Oil pump?

[fiatslug87]

’88, 4.0, 5 speed, 4x4

I was changing the oil and when I pulled the filter it was dry! It looked as though no oil had ever reached inside the filter. I’m assuming it’s the oil pump; it can’t be a bad filter can it? It’s a Mobil-1 filter running Mobil-1 10w30 oil. The factory oil pressure gauge has been reading 20-30 psi, I know this is lower than my other two MJs which run 40-60 psi but I just thought the gauge or sensor was inaccurate. The engine hasn’t been running hot (unless that gauge is also off) so what other symptoms should there be?

What’s the manufacturer and part number for the one piece oil pan gasket? And are you positive it will fit?

Has anyone had problems with any after-market oil pumps? I don’t want to replace it again.

Is the most difficult part removal and installation of the oil pan?

Any and all input is greatly appreciated.

[Eagle]

If the engine is getting oil, then the pump is pumping. There is a by-pass for when the filter gets plugged, so perhaps your by-pass is malfunctioning.

 

The one-piece gasket is a factory item. They started using it in model year 1994, I think. If not '94 then '95. Should also be available from aftermarket brands such as Fel-Pro.

 

Yes, it fits.

[HOrnbrod]

If the engine is getting oil, then the pump is pumping. There is a by-pass for when the filter gets plugged, so perhaps your by-pass is malfunctioning.

 

Where's the by-pass Eagle? Somewhere in the filter adapter assembly? I didn't now there was one. :oops:

 

I was changing the oil and when I pulled the filter it was dry! It looked as though no oil had ever reached inside the filter. I’m assuming it’s the oil pump; it can’t be a bad filter can it? It’s a Mobil-1 filter running Mobil-1 10w30 oil. The factory oil pressure gauge has been reading 20-30 psi, I know this is lower than my other two MJs which run 40-60 psi but I just thought the gauge or sensor was inaccurate. The engine hasn’t been running hot (unless that gauge is also off) so what other symptoms should there be?

 

Are you using the large Mobil M1-301 oil filter?

[fiatslug87]

Are you using the large Mobil M1-301 oil filter?

No, I'm using the M1-207.

 

I'm also interested in more information on the by-pass.

[Eagle]

The illustration I have from the '88 FSM shows it in the block, behind where the oil filter adapter mounts to the block. That's where I remember it being from the old AMC days. Problem is, they show it in detail for the 4.2L engine, but that engine has the filter mounted directly to the block the way the old AMC engines were set up. I am left to assume (which is always dangerous) that the same parts are in the block behind where the 4.0L oil filter adapter bolts on. It's basically a spring and a plunger.

 

I really wish I had a functional scanner ... but I don't.

[HOrnbrod]

The illustration I have from the '88 FSM shows it in the block, behind where the oil filter adapter mounts to the block. That's where I remember it being from the old AMC days. Problem is, they show it in detail for the 4.2L engine, but that engine has the filter mounted directly to the block the way the old AMC engines were set up. I am left to assume (which is always dangerous) that the same parts are in the block behind where the 4.0L oil filter adapter bolts on. It's basically a spring and a plunger. I really wish I had a functional scanner ... but I don't.

 

Thanks. I've been through my 91 FSM, and it doesn't show anything like that. I know the newer screw-on filters have built-in bypass valves usually set at 11-17 psi depending on the mfg. so maybe the the internal by-pass has been abolished.

[Eagle]

Thanks. I've been through my 91 FSM, and it doesn't show anything like that. I know the newer screw-on filters have built-in bypass valves usually set at 11-17 psi depending on the mfg. so maybe the the internal by-pass has been abolished.

I doubt it. I think the quality of the service manuals is inversely proportional to the size. The by-pass was pretty well covered in the old AMC shop manuals, which is how I know about it. It is mentioned in the '88 FSM for the 4.0L engine. In the '94 FSM, which covers both the XJ and the YJ (Wrangler), they don't show it or mention it under the 4.0L engine but they do show it under the 2.5L engine. I don't think they would eliminate it from one but not the other.

 

I guess I have to dig out a 2000 FSM and see if they discuss it in that.

 

AFAIK oil filters have always had an internal by-pass.

[fiatslug87]

Thanks guys. The '90 FSM mentions an "oil pressure relief valve assembly" which consists of a spring and plunger but they are located in the oil pump body. It states on page 9-79 6) Remove the cotter pin and slide the spring retainer, spring and oil relief valve plunger out of the pump body. But no diagrams of it. So again this leads me to believe if I replace the oil pump it should fix my problem. I picked up the 1-piece gasket and the oil pump should be here today.

[StevenH]

Oil pumps do have a bypass valve but the oil that get's bypassed goes right back out into the pan and doesn't circulate through the engine.

[HOrnbrod]

Thanks guys. The '90 FSM mentions an "oil pressure relief valve assembly" which consists of a spring and plunger but they are located in the oil pump body. It states on page 9-79 6) Remove the cotter pin and slide the spring retainer, spring and oil relief valve plunger out of the pump body. But no diagrams of it. So again this leads me to believe if I replace the oil pump it should fix my problem. I picked up the 1-piece gasket and the oil pump should be here today.

 

Yes, I did see the oil pump pressure relief valve (non-adjustable) in my 91 FSM. Do the new oil pumps come with a strainer?

 

Most all screw-on type filters have the internal bypass, some set at different pressure ranges by mfg. But the old cannister-type filters did not AFAIK.

[fiatslug87]

Do the new oil pumps come with a strainer?

If you mean the pick-up tube and screen, you can get them with or without. I got a high volume one that came with the tube. I'm not sure how you would reuse the old tube because its a pressure fit. I had to cool the tube and heat the pump then use an open-end wrench (around the tube's collar) and hammer to drive the tube into place.

 

I just finished replacing the oil pump; my pressure is now 60 at start-up and 40 while driving. I felt the top of the filter (same one that was on before) and it was pretty hot so I think the oil is flowing through it now. I’ll take it off tomorrow to verify. I’m very happy except for what I found in the oil pan, a whole lot of metal shavings, about a 4x4 square ¼ “ thick in a zip-lock bag. The old oil pan gasket was a 1 piece so the PO must have been into it within the last 10-12 years. Now I’m afraid to compression test it, I guess a rebuild is closer than I thought!!! Glad I got it done today since it just got tagged by the city police for being on the street too long. I wish I had a large work area; I’m seriously envious of JeepcoMJ after seeing his “Today's accomplishments” post in The Pub forum. Thanks for all the help.

[JeepcoMJ]

I just finished replacing the oil pump; my pressure is now 60 at start-up and 40 while driving. I felt the top of the filter (same one that was on before) and it was pretty hot so I think the oil is flowing through it now. I’ll take it off tomorrow to verify. I’m very happy except for what I found in the oil pan, a whole lot of metal shavings, about a 4x4 square ¼ “ thick in a zip-lock bag. The old oil pan gasket was a 1 piece so the PO must have been into it within the last 10-12 years. Now I’m afraid to compression test it, I guess a rebuild is closer than I thought!!! Glad I got it done today since it just got tagged by the city police for being on the street too long. I wish I had a large work area; I’m seriously envious of JeepcoMJ after seeing his “Today's accomplishments” post in The Pub forum. Thanks for all the help.

 

:-/ metal shavings aren't good...what kinda razor have you been using :roll:

 

anyways yeah it's nice to live on a "farm" but my mother doesn't seem to understand...she married a mechanic, and she's mad about all the "junk" laying around. generally we clean house every 4 months or so...and where I park the parts trucks no one can see, yet she throws a blooming fit about it. I understand though, that it's her house. don't push the issue.