Oil Pressure?

I start my jeep up and automaticly the oil presure gauge reads 60, it usually stays this way for probably 20 min. or so. it this bad for the engine? if so what are someways i can fix this? then it returns to just a little over 40

i have a 1995 with the inline 6, i get the oil replaced every 3,000 miles i have an oil leak or two but nothing huge, my oil level is where its suppose to be at. one odd thing is i seem to have a lot of drops of oil on top of the oil filter. another thing is i always seem to smell oil when i'm by my jeep.
i dont know that much about engines so i hope this info i gave you about it is helpful

Your oil pressures are normal. Oil is more viscous when cold so you'll always find the oil pressure is higher when the engine's cold and it drops as the engine warms up.
Oil leaks are common on high mileage 4.0's and that would account for the smell. In your case, it's quite likely that the oil is leaking from the oil filter housing o-rings. Replacing them is easy. Just unbolt the oil filter housing from the block, remove the old ones, and insert the new ones.
Another common site for oil leaks is the valve cover gasket. Less common are the rear main crankshaft seal and the oil pan gasket. A bit of oil "sweat" on the passenger side of the block below the level of the head gasket is normal.

The oil sending unit in the wifes 95, does pretty much the same thing as you´ve discribed. I always figured it was a faulty oil pressure sending unit.
If you disconnect the wire to the sending unit, the needle goes up all the way (the higher the resistance, the higher the reading). Could be too much resistance in the sending unit or a faulty connection (loose, oil covered) connection beween the sender and the gauge.
Hooking up a mechanical oil pressure gauge for a few minutes, may give you a true idea of what´s going on, with your oil pressures.
Fixing the sending unit on my wifes 95, is kind of far down my list of things to do, I usually just watch to make sure it doesn´t go all the way up to the stop or all the way down to no pressure.

My 95 reads pretty high on startup too, but it settles down later, so I figure it's just not worn out yet (only 211 thousand miles). As long as you have a consistent reading, that seems to respond to engine speed and temperature, it really doesn't matter whether or not it's that accurate. You'll get to know what's normal, and be alerted when it isn't.

For the oily smell, there are several possible sources. Could be the rear main seal, the oil pan, the valve cover gasket, the oil filter adapter, or the pressure sender, or any combination of the above. All of these things seem to drop a little oil on the exhaust pipe where it crosses behind the engine, and it burns off when you restart. Unless the leak is bad, I wouldn't worry much. Check the valve cover bolts and the oil pan bolts for tightness, and let it go.

I have a 1994 XJ with 115,000 miles my oil pressure at start is about 60 and after while driving it's about 40 and while on idle its about 20. Is this good pressure? The sending unit is new, new oil filter, new oil (30W).

hasta

The pressure lubricated parts are the engine bearings and lifter bores...the oil serves as hydraulic fluid in the lifter internals...what bleeds past and goes up the pushrods gets splashed around by the rockers...everything else is splash lubricated except the cam lobes...oil exiting the connecting rod bearings thru a channel machined in the rod is sprayed in the general direction of the cam lobes.

20 psi is a fuzz lower than the published norm of 25 psi at idle...still not a major worry...double check the actual pressure with a mechanical gage...I would change to a 20-50 oil (I'm a Castrol GTX fan) and throw in a pint of Lucas oil stabilizer just for grins and giggles.

Although the dealer said his guys put a gauge on it and it's "OK", but no numbers were mentioned. I'd love to see 60. Mine reads 40 cold and 15-20 hot. I dont' like it that low, but I'm hoping it's the sensor and not a plugged screen.

How low can it go, and is this too low?

MudDawg said:

The pressure lubricated parts are the engine bearings and lifter bores...the oil serves as hydraulic fluid in the lifter internals...what bleeds past and goes up the pushrods gets splashed around by the rockers...everything else is splash lubricated except the cam lobes...oil exiting the connecting rod bearings thru a channel machined in the rod is sprayed in the general direction of the cam lobes.

20 psi is a fuzz lower than the published norm of 25 psi at idle...still not a major worry...double check the actual pressure with a mechanical gage...I would change to a 20-50 oil (I'm a Castrol GTX fan) and throw in a pint of Lucas oil stabilizer just for grins and giggles.

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Thanks MudDawg I'll try the 20-50 next oil change.

Factory says anything 13 and over is fine at an idle when hot and 35+ at cruise speed.

Oil is always thicker when cold, which equates to higher pressure when you first start a cold engine. Normal highway speed oil pressure for just about every new-ish XJ I've ever seen is 50 to 55 psi. Yeah, 60 psi would be nice ... dream on, it ain't gonna happen.

None of you guys who asked have any worries. The factory service manual (FSM) specs are (for a warm engine) 13 psi minimum at 650 RPM idle, 37 to 75 psi above 1600 RPM.

I know someone's waiting out there to chime in with "You're supposed to see the oil pressure rise 10 psi for every 1000 RPM." I've heard that, but I have never yet seen an engine where it happens.

