So, just a few quick questions because the search option and google are failing to yield answers. This is for my '91 XJ with 204K miles.

What could be a potential cause for sudden low oil pressure? I understand that worn out bearings are the usual cause, however I would assume that low oil pressure due to bearing failure would be gradual and over a period of time correct? My oil pressure dropped LITERALLY overnight. One day, great pressure, the same as for the past 2 years since I owned her. The next day, low pressure issues. Literally overnight.

Another cause I have been researching is oil filter failure. I've heard that certain issues or clogging of the oil filter would cause low pressure.

I also have heard that clogged oil passages or a clogged pick-up could cause problems. Is there any good way to flush the engine? I've been told by many that those Motor Flushes from A/Z and NAPA aren't very realiable.

Lastly, I guess the only other thing if not bearings would be oil pump. Could it fail as quickly as this issue arrive? I went from 60 psi cold start idle to 45ish cold idle and then it goes up a tad with accel, and went from 25 psi hot idle 45 hot accel at 2000rpm to 18-20 hot idle and 35 max with accel, even past 2000 rpm.

I don't want to throw in the towel with the ol' girl. She's served me well, and was mis-treated (by what I can tell) from the PO. I'm with this XJ for the long run.

 

Confirm the pressure with a new sending unit or a mechanical pressure gauge.

 

Replaced the sending unit (Autozone sadly. Stealership tried to tell me that all they had was a sender for the dumby light). I am tyring to find a good mech pressure gauge (prob just take it to the mechanic) because the cheapo thing I bought from A/Z also is crap.

 

dont forget warmer temperatures are getting here so your oils going to be a little thinner at cold start up ,which will causes lower oil pressure at start up . The oil pressure readings your getting are well with in the specs for a 1991 engine with 200,000 miles `

 

But would it really be normal to settle at 35 psi? I mean, I can get up towards 3000 rpm and the pressure barely goes up if at all.

 

mine after warm up runs about 37 when on highway im at 199,000 miles also and around 18 to 20 at idle i fell that damb goodfor this many miles

 

But even so, would it happen so quickly? I would think that it would have been a slow decrease over time.

 

First the pressure you have now is pretty much normal. Have you changed the oil or filter recently? Did you change brands of filter or oil weight?

 

Do an oil and filter change if you can afford to do one now. Drain the oil into a clean pan and Look for any sediment/metal particles in the bottom of the pan. This will tell if you had a bearing wear issue.

There also could be something stuck in the bypass of the oil pump (typically a ball pressed into a seat by a spring that opens at ~80 psi and prevents too much oil pressure in the system). If this happened, it would bleed pressure off the system constantly. Other than dropping the pan and cleaning/replacing the oil pump, the only way that MIGHT clear it is to rev it up high (below redline) while the oil is below operating temp and thick. Please exhaust all other possibilities before trying this!!!! I would hate for you to ruin your engine when it turned out to be something else.

Hope this helps

 

This past oil change (about 1400 ago) I used a bottle of Lucas and a Purelator filter, both of which I had not done before.

If it came down to the pump being suspect, I would prob just drop the pan and replace the pump. I wouldn't want to redline it and have something else crap out.