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Unread 12-10-2012, 12:09 PM   #1
rmeredit
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Oil Pressure on New Rebuild

I bought my XJ w/ 113k on the clock and the engine was toast. The previous owner had let it overheat, cracked the head, warped the crank and ruined the bearings in the process. So, I rebuilt it completely w/ quality parts/proper lubes:

New Melling cam, Clevite cam/main/rod bearings, Clearwater Cylinder Head, Melling rockers, pushrods, lifters, Sealed Power Hypereutectic Pistons (.020 over), moly rings, Melling stock oil pump, Victor Reinz gaskets, header, Mopar water pump, 2 row radiator, hoses, belt, Melling timing chain kit, crank, distributor, sensors, etc.

The crank was a stock (not turned) crank from a new 4.0 - pulled by 505 performance for one of their stroker engines. It was polished and within spec when I put it in. So, standard main bearings. I plastigauged a few but not all of them (I know, mistake). Same thing with the rod bearings. I used standard bearings but did not plastigauge all of them. They were on the higher side of spec. The block was tanked, checked, bored .020 over and honed to fit the new pistons/moly rings.

Since starting this thing for the first time, it has ran perfectly. It sounds perfect, has power, doesn't burn oil, leak, etc. I broke it in properly (started it, took it up to 2000rpms immediately and varied it between 1750 and 2250 for 20 mins, let it cool down and then repeated). I then drained the break-in oil (Pennzoil 10w-30 and COMP Cams 159) and refilled with another bottle of COMP Cams 159 and Pennzoil 10w-30. I waited 1000 miles before changing again. My only concern with this engine is oil pressure. Since day one, the HOT idle pressure (when it was in the 90deg range) was around 18psi according to the factory gauge. The cold idle pressure when around 50deg was about 55psi.

Tonight I took off the factory sending unit and installed a mechanical gauge.

After driving it around and getting it nice and hot:

Idle: 18psi
1500rpm: 45psi
2000rpm: 54psi
3000rpm: 58psi

After letting it sit idling for 35mins (with the hood shut) and getting nice and warm (JUST under the 210 mark), the oil pressure was at 15psi exactly.

This is with Pennzoil 10w-30 oil, a bottle of COMP Cams 159 (zinc additive/cam break in additive) and a Napa Gold oil filter.

I'm tempted to pull the pan and check the rod/main bearings just to make sure there is no abnormal wear. I would plastigauge all of the rod/main bearings to see where I'm at. I know the mains are only available in STD, .010, .020, etc. There are no .001 bearings to get a tighter fit. But, these are available for the rods & probably the direction I'll go if I need to tighten them up.

I'm also tempted to replace the oil pump with either another stock Melling pump or possibly a Melling high volume (not high pressure) pump.

Thoughts/opinions? I am fully aware this is "within spec" but it varies from what I've seen in past 4.0s that I've had. Maybe with 100k on them but not with 1,200 miles on them... I know that minimum spec is 13psi. Is that acceptable for an engine this "new"?

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Unread 12-10-2012, 05:14 PM   #2
Jason
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I wouldn't worry about those pressure numbers. Seems pretty normal to me.
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Unread 12-10-2012, 08:20 PM   #3
leftlanetruckin
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4.0, perfectly normal.

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Unread 12-11-2012, 02:41 PM   #4
rmeredit
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Normal for a *new* build? You guys are saying that this would be ok for a new 4.0 that just rolled off the lot? It has me feeling like I need to check on it, but not wanting to pull the pan & bearings on a newly-built engine.
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Unread 12-11-2012, 04:12 PM   #5
leftlanetruckin
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OK, when we got our current XJ, it had @70k miles on it. Excellent service history, and so on.
It had the same oil pressure then as it does now, which is crap compared to other rigs and motors.
Even my big rig, with the type of motor it has, has low oil pressure compared to other motors. Been fine for over 800k miles though with anal retentive servicing by myself (had it since brand new).
Stop worrying about it and go for a drive.

