, thick greasy oil, and they get inaccurate. Or, there could be a loose connection in the wiring. Start there to see if the engine really has a problem.

If the oil pressure was really 0, then the engine would almost surely knock, tick, or lock up.

[MadDog]

I have put a mechanical gauge on it and it reads the same. There is very little oil getting to the rockers. You can run it with the valve covers off with out any bad oil splashing out. I have taken the sender unit out to make sure it was flowing and it was. The gears and the housing are new and the gasket that comes with the gears was used.

[Jeeptruck]

Sounds like clogged oil passages, try some cleaner or what is sometimes called top engine cleaner (mainly used to free stuck valves)

[wagontrain]

Was your oil pump screen thoroughly cleaned out when the engine was rebuilt? I've never torn into an AMC engine, but in other engines the screens tend to accumulate all sorts of debris (mostly pieces of valve stem seals) over the years. I had the same problem on an old truck a few years ago, and cleaning out the screen solved it.

[MadDog]

I have tried engine cleaner, but it didn't do any good. The oil pump screen was thoroughly cleaned out.

[FYR WOOD]

I had similar problems on my 4.0L XJ. And when it lost oil pressure the engine actually sounded like a diesel. I changed the oil filter, put in 3 quarts of 10W-40 and 2 quarts of kerosene and ran the engine for about 30 minutes at idle, basically using the kerosene to flush the pump screen. Drained the oil, and changed the filter again, put in new 10W-40 oil and I am consistently getting about 30-40 pounds of oil pressure, and no valve noise. Just my $.02...

Scott

[MadDog]

I have changed the oil filter and the type of oil I was using, but didn't make a difference.

[bvibert]

Did you check the bearing clearances when you put the new ones in? Did you replace the spring and plunger in the oil pump when you did the gears? Maybe the plunger is getting stuck open and not allowing pressure to build? I know you said you put a new timing cover on, but did you check the side and end clearances of the gears with the new cover? I've heard of brand new covers being out of spec.

[fredws]

Correct me if I am wrong, but wouldn't plugged passages increase the oil pressure?

I have to agree with bvibert, sounds like the plunger stuck open, or clearances out of spec. Have a look at the plunger, since it would be the easiest to get at.

[Crazy_Jeepman]

Originally posted by fredws:
[QB]Correct me if I am wrong, but wouldn't plugged passages increase the oil pressure?
QB]No it won't, as the pressure bypass will not allow it to go over the PSI it is set for. Unless it is not free to move. I doubt it has a plugged oil passage, not something that would happen as a rule, and if it does engine failure is very very sudden. Bottom line is you have very poor oil pressure, causes for this is as mentioned, poor pump condition, bad cam bearings, bad mains or rods, maybe the cam bearings weren't changed when the engine was rebuilt, badly by the sounds of it. Good Luck ;)

[fredws]

I guess I should have said "partially" plugged. But anyway, I agree I think it is something with the pump, or bearings.

[wordsmith]

May or may not help: I have found that STP Engine Flush does an incredible cleaning job [freed up several badly stuck lifters on a Ford 302] better than 'fast flushes' that are merely kerosene. It can be hard to find and costs about $8 a bottle, but you can run it for 20 minutes for thorough cleaning.

If you fear there isn't enough lubing, switch to a full synthetic oil: do a STP flush, use a new 'ultra' grade filter, then fill with a synthetic like Castrol or a reputable brand; let it idle for a while and keep an eye on it for unusual sounds or vibes.

They claim to have run engines w/o oil after they had been run a while with Castrol, so maybe the synth can coat the parts enough to prevent seizure. Motor-Up claims the same thing but is expensive and can't be better than plain old synth oil [never tried that but I use synth in all but the oldest truck here]. Good luck.