low oil pressure to new engine? - Page 2 - JeepForum.com
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post #16 of 59 Old 03-20-2015, 03:41 PM Thread Starter
bergovoy
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yea, I could buy one, but, I don't want to bypass my electric gauge... i would need a TEE, or something, and I probably couldnt do this as my backis kinda limited...and there is too much stuff in the way...for me...

probably take a shop an hour or so to install one for me.???

i was just thinking of getting it 'tested' with a mechanical gauge... and not have an oil line running into my cab

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post #17 of 59 Old 03-20-2015, 04:25 PM
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Ah! I see what you were intending now. Sorry about that, I thought you were having a hard time finding one to install. Don't blame you on not wanting a pressurized oil line running into your cab, it does add a potential for a mess that wouldn't ordinarily be there.

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post #18 of 59 Old 03-20-2015, 05:58 PM Thread Starter
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ah, I see said the blind man to his deaf dog....

hehe

anyways here are some pics...


they were taking just a short bit ago...and taken over the course of 30 minutes(ish) all at idle.... I did drive the jeep but took pictures at each of my stops...and then when i got back home.

it shows normal, maybe even HIGH oil pressure when i start the jeep.. then as the temperature starts to rise the oil pressure starts to drop.. until it gets to just a tad above zero.

Im sure that if I drove it a little longer it would get a bit warmer and the pressure gauge would be zero.



the pressure does go up when I raise the rpms... but when the pressure gets down, the only increase is nominal.. never to the first tic...
Attached Thumbnails
oil pressure normal - cold temperature.jpg   oil pressure starting to drop - temperature starting to get warm.jpg   oil pressure dropping more - temperature getting almost normal.jpg   oil pressure dropping faster - temperature getting near normal.jpg   oil pressure almost zero - temperature normal.jpg  

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post #19 of 59 Old 03-20-2015, 10:05 PM
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Ya. The oil pressure does look good and then falls off. Something is up and it's not your bottom end...

1989 YJ- Dad original owner given to me in 1997.
2001 XJ- Wifes and currently under construction
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post #20 of 59 Old 03-20-2015, 10:58 PM
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Low oil pressure:

Bad sender/ gauge
Fuel contaminated oil (thinned out)
Worn oil pump
Excessive clearance main bearings, rod bearings, cam bearings, all or some or one.
Plugged pick up tube. (screen has safety valve)
Bad filter (Doubtfull, they also have a bypass)
Motor too hot

Take your pick.
After seeing the picks, I still believe it's most likely cam bearings (mostly)

The oil pressure is good till the engine oil warms then the oil thins. The thinner oil leaks past the cam bearings and crank bearings.
The path from the oil pump is: filter, then cam, then some goes up to the lifters and valve train and some goes down to the crank and pressure is measured at the rear of the crank.
This is from my somewhat cloudy memory so correct me if I'm wrong.

Again, I would do nothing drastic till all diagnostics are followed.

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post #21 of 59 Old 03-20-2015, 11:00 PM
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Definitely scary to see it that low! Mine was doing almost that exact same thing, but at idle it would stay just a hair higher than that last pic. Still below the first tic mark though. And then when I gave it throttle, it would climb to visit around 25ish.

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post #22 of 59 Old 03-21-2015, 08:17 AM
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Quote:
Originally Posted by Chrisnvegas View Post
Low oil pressure:

Bad sender/ gauge
Fuel contaminated oil (thinned out)
Worn oil pump
Excessive clearance main bearings, rod bearings, cam bearings, all or some or one.
Plugged pick up tube. (screen has safety valve)
Bad filter (Doubtfull, they also have a bypass)
Motor too hot

Take your pick.
After seeing the picks, I still believe it's most likely cam bearings (mostly)

The oil pressure is good till the engine oil warms then the oil thins. The thinner oil leaks past the cam bearings and crank bearings.
The path from the oil pump is: filter, then cam, then some goes up to the lifters and valve train and some goes down to the crank and pressure is measured at the rear of the crank.
This is from my somewhat cloudy memory so correct me if I'm wrong.

Again, I would do nothing drastic till all diagnostics are followed.
This is something I hadn't thought of yet, thank you for pointing us in that direction! I did some searching online, and so far I've found 2 articles that seem to be saying that it is 1) filter, 2) crankshaft, 3) cam and valve train, 4) gravity drop back to the pan to circulate again.

http://www.machinerylubrication.com/...in-your-engine

http://www.auto-repair-help.com/auto...ion_basics.php

With that being said: What type of diagnostics do you think might point to a good starting place? Seems like the 3 most likely culprits to our problem here are going to be either the pump, the cam bearings, or the crank bearings. Any thoughts on narrowing it down to one of the 3?