Martin
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Unread 12-11-2012, 05:00 PM   #6
slowlowford
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IMO, being you have a 1000 miles on it, everything should be seated pretty good. I would not worry, if it was me. You said your plasti-gauge was on the high side. There really is not anything you can do about that. Unless you want to tear down and go over-sized bearings. I know for the 2.5 you can get .001 and .002 over from napa. I think there was more options but don't remember. But, if you get that deep I would not use palsti-gauge, it gives you a good idea but not perfect. I would use ID mic's and OD mic's, but I am anal retentive. Sorry, for the ramble, but I would not worry about it.
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Unread 12-13-2012, 05:29 AM   #7
jeepdaddy2000
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15 PSI at idle is acceptable.
However, a new motor should be in the 40LB range at hot idle.
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Unread 12-14-2012, 03:29 PM   #8
jokerchief462
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If you are using the gauge in your dash get a real gauge direct line oil pressure gauge and check it then. The electric gauges are not know for accuracy and are really more of a guide so I wouldn;t get too excited until I confirmed with a direct pressure gauge. Book calls for mins at 15-40 at idle and 40-70 at speed this is for my 2.5L.
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Unread 12-14-2012, 09:44 PM   #9
rmeredit
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As I said, I used a mechanical gauge to verify all of this.
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Unread 03-19-2013, 09:58 AM   #10
rmeredit
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3_2013 Update

Well, I figured I would update this post in case anyone comes across it. I know there are a million threads out there about oil pressure...

I've put about 2400 miles on this engine since the rebuild. Honestly, it ran like a raped ape but never satisfied me because of the oil pressure. I put so much time/money into this engine and I want it to last.

When I built it, I used a stock 4.0 crank (same casting as the original) that had been checked for warp, cleaned and polished. So, the journals were slightly smaller than stock due to the polishing. Honestly, I never realized .001 or .002 main bearings existed (dealer only) - so I went with Clevite tri-metal bearings in STD size. As stated above, the tolerances were within spec but on the HIGH side.

After contemplating my options for a while and doing a ton of research, I decided to tear into it this weekend. I purchased Mopar (made by Mahle-Clevite btw) .001 and STD main bearings, Clevite .001 and STD rod bearings and a new Melling M81A (standard volume/pressure) oil pump.

I rolled out the STD main bearings (one at a time) this weekend and replaced them. The crank journals looked/felt perfect - no scoring at all (as I expected). I rolled in new .001 bearings and plastigauged every main, expecting to have to possibly run a mix of .001/STD on each journal. Not to be. All mains were at .002 or slightly under. Right on spec as per the FSM. Awesome!

I did the same with the rods and realized I needed to use the .001 bearings top/bottom as well. All rods are .0015-0020. Awesome, also!

It was a real PITA to do this while laying under the vehicle on my <bad> back. Rolling in one bearing at a time and taking the time to plastigauge them, take caps back off, measure, apply assembly lube, reinstall, etc. - took FOREVER. The rods were a piece of cake.

If you're going to try this yourself, make sure you take your time and have the proper tools (wood tongue depressor, cotter pins to make rollout tools, a plastic "punch", .001-.003 plastigauge, FSM, etc.).

I replaced the RMS while I was in there. Obviously it wasn't needed as it only had 2400 miles on it but I'm anal. I also replaced the oil pump (with an identical pump, primed with vaseline) and installed a new screen (also 2400 miles on them). Lastly, a new felpro oil pan seal was used. I don't like reusing parts. ;-)

After finishing up, I filled the engine with some Rotella T5 10w30 and 4oz of COMP Cams 159 (zinc additive) along with a Purolator PureOne oil filter. I fired it up and IMMEDIATELY saw the difference that .001 less clearance in rods/main bearings. My oil pressure at cold start was up in the mid-high 60s. I drove it around to heat the engine up to operating temps and then brought it home to cool down. The oil pressure never dropped below 38psi, even at hot idle. I drove it for about an hour the next day and never saw less than 38psi. This thing runs perfect, sounds perfect and is nice and tight now.

Are some people going to have a stroke over this? Sure. Am I a happy mofo - Yup.

Any questions/comments? I'll keep this post updated in the future so everyone knows if this was a good idea or not.

Last edited by rmeredit; 03-19-2013 at 10:00 AM.. Reason: Grammar
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Unread 08-19-2013, 03:12 PM   #11
rmeredit
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5 month update. Still running awesome & the oil pressure remained nice & strong during the hot months. I never see pressure below 35psi w/ 10w30 Rotella T5 (blend). I'm going to have an oil analysis done after this coming change & will report back. I'm not doing it b/c of the mileage on the oil, just curious.
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Unread 08-19-2013, 05:54 PM   #12
cruiser54
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Gotta ask. What brand of oil filter did it have on it for break-in and right after that?
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Unread 08-19-2013, 06:07 PM   #13
stephenfarris
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Mine runs @40psi at idle-sometimes drops to 35psi when very hot. Always 50-60psi on cold idle and running. Doesn't matter if I run 30 or 40wt oil.
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Unread 08-19-2013, 08:17 PM   #14
BIGBADWOLF
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Quote:
Originally Posted by rmeredit View Post
Well, I figured I would update this post in case anyone comes across it. I know there are a million threads out there about oil pressure...

I've put about 2400 miles on this engine since the rebuild. Honestly, it ran like a raped ape but never satisfied me because of the oil pressure. I put so much time/money into this engine and I want it to last.

When I built it, I used a stock 4.0 crank (same casting as the original) that had been checked for warp, cleaned and polished. So, the journals were slightly smaller than stock due to the polishing. Honestly, I never realized .001 or .002 main bearings existed (dealer only) - so I went with Clevite tri-metal bearings in STD size. As stated above, the tolerances were within spec but on the HIGH side.

After contemplating my options for a while and doing a ton of research, I decided to tear into it this weekend. I purchased Mopar (made by Mahle-Clevite btw) .001 and STD main bearings, Clevite .001 and STD rod bearings and a new Melling M81A (standard volume/pressure) oil pump.

I rolled out the STD main bearings (one at a time) this weekend and replaced them. The crank journals looked/felt perfect - no scoring at all (as I expected). I rolled in new .001 bearings and plastigauged every main, expecting to have to possibly run a mix of .001/STD on each journal. Not to be. All mains were at .002 or slightly under. Right on spec as per the FSM. Awesome!

I did the same with the rods and realized I needed to use the .001 bearings top/bottom as well. All rods are .0015-0020. Awesome, also!

It was a real PITA to do this while laying under the vehicle on my <bad> back. Rolling in one bearing at a time and taking the time to plastigauge them, take caps back off, measure, apply assembly lube, reinstall, etc. - took FOREVER. The rods were a piece of cake.

If you're going to try this yourself, make sure you take your time and have the proper tools (wood tongue depressor, cotter pins to make rollout tools, a plastic "punch", .001-.003 plastigauge, FSM, etc.).

I replaced the RMS while I was in there. Obviously it wasn't needed as it only had 2400 miles on it but I'm anal. I also replaced the oil pump (with an identical pump, primed with vaseline) and installed a new screen (also 2400 miles on them). Lastly, a new felpro oil pan seal was used. I don't like reusing parts. ;-)

After finishing up, I filled the engine with some Rotella T5 10w30 and 4oz of COMP Cams 159 (zinc additive) along with a Purolator PureOne oil filter. I fired it up and IMMEDIATELY saw the difference that .001 less clearance in rods/main bearings. My oil pressure at cold start was up in the mid-high 60s. I drove it around to heat the engine up to operating temps and then brought it home to cool down. The oil pressure never dropped below 38psi, even at hot idle. I drove it for about an hour the next day and never saw less than 38psi. This thing runs perfect, sounds perfect and is nice and tight now.

Are some people going to have a stroke over this? Sure. Am I a happy mofo - Yup.

Any questions/comments? I'll keep this post updated in the future so everyone knows if this was a good idea or not.
I can see that you are kinda obsessive and that is OK but this should calm alot of peoples fears about low oil pressure. Before you tore it down the second time the clearances were in spec, on the high side but within spec. Which means an engine with low pressure can still be within specs. .001 above optimal, (if it is this way for all bearings) will accumulatively have a drastic effect on pressure but in reality this should not be anything to worry about.
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Unread 08-20-2013, 09:22 AM   #15
rmeredit
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Quote:
Originally Posted by cruiser54 View Post
Gotta ask. What brand of oil filter did it have on it for break-in and right after that?
Napa Gold (WIX) during initial break-in and Purolator Pure-One since then (only because I got several of them at a great deal). I usually run Napa Gold only.
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