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Unread 07-29-2010, 07:50 PM   #1
Sundowner
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Mystery Oil Pressure Loss

Talked to a friend tonight that's experiencing a loss of oil pressure...he's driving a 1997 with a 2.5 and about 120K miles on the clock. In his words, "After it warms up, the oil pressure falls when I'm sitting at a stoplight. The gauge just creeps down to zero." Now, I stood in the driveway and watched this happen...if he lets out the clutch just a bit, the needle starts heading left. Evidently, it doesn't do this when it's cold, and running 15w30 helps "a little bit." It's been doing this for a couple of years, it seems, and he's replaced the oil pressure sensor, and the oil pump as well. There's absolutely no sign that the engine is unhappy at all...I stood there and listened to it...purrs along like a 2.5 liter kitten. No noises, clicks, taps...nothing...even the valvetrain is quiet. He mentioned that the only thing he knew that might be "wrong" with the engine at all was a vacuum leak that he could hear, "sometimes, when it's hot."

I don't have any ideas on what's the matter...I don't know the 2.5, and I don't know a lot about the oiling system or its sensors. Professional help needed.

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Unread 07-29-2010, 08:10 PM   #2
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Put a mechanical gauge on it to check the true pressure first.
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Unread 07-29-2010, 08:13 PM   #3
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That was sort of where I got left, as well...wondering if the gauge just wasn't telling us what we need to know. A mechanic he took it to told him that he needed a new engine. I'm not kidding about that.
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Unread 07-29-2010, 08:24 PM   #4
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The same thing has been going on with my 01 TJ w/ V6. Its been going on for a while too, just haven't found the time to fix it yet. I was told that a new oil pressure sensor would fix it.

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Unread 07-29-2010, 08:27 PM   #5
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Well, the Jeep in question already has a new sensor in it (so I'm told) so that possibly eliminates that source. It's just strange that it's such a repetitive condition.

Oh, and you don't have a V6, unless you swapped one in.
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Unread 07-29-2010, 08:55 PM   #6
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Thicker not thinner

Since I completed my build last year, I've noticed during the "jungle hot" summers of South Mississippi that when the motor is warm and I shut it down, say while I'm filling up with gas, that when I start it up again, my pressure takes about 3-5 seconds to return. A perfect example of my delimma is when you change the oil and you start it the first time, it takes a few seconds to get pressure. Anyway, I asked my machinist his take and he told me to either run Valvoline VR1 (SAE 60) or add some really thick stuff from Comp Cams. Somehow, 45 mins later when I left his shop, I didn't have the goo. Since I had already bought some Castrol GTX 10W-40, I decided to add some Lucas oil treatment.
Results: not completely known since I just changed the oil tonight and have not yet experienced the heat of the day with a hot motor. I can tell you that the pressure is higher than it normally is so thicker must be better.
So, add a quart of some good thick stuff like the Lucas and see if that makes a difference. It can't hurt it.
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Unread 07-29-2010, 09:15 PM   #7
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Yes, I agree that adding a thick oil would help...but it would only help the symptom. It does nothing to actually address the problem. It's the same as saying that taking aspirin "fixes" a headache...there's still a causative factor for the headache, but you just can't feel it at the time.
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Unread 07-29-2010, 10:02 PM   #8
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Without screwing a mechanical guage in it your friend will never know what is really going on. It could be anything from worn out cam bearings, crank bearings, bad oil pump....etc.
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Unread 07-29-2010, 10:02 PM   #9
George Dickel
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Great analogy on the aspirin thing. He probably has a problem, I had an issue. The main point here though is that the thick stuff will linger longer up top thus hopefully helping avoid cam lobe destruction or some other major problem until he finds the culprit.

If I'm him, I wouldn't let this go on for 2 years. With that said, and the fact that he's changed the sensor, I'd drop the pan and take a good look at the screen on the oil pump inlet. If that's free of debris/gunk, I'd change the oil pump.
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Unread 07-30-2010, 06:47 AM   #10
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Yeah, I was kind of surprised to hear about the 24-month time frame as well...but it seemed to be a "well, it still runs fine" kind of thing. Ugh...

If I recall correctly, he's also changed the oil pump, and I think he's adding Lucas to the mix already. So we're covered there. Looks like a mechanical gauge is in the works. Oh well...excuse to buy tools.
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Unread 07-30-2010, 08:09 AM   #11
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Quote:
Originally Posted by Sundowner View Post
Looks like a mechanical gauge is in the works.
Where can you buy a mechanical gauge to check this? Any parts store?
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Unread 07-30-2010, 08:21 AM   #12
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I've found several online this morning. Anywhere from $40 to $180...I have no idea which ones are good and which ones aren't, so I'm going to have to look into it. Might just rent one from the parts store, if possible.
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Unread 07-30-2010, 08:46 AM   #13
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My Jeep has done this since at least 06. 4.0 Oil pressure is fine until it warms up. If I am at an idle it will drop down to 0 and the check gauages light will come on. As soon as I give it some gas it comes back up again. I wish it would blow so I can drop a 4bt in it.
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Unread 07-30-2010, 08:58 AM   #14
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Quote:
Originally Posted by MuddyJeepZJ View Post
I wish it would blow so I can drop a 4bt in it.
So there isn't a fix for it? I should just expect my engine to give out at some point?

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Unread 07-30-2010, 09:08 AM   #15
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Personally, I don't have a fix for it, because I still don't know what's wrong. I haven't ever wished for a part to break, though. If you want the 4BT, why not just put it in...
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