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post #23 of 59 Old 03-21-2015, 08:53 AM
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Every motor is different. Here is a diagram I found for the AMC 258. It's the lubrication circuit.
The oil goes from the filter to the main oil gallery... look at the arrows.

Expand the pic:



I would consider myself an (maybe slightly above average) amateur garage mechanic. Therefore I suggest consulting with someone more knowledgeable than me before tearing into a potentially expensive job like this.
I would verify condition of oil and filter
Verify oil pressure numbers with an accurate mechanical gauge. Not a crappy chinese gauge either. Still low?
Pull the pan. Check pickup screen. OK? Then get specs for the oil pump and determine wear. OK? then check wear to main bearings (Plasticgauge)

That would probably be a good starting point.

Here is a pdf 258 engine manual. Save it in your computer so you can print pages you need.

http://theamcforum.com/forum/uploads...ine_Manual.pdf

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post #24 of 59 Old 03-21-2015, 09:15 AM
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Thank you! Is that pic from the FSM? I hadn't come across that page yet, I'll keep digging there. Not sure how much of that the OP has already done, but I've done quite a bit of it already on mine. Fresh full synth oil and Lucas, with a new Wix filter, I will admit that my mechanical gauge is a cheap crappy one, lol! But the readings it's giving are identical to what the factory gauge was showing, so I'm gonna say it's accurate. Guess it's time to pull the pan & start getting dirty!

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post #25 of 59 Old 03-21-2015, 09:23 AM
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It is from the FSM.

I'm sticking with my prediction. Cam bearings. I ended up replacing the cam, bearings, lifters, pushrods, rockers ect.
Left the mains alone. This raised the pressure to @ 18 or so hot idle and @ mid 30's driving hot. Perfectly acceptable. Lasted me from my early 20's to my mid 30's (Then I got married and sold it for a Subaru )
I did the work without removing the motor. Took about a week (I still had to work) and was a good excuse for a beefier cam. Then I got a small Holley 4 barrel. Really woke the old 4.2 up.

But now I'm back!

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post #26 of 59 Old 03-21-2015, 03:04 PM
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I strongly suspect the bearings, they actually determine most of the oil pressure especially while idling hot. I would replace the rods mains *and* cam bearings. Like Chrisnvegas said, the job can be done without pulling the engine. In fact, I'm looking at a similar situation in about 10K miles, my pressure has been slowly dropping at 190K miles right now...

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post #27 of 59 Old 03-21-2015, 04:07 PM Thread Starter
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Quote:
Originally Posted by mickcollinsb16b View Post
Ya. The oil pressure does look good and then falls off. Something is up and it's not your bottom end...
Quote:
Originally Posted by Chrisnvegas View Post
Low oil pressure:


After seeing the picks, I still believe it's most likely cam bearings (mostly)
can you all elaborate as to why you are suspecting the cams, and not the mains?

and yea, i will try to get prices on replacing just the cams, and then just the mains...

thanks
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post #28 of 59 Old 03-21-2015, 05:28 PM
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Quote:
Originally Posted by bergovoy View Post
can you all elaborate as to why you are suspecting the cams, and not the mains?

and yea, i will try to get prices on replacing just the cams, and then just the mains...

thanks
If it was just the mains, etc. then you would maybe get a lot more knocking and tapping especially under heavy acceleration. Since you don't seem to have that, that only leaves the cam bearings as a possibility. Thing is tho, I think it is best practice to simply replace all bearings at the same time, (rods, mains, and cam) shopping around can get you the whole set for under $200 I bet.

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post #29 of 59 Old 03-21-2015, 06:08 PM
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Guys are making this harder the it needs. Take the oil pressure sender out 1/8 NPT and install a mechanical gage for a test purpose.


Take the readings.


From the OP`s description of his health the he is not going to do it himself. Engine most likely comes out and ALL the bearings replaced.


It`s a no brainer...........Low oil pressure worn dfead engine. what does it matter if it`s cam or main.
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post #30 of 59 Old 03-21-2015, 06:53 PM
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Quote:
Originally Posted by jsawduste View Post

From the OP`s description of his health the he is not going to do it himself. Engine most likely comes out and ALL the bearings replaced.


It`s a no brainer...........Low oil pressure worn dfead engine. what does it matter if it`s cam or main.
Pretty much what I've been trying to say. Bearings are cheap, if you are doing one then you might as well do them all. As I said, IMHO its best practice to do them all at once.

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