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oil pressure, band-aid fix.....


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I've been noticing the oil pressure slipping off on the 4.0 the more I drive it. At cold start it's well over 40 psi, but as it warms up and especially if I take a highway trip it ends up dropping down into the 10-20 range, sometimes a bit lower at idle (watched the needle drop to 0 once sitting at a stoplight.....not cool). It does rise and fall with engine rpm's, but only gets up to about 30 at the most. 10W40 Castrol dino oil with a Purolator filter, too (that's all I run on my junk).

 

On a whim I changed out to Castrol 20W50 over the weekend, and what an amazing difference. Cold starts I get immediate pressure, 60-70 psi, and it only drops down to 25-30 ish when warm. Valvetrain is kinda quieter too :D

 

Future plans are a stroker out of the 4.0 HO block from my neighbor's YJ that I swapped a couple months ago, so I'm just gonna keep running the thick stuff for now until I get that built and installed.

 

Jeff

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How many miles are on your engine?

On one of my other vehicles I was getting extremly low oil pressure readings on the guage. I wasnt hearing any "ugly" noises like from oil starvation symptoms so I changed the sending unit, problem solved, oil pressure back in the normal range.

IMHO After rereading your post I would think about swapping out the sending unit.

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200K + (not exactly sure, I got it from Pat when I did the 4.0 swap).

 

I already changed the sender with a new one, unfortunately :( ...that only raised the reading a couple psi.

 

No real ugly noises from the bottom end, just the usual 4.0 racket. But the top end is a bit clackity (especially with the steel valve cover I'm running).

 

Jeff

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Jeff, I switched the '88 XJ from 10W40 dino oil to 20W50 synthetic at about 180,000 miles for the same reason. Mine wasn't quite as low as yours when warm, but when new it ran 50+ psi at highway cruise, so the decline was obvious. The change to 20W50 brought it back up to 40-45 psi highway, and it has stayed there for several years and over 100,000 miles. (I'm now at 282,000). But we get pretty cold nights here in winter, so when I discovered that Castrol has a 5W50 full synthetic, and that VW and BMW were using Castrol synthetic as their OEM oil and recommending a 15,000 mile change interval, I switched to 5W50 Castrol and that's what I've been running in the old heaps. I use the same oil in the new Cherokee, but for that one I use the factory-recommended 5W30.

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That's refreshing news Eagle, thanks......

 

jeep_freek, I've been toying with the idea of running some Lucas in it to see what it does, I used to run it and some Restore on the old 2.5 occasionally. Maybe I'll try a quart and see, can't hurt any I figure :D

 

The one thing that I had been noticing with the 10W40 is that it kept getting REALLY thin when it got hot.....I mean thin like water-thin (and it was new oil even, less than a couple hundred miles). If I parked it and let it sit for a couple of hours and it cooled down I would get good pressure back, until it warmed up again. Aside from just about doubling the price, have oil manufacturers changed formulations lately (aside from the ZZDP issues)?

 

Jeff

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