Oil pressure needle goes up, then down

My oil pressure goes up when I accelerate, then down when I stop. It goes up to 70 when I hit the gas and down to 20 when i'm stopped. Could it be oil pump?

HaZakated said:

Could it be oil pump?

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I'm certain that it is...


...working properly.

Sounds fine to me. Rev the engine, pressure goes up. Idle the engine, pressure goes down. Mine does the same thing.

Im still a noobie but that seams like a big jump to me. Not to question a member with over 1500 post under their belt. Im probably wrong... just seems like a big jump.

Yeah, 70 sounds a bit high to me, even when the oil is cold. 20 at a hot idle is alright. It's possible that the sending unit is starting to flake out...

It is a bigger than normal difference, which may indicate that your oil pressure sending unit is defective, but in general the behavior is correct. The factory service manual (FSM) specifies oil pressure as 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. You are within spec, so I suggest you consider it a GO / NO-GO instrument and not panic until it starts doing something different.

Eagle said:

You are within spec, so I suggest you consider it a GO / NO-GO instrument and not panic until it starts doing something different.

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Yep. Had the exact same behviour on my 2001 around the time that the pressure sending unit started to go. Once it got really bad, it would hit zero and the 'CHECK GAUGES' light would illuminate. First time it happened I was going 75mph, so after an initial oh-holy-crap moment, rationalised the situation and realised that if the oil pressure really were at nil I'd probably know about it without having to resort to the gauge.

FWIW, both my 2000 and 2001 idle warm at 20psi, and hit 50-55psi under running conditions. 70 sounds a bit high to me, too, though, but still within spec. Apart from the sending unit, have you checked the oil level lately? Over or underfill can have different effects on what the gauges report as well. The rise and drop you're seeing under rest and acceleration is normal, though.

I've always been told and taught and/or found out that most all of the factory's generally have a rule-of-thumb of somewhere around 10-15psi per 1000 rpm's as a minimum. As for a maximum...usually they say nothing until it reaches upwards of 80psi ..... or more even...sometimes.
Aron

An oil pressure of 10psi per 1000rpm is the rod rodders rule of thumb, but that doesn't necessarily apply to street engines.
As Eagle said, minimum oil pressure at idle should be 13psi and above 1600rpm it should be 37psi when the oil's hot. The oil pressure will, of course, be higher when the oil's cold because at low temperatures the oil thickens.
HaZakated, your engine's oil pressures are fine; 70psi when you hit the gas is definitely high (even though it's just within spec) and probably indicates a faulty sending unit. I wouldn't fret about it though. I'd only worry if the oil pressure reading is too low.

I was just saying that as a "general rule" 10-15 psi at 1000 rpm or less(idle) is ACCEPTABLE...within their minimums. I personally don't like my motors...street or strip...to carry that low of an oil pressure. GM is one of the main manufacturers that claims 10-15psi for 1000 rpm minimum...and up to 10 psi per 1k rpm thereafter and up to 60psi. But from what I've been told Jeep/Chrysler says very close to the same...that 10-15 psi at 1000 rpm or less(idle) is acceptable.....within their MINIMUMS..... and up to 60psi or a little bit more is acceptable on the high end with them too.

I've seen factory gauges be off by as much as 15 to 18 psi before as well...so I wouldn't worry too much...but if I was worrying I might get a quality, mechanical, name brand gauge to double check it with or replace it.

Most manufacturers mainly say that the psi should rise rather QUICKLY as the gas is applied.
Aron

What is strange about this, is that I just noticed that it was rising and falling this weekend and I've had my 2000 XJ since 2001. I thought there was a problem for sure, but It could very well have been that I simply didn't notice it the whole time. Thanks for the help! I just changed the oil last week after sinking my Jeep, but i'll check the fluid level just to make sure I filled it correctly. I always put the same amount in each time, 5.75 qts of 10W-30.
Brian

I just took a 700+ mile trip in my '91 through the mountains last week and had plenty of time to watch the guages.

Mine acts the same way...20 at idle - 70 at take off - 40 at cruising speed. It's been doing this as long as I've had it and has never given me any problems.

BigDawgz said:

But from what I've been told Jeep/Chrysler says very close to the same...that 10-15 psi at 1000 rpm or less(idle) is acceptable.....within their MINIMUMS..... and up to 60psi or a little bit more is acceptable on the high end with them too.

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You were told wrong.

I quoted the Jeep specs above. 13 psi minimum at idle, 37 to 75 psi above 1600 RPM. That's what the Jeep FSMs have said all the way from 1988 through 2001, and that's what the AMC FSMs said for the older versions of the same engine family as far back as 1964.

Why repeat hearsay when the correct information has already been posted?

HaZakated said:

I always put the same amount in each time, 5.75 qts of 10W-30.

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Just out of curiosity, why don't you put in 6 quarts, as called for?

Sounds like the sending unit to me. My girlfriends dakota has the same symptoms and its a sending unit gone wonky.

Eagle said:

Why repeat hearsay when the correct information has already been posted?

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Not arguing...just thought I'd explain myself a little better.

The "supposed" hearsay was from 3 different Jeep/Chrysler techs.....2 of which have been Jeep/Chrysler techs for 27 years....between them. These guys are at Chrysler's "Gold Level"...that...combined with being a Master Technician...is the highest level that you can achieve. Their dealership is a 5-star dealership as well.

That's not really hearsay. That's coming straight from the guys who perform the work and sit in on all the Chrysler tech training and update meetings and seminars and receive all the update bulleteins everyday. It's by the input of techs, like these guys, that Jeep/Chrysler can continue to change and update what is and what isn't acceptable for the servicing of their automobiles. One of these techs has been my best friend for close to 20 years.

I would trust someone that I've known and someone that has excelled in working on Jeeps/Chryslers for the past umpteen years....way more than I would trust the FSM. Real world experience counts in my book.

I'm not saying that the FSM's are wrong, necessarily...but they sure do continually change and update faulty material from within the FSM almost on a daily basis...at times. Besides....the techs that I personally know, take the FSM's with a grain of salt. These are some of the highest paid, well-rounded, knowledgeable techs around.

Not all dealerships have great techs....but some are lucky enough to have some excellent techs who's skills can be quite amazing.

I don't think there's anything wrong with posting a different opinion about what's being talked about or what has already been stated.....and especially not when it's coming from guys who work on what we're discussing every single day. Especially since these guys are Jeep/Chrysler Techs. I was simply passing on what they had said about it when we had discussed it in the past.
Aron

Eagle said:

Just out of curiosity, why don't you put in 6 quarts, as called for?

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I generally end up putting in about 5.75 quarts. The dip stick reads full (top of safe) with that amount of oil.

90Pioneer said:

I generally end up putting in about 5.75 quarts. The dip stick reads full (top of safe) with that amount of oil.

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Before or after starting the engine?

Don't forget the oil filter is empty after you change it. The specified capacity is 6 quarts, and I have yet to put in 6 quarts and have the dip stick read over-full.

I always put 5 qts in and run the engine for about 2 minutes. Then I add 3/4ths of a qt and it reads full. I then save up the extra .25 qts in a box in my garage and add them to future oil changes. I'm sure it doesn't matter. The maual doesn't apply to me much anymore....LOL. I change my transmission pan fluid every time I do a moter oil change. I change my transmission filter every 20,000 miles. I change my transfer case once a year as long as I dont sink my XJ. I change my differential fluid once a year (I always use friction reducer). I change my coolant once a year. The way I figure, this way I might add some extra miles to an XJ that is beaten and abused atleast once a month. I'm anal about waxing my jeep as well. I'll wax it, go offroad, wax it, go offroad. Iv'e had my XJ since 2001. It is my first one. I am extremely impressed with the engineering of it, and want to keep it going strong off, and on the road.
As far as the oil pressure issue. I appreciate all your help with this matter. I can now rest a little easier knowing that my engine will not sieze up going down the road due to lack of oil pressure. There are a great deal of intelligent people here at . I am thouroughly impressed with your willingness to help, and the knowlege that everyone brings to the forum.
I take much pride in the name JEEP. Without that name, I wouldn't be writing on this forum or even born for that matter. My grandfather was part af the Army Cavary in WW2. He recieved a Bronze Star, Purple heart, and many other medals for his willingness to go above and beyond the call of duty. He has told me stories of times where the JEEP got him out of many life threatening situations. He says in this perticular situation, "The Jeep was great because it was so quiet. You could literally drive right next to the enemy and they wouldn't notice that you were there. One time my unit was traveling with 3 JEEPS full of people. We were ambushed and my driver got shot in the head so grabed the wheel, ducked, and sped out of there. When I got back to base there were 3 tires shot out, the radiator had holes every where and I was the only person out of my whole unit (10 people) that survived."
There are no words that I can say, or quote that I can write, that could begin to describe the honor and commemoration that people like my grandfather and the engineers of the JEEP deserve. I tell you of this story today because I am free. I am free get my XJ dirty, and proud to shine my light, to raise my voice, and fly our flag of red...white...and blue....stars and stripes.

Brian M. Hayes

Thanks for the help!