I am going to confirm my readings are accurate as soon as I get the chance but I'll assume they are. The readings were the reason I noticed a problem initially, long story short I needed rebuild. The shop I used took care of me and I have a warranty should I need to go back.

I live in Michigan so right now it is a bit cold. Engine starts up oil pressure reads 80, cool. Drops to about 60 after the first 20 minutes of driving, 40~ while idle. Still, all is well. However after about another 10-15 minutes things change. While driving it is now closer to 35 and idle closer to 17 lbs. It does surpass 40 lbs while accelerating but then settles 30-35 when my speed becomes constant. I know 13 is the lowest spec calls for and 37-70 lbs >1600 RPM's. A lot of posts suggest this is normal for a worn engine, but if all my parts are new...should I set up a date with the shop?

Worth mentioning: It's an '01 XJ. Old parts had 200k on them. I'm looking for the paper that read what WAS NOT changed in the rebuild...will update.

 

I'd be more than a little suspicious of your pressure sender.

 

Frankly, your pressure readings sound normal to me.

Many people think high oil pressure is desirable. It is not. Similar to the way high blood pressure is not good.

Pressure is resistance to flow. You want a good flow to lubricate and cool the engine parts. Therefore, lower pressure, up to point, is a good thing.

I would be a lot more concerned what was done about your original 0331 head. I would never reuse or re install one of those during a rebuild.

 

Is pressure sender synonymous with sending unit? heard they're pretty faulty in the xj's. Excuse my n00bness. I'm learning bear with me :P

^This is what I believe as well. but my buddy who is a "Jeep god" is convinced I should not be fluctuating this low on new parts. At what point should I be concerned? Good point on the head though, I will call the shop tomorrow and ask about the 0331. Is there an easy way to tell just by popping the hood?

 

WamBaLam,

What shop did you use to rebuild that engine?

 

x2 Oil pressure after a rebuild is not a constant....too many variables. Your numbers indicate that your moving oil. Think of it this way; high readings indicate the reserve capability of the pump and is the dead zone of flow. Another analogy is pressure is like a spring pushing on something.

 

Totally agree.

 

Purchase a $30 oil pressure gauge from the local parts place. Install it per the instructions but carefully ziptie it up in the engine compartment away from heat etc. Drive around. Find a parking lot. Open hood and read needle. Or carefully route into cab and read as you are driving.

Find out that the original sending unit is worn out and replace it.


My 1992 4.0 has 2-3PSI at hot idle and about 20PSI max at 75MPH. Been that way for YEARS now. No noises. No problems. Running 15w40 Rotella.

 

Fairway Engine Exchange, in Sterling Heights. So far I'd recommend them. The only problems have come from me over stressing this oil thing. Buddy with a lot of XJ hours under his belt said I'm the reason they started using dummy gauges ha.

Sending unit is a pretty cheap part, IIRC it's pretty accessible, over by the filter. I might just slap a new one in. I'm not one for throwing parts at a problem but in this case it's not a huge hit.

 

80# on the gauge is on the full-right stop. That's typical for a failing sending unit, at least until the oil warms up. Pressure sender = same thing. Mounted to the oil filter housing.