My XJ idles at about 25 psi. If that rule-of-thumb was correct, at 1600 RPM I should have 35, at 2600 RPM I should have 45, and at 3600 RPM I should have 55. I have a 5-speed. Highway cruise at legal speeds is 2000 RPM or a bit less, and the oil pressure has peaked at that speed. If I downshift and run the RPMs up to 3500 or 4000 RPM the oil pressure doesn't do up another 20 pounds.

Basically, if you have 15 psi or more at idle and 40 psi or more at highway speed, you're good to go.

The oil filter also has and effect on it. I just put in a gauge panel back in january or so in my 98XJ, so I have no previous numbers to go by. At the time I had a K&N filter on it, it ran around 60 at hiway, 20 at idle when I first put the cluster in. Changed the oil and put a Mopar OEM filter on it, hiway dropped to a shade over 40, idle dropped to ~15. Just did another oil change with a Mobil-1 filter, hiway ~45, idle ~15. This is with mobil-1 10w30. Curious to see what happens next change when I go back to a K&N filter even though I have a half dozen Mobil-1 M1-204's on the shelf... both TJ's take the same filter as the 4.0L XJ even though the TJ's are 2.5L 4 bangers... Oh, it has ~203,000mi on it

the actual common rule on oil pressure is to have 10 psi for every 1000 rpm ie. 10 psi at 1000rpms 40 psi @ 4000 rpm etc. more important than actual pressure is to have an nice clean unairated supply feed to all bearing 100% of the time that vehicle is running

Is the sender before the filter or after in the flow? From the looks of things (on my 89), it's before.

In that case, the higher pressure reading relates to less flow. With a good pump (even with age) pressure and flow are _inversely_ related. The more restriction, the less flow and higher pressure. That's why pressures drop as engines wear and clearances open up - less restriction. There's also a relief valve on the pump to prevent pressure over some amount. Theoretically, you could plug it up after the sender, have no flow, but full pressure reading. It would all be dumping back into the pan at the pump, out the valve. That's also why the thicker oil when cold has higher pressure.

As the engine wears, it has less resistance to flow because of the gaps and the pressure drops. That's what worries me about mine - 15-20 psi at all speeds (5w50 Syntec). So much wear there's no resistance anymore. Maybe it's the sender...

The other pressure drop reason would be pump problems, but they're so simple it's usually work-or-fail in my experience.

You could try a really cheap filter with less filtration as a test to spin on at next change. Assuming it had less resistance because it didn't filter much, the pressure should read lower. The higher filtration filters would give higher back pressures.

You could also open up the filler in the valve cover and get a feeling for flow by watching it flow over the rockers. Then you could compare flows too. I've got minimal flow at idle - another indication of excessive wear (it's blowing out of the bearings lower down).

BTW, I used to put 20w50 or 20w40 in my Mustang because of wear, but after I ran it with the covers off to adjust the rockers, I'll not do it again. It took a full 2 minutes when cold (cool - 70F or so) for oil to reach the top!!! 5w something from then on. It gets up there faster, but since it heats so quickly (being near the hottest part of the engine), the oil will get to the hot number fairly fast. Hence, 5w50... Fast flow, thick running.

skipc said:

Maybe it's the sender...

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The oil sender units on early model XJs have been reported as an item common to failure or inaccurate readings. It might be worth trying to replace it (they're pretty cheap) and see what readings you get. I have 5K on a rebuilt engine that is reading about 40 psi upon start up and around 25-30 when warm. The pressure seems to run higher when driving around town (shifting around 2K rpm) than on the open highway (cruising around 2K rpm).

desertred -- The oil sender units are about $40! I don't consider that cheap. Can you get it for less in Hermiston without watermelon as part of the trade?

Eagle said:

None of you guys who asked have any worries. The factory service manual (FSM) specs are (for a warm engine) 13 psi minimum at 650 RPM idle, 37 to 75 psi above 1600 RPM.

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I thought I'd throw in my two cents of problems. I had a long block 4.0 put in my 87 Jeep about a year ago and my pressure started going way down back in January (as in it bottomed out at idle on occasion). I switched to Mobil 1 and it got a little better. The dealership said it was the sending unit and replaced it - but it's still reading exactly the same. I get about 13 psi at idle and 20-25 at around 2000 RPM. Idle is okay but I'm not happy with the highway driving pressure. It's still under warrenty, but how can I convince the dealership that there's still a problem?

That's EXACTLY the pressures I was getting with 5w30 and 10w40, and only a little bit better with 5w50 now.

I've heard the senders can be bad even new. I'm toying with getting an external, diagnostic only, oil pressure gauge. NAPA has a nice one - 3" face, easy to use hose, etc for .... $60!!!

I dont' know which is worse, spending $60 to test a $12 part, or collecting $12 parts until one reads what I want it to :confused1 :

sjx40250 said:

desertred -- The oil sender units are about $40! I don't consider that cheap. Can you get it for less in Hermiston without watermelon as part of the trade?

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Whoops! You're right. Checking the web sites, the price is around $32. I was confusing the price for the oil pressure light switch that is available. Thanks for the suggestion, I may have to try the watermelon idea.