Low Oil Pressure; What should I do?

I have a 1974 CJ-5 with a 258 inline 6 engine in it. Speedometer says 97,980 miles, but I am not sure that it ha the original engine.

I have a newly installed mechanical oil guage, and I have bled the line. Both the new gauge, and the old gauge say the same numbers.

I have 40 PSI at idle, cold.
When the engine is warm, I have 3 PSI to 5 PSI MAX at idle, and 23 PSI at 2000 RPM.

Did a compression check, from right to left looking at the spark plugs I have:
100 PSI, 105 PSI, 100 PSI, 145 PSI, 135 PSI, and 100 PSI.

I hear no valve wrap except when the engine is warm, and at an idle, I hear very slight wrapping.

Should I.....

A) Run the jeep, it will be fine
B) Put a new oil pump in it
C) put new lower end bearings in it
D) put thicker oil in it and run it

Thanks for the input, very much appreciated!!

 

From the TSM...

The date code on the right side of the block between #2 and #3 cylinder. First number is year (i.e. "7" is '74), then month, then engine type (A is 258 ), then day of month.

Your compression should be in the 150psi range for a 258 with max variance of 20 between cylinders.

Normal operating oil pressure is 13 psi @ 600 rpm, 37 @ 1,600.

So, having said that, it looks like you're engine is a bit worn out and tired, and might need a rebuild to keep it happy. An oil pump upgrade would probably help, but it won't answer the compression issues.

I guess the answer is, it depends on what you want the Jeep for and if you care if it should up and quit on you?

 

I'm thinking an oil pump won't help much ... the 258 oil pump isn't usually a problem.

First, I'd run the compression check again after adding a teaspoon or so of motor oil to each cylinder, through the spark plug hole. A pump oiler works well for this. The compression numbers you list aren't terrible, but they indicate to me that you have worn rings (a tired engine). The low cylinders should come up some with oil on top of the rings.

Next, I'd get rid of your Fram oil filter - assuming you have one - and replace it with a Wix or Napa or STP. There are other good ones, but not Fram. If you replace a Fram filter, your hot idle oil pressure will usually come up quite a lot.

I would take the pan off and inspect the rod bearings. Wear in a long stroke engine like the 258 (with high piston velocities) should show up there first. Pretty sure you can use Plastigage on the rods with the crank in place.

And baby it. Keep the RPMs down, and keep a light throttle foot. The hot idle oil pressure would worry me, but as long as there's no metal-to-metal contact, it'll keep going.

 

A general rule of thumb is all cylinder's compression numbers should be within about 75% of one another. You are sitting at about 68% between the best/worse numbers. I would consider rebuild time approaching.

As previously mentioned, an oil/filter change can work wonders in oil pressure.

Beware of fluctuating oil pressure too as that can be an indicator of a bearing on its way out.

 

What are you running for oil weight? It may be worthwhile to switch to 15w 40.

 

good old 30 weight

 

Thanks for the information!!!! Very helpfull. I knew the PSI shouldn't have quitte so much varience.

Yeah, I never really beat on the jeep anyway. But I do have a napa filter. I have never had good luck with fram, and will never go back.

Yeah, I think that is what I am going to do. I was origonally going to replace the lower end bearings, but with the compression being so far off, I think I am justt going to run it easy untill it either dies, or I feel like doing a complete engine overhaul.

I was running 10-40. I changed the oil this weekend to 20w-50. It brought it up a little, but not as much as I was hoping.

 

chuck some lucas at it