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Old 05-05-2013, 01:40 AM   #1
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oil pump bad?

I have an 02 4.0L with the typical fluctuation of oil pressure.
I have already changed the oil pressure sender(mopar oem) the readings are fine when driving and also when I stop at lights. The only time when the check gauges light comes on is when I turn off ignition, go into a store return and start it up. Once I rev it up to get the light off it's all good until I turn it off again.

Is it possibly the oil pump. I'm running 10/30 gastrol oil and Mopar filter.

Thanks
Ken

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Old 05-05-2013, 07:57 PM   #2
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Bump, any thoughts

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Old 05-05-2013, 08:25 PM   #3
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Not if the oil pressure is fine the rest of the time.

Sounds like the oil filter may be leaking down, resulting in a slow build up of oil pressure on start up.

How many miles on it?
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Old 05-06-2013, 12:13 PM   #4
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if it worked on the way to the store, i would think the pump would work once you started it back up again.

did you notice any difference what-so-ever after replacing the sending unit?
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Old 05-06-2013, 02:09 PM   #5
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Not if the oil pressure is fine the rest of the time.

Sounds like the oil filter may be leaking down, resulting in a slow build up of oil pressure on start up.

How many miles on it?
96 K

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Originally Posted by jherrington View Post
if it worked on the way to the store, i would think the pump would work once you started it back up again.

did you notice any difference what-so-ever after replacing the sending unit?
No change as it did the same thing before I changed the sender.
It only happens on restart when it's at operating temp. Once I rev it and get the gauge to go off it will be good even stopping at long traffic lights.

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Old 05-06-2013, 03:33 PM   #6
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I'd try a new filter first, cheap and easy.
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Old 05-07-2013, 12:59 AM   #7
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I'd try a new filter first, cheap and easy.
Did that twice,different oil and filter no change

Thanks
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Old 05-07-2013, 02:43 AM   #8
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Did that twice,different oil and filter no change

Thanks
Filter with back flow preventer?
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Old 05-07-2013, 02:27 PM   #9
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Filter with back flow preventer?
Good thought. I don't have any esperience with those, any brand i should try.

Thanks
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Old 05-07-2013, 02:52 PM   #10
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Good thought. I don't have any esperience with those, any brand i should try.

Thanks
I wouldn't be the guy to ask. I use a Bosch extra capacity filter and I think it's got one. Napa gold might.
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Old 05-07-2013, 03:21 PM   #11
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The Mopar filter has the anti drainback valve. You should be able to see the rubber through the small holes in the top of the filter.

The computer looks for oil pressure to be within a certain range within a certain time.

Yours is slow coming up for some reason.

You may have to get a mechanical test gauge to see what is going on.
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Old 05-07-2013, 03:33 PM   #12
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Pick up an inexpensive mechanical oil pressure gauge, remove your new pressure switch and plumb it into that port. Drive around for awhile and repeat the conditions where you experienced the low reading on your dash gauge.This way you'll know if you actually do have a problem. Autozone has cheap gauges for around $20 bucks.
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Old 05-08-2013, 12:10 AM   #13
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Pick up an inexpensive mechanical oil pressure gauge, remove your new pressure switch and plumb it into that port. Drive around for awhile and repeat the conditions where you experienced the low reading on your dash gauge.This way you'll know if you actually do have a problem. Autozone has cheap gauges for around $20 bucks.
Good idea, I think that's my next step

Thanks
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Old 05-16-2013, 01:20 AM   #14
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Pick up an inexpensive mechanical oil pressure gauge, remove your new pressure switch and plumb it into that port. Drive around for awhile and repeat the conditions where you experienced the low reading on your dash gauge.This way you'll know if you actually do have a problem. Autozone has cheap gauges for around $20 bucks.
Well I installed a mechanical oil pressure gauge and on a cold start up pressure is @ 50 then drops to 40 then when driving it's about 20 then after driving for awhile at idle it drops to about 3-5psi.
I don't hear any knocking or anything unusual motor sounds really tight.
What's the next thing to check

Thanks
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Old 05-16-2013, 08:34 AM   #15
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Umm, 3-5psi isn't high enough in my opinion. Anyone know if the 4.0 I6's oil pump has a high pressure relief spring in it like other makes of engine? Sounds like that spring is going out. That or there is a leak in the block somewhere, but that's exceedingly rare because it would mean a crack in an oil passage, and it should be far more noticeable even when the engine/oil is cold.

I'd replace that oil pump.
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Old 05-16-2013, 08:44 AM   #16
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Put some Good Mobile 1 10w30 Synthetic oil in it and see what happens. You've either got oil breaking down due to heat or the cam bearings are excessively worn.
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Old 05-16-2013, 03:06 PM   #17
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An oil change won't help him.


Don't you mean crank bearings?
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Old 05-17-2013, 12:39 AM   #18
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Put some Good Mobile 1 10w30 Synthetic oil in it and see what happens. You've either got oil breaking down due to heat or the cam bearings are excessively worn.
I've done 3-oil changes with different filters and presently has Mopar filter and castrol 10/30


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An oil change won't help him.

Yea I'm done changing the oil.
Bearings? I only have 95k on it and motor sounds great even with low to 0 pressure.
Whats next?












Don't you mean crank bearings?
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Old 05-17-2013, 01:22 AM   #19
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Quote:
Originally Posted by jherrington View Post
An oil change won't help him.
Don't you mean crank bearings?
^^^ This... My guess is also worn bearings. IMO your options are rebuild your motor, replace the motor or you might buy some time by replacing your oil pump with a high volume pump. If it were me I would try replacing the pump first since the motor isn't knocking. Pump, pan gasket, rear main seal, anaerobic sealer, RTV and High Tack. The RMS is not manditory but if the pan is off why not. Altogether should cost you about $150.00. Replacing the pump is not as complicated as it may sound, if you have basic mechanical ability you can do it yourself no problem. Can't paste links on my phone but check out DailyDrivenTJ.com - Welcome for a decent write up on the RMS, this will show everything except removing the pump which is simply 2 additional bolts and a little clearancing of the oil pan for the high volume pump.
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Old 05-17-2013, 06:10 AM   #20
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Quote:
Originally Posted by Wheats View Post

Well I installed a mechanical oil pressure gauge and on a cold start up pressure is @ 50 then drops to 40 then when driving it's about 20 then after driving for awhile at idle it drops to about 3-5psi.
I don't hear any knocking or anything unusual motor sounds really tight.
What's the next thing to check

Thanks
Had this same issue with my son's '00 4.0. Ran great, no knocks or rattles, just low op when warm. I figured it probably had worn crankshaft main bearings.
Quote:
Originally Posted by scot68 View Post

^^^ This... My guess is also worn bearings. IMO your options are rebuild your motor, replace the motor or you might buy some time by replacing your oil pump with a high volume pump. If it were me I would try replacing the pump first since the motor isn't knocking. Pump, pan gasket, rear main seal, anaerobic sealer, RTV and High Tack. The RMS is not manditory but if the pan is off why not. Altogether should cost you about $150.00. Replacing the pump is not as complicated as it may sound, if you have basic mechanical ability you can do it yourself no problem. Can't paste links on my phone but check out DailyDrivenTJ.com - Welcome for a decent write up