Oil Pressure Sending Unit

So after a little bit of research, I've come to believe that my oil pressure sending unit may have started to fail after about 200k miles. Mostly I'm just looking for a couple of opinions as to whether or not that's a good assumption.

Symptoms:

I've had my 89 xj (4.0l, ax15, np231) about a year, not too many problems so far. It was very well maintained by the previous owner who had it from 50k-200k. In my experience this last year, oil pressure runs between ~40-50psi cold, and ~20-40psi after long drives (25+ minutes), never goes any lower than that. Just changed the oil a few days ago, and it's been running a little higher, about 45 to 55 or 60psi, but I haven't really gone anywhere to get it warmed up good (I live about 1 mile from my job, just been driving home and back since I changed the oil on Wednesday 5/2).

Driving home today about 25mph I looked down and noticed the pressure read 80psi. I took my foot off the pedal and it fell to 50, hit the gas barely (~1.5k rpm) and it jumped to 80 in a couple seconds. Driving down the street it seemed to jump around randomly a few times, up or down 10 or 15psi at a time. Most of the time it would respond to me revving the engine (up when I revved it, then fall back down when I took my foot off), but sometimes it would just stick at one pressure for a moment.

I got home, turned it off for a minute, then restarted it. I let it run for a minute or two and it sounded normal (some lifter tick, but no different than its sounded since I've had it, they go away mostly after 5-10 minutes of driving). Pressure read 40psi, when I hit the gas it went up to 60psi, but never higher, even at 4k rpms.

I've looked at a bunch of posts, and they've pointed me toward the oil pressure sending unit. My gauge has always read 0 when the engine is off to my knowledge, but it read about 5 when I put the key to accessory while testing this hypothesis. I didn't move with or without the key in the ignition, just sat about 5 until I started it again, then it went up to 40ish. Also, I noticed 2 or 3 very small drops of oil on the ground when I got home, looked like they'd dripped off the starter. I read in one post that when the OPSU fails, it can leak some oil out the end where the plug connects. Does this seems likely at all?

My other thought for the high pressure was clogged oil passages, although the oil has been changed regularly by both me and the PO, and I didn't notice any different sounds from the engine to indicate something not getting oiled correctly.

Does it sounds like I'm heading in the right direction?

Thanks for reading all of that, any opinions/comments are welcomed. :wave1:

lots of things to comment on in this post, i'll answer what comes to mind right off the bat. oil dripping from the starter is likely from the orings on the oil filter adapter housing, there are 3 orings in that housing and after awhile they all start to leak. I would bet that is the source of your leak. when the sensor itself is leaking it tends to spray profusely out of the connector.

15-20 psi warm at idle is normal. I would say you are not having a problem and the 50-60 psi readings are well within spec for a 200k mile engine. the sensor is cheap and easy to replace though so if you suspect it being faulty then just change it - especially if you don't have a record of the last time it was swapped out.

good luck, welcome to the forum. Lots of good info here if you search and read read read. just about every question from original equip to the wildest of modifications has been answered many times before. the search function of the forum software is kind of a pain in the butt to use, so check out this guide written up by one of our members to get better results and find what you're looking for faster: http://www.naxja.org/forum/showthread.php?t=73349 this applies to all forums running the vBulletin forum software and not just ours.

Happy hunting

The o-rings were replaced at 120k in 10/2000 according the the service records, although I suppose they could be worn out again after 12 years. I didn't notice a leak when I looked at it from the top, but I'll climb under there tomorrow to see from underneath.

best bet is to grab a couple cans of engine cleaner and clean it up, then start looking for where the oil starts showing up again

The sender would be my prime suspect. If it got knocked a bit when you were changing the filter, it might contribute, though it's not as easy to break the sender doing this on an 89 as it is on the later ones. The leakage could be from it, or from elsewhere, but senders do leak frequently. You'll need to keep an eye on it. Clogged oil passages aren't very likely, especially if the reading keeps changing. Your slight rise in normal pressure is not uncommon if you've bought a different brand of filter, or different oil. I always got slightly better pressure with Wix, Bosch and K&N filters than with others.

Before you go too far, make sure the wire to the sender isn't touching ground somewhere and messing up the readings. Your gauge should read 0 disconnected, and max when shorted to ground, so it might jump up if a cracked wire is grounding through a layer of dirt and oil. If with engine off, you can't get the reading down to zero while fiddling with the wire, it's pretty likely the sender.

Change the sender. $15. Fix the leak. I'll betcha a dime the two are not related. Then you're only out the $15.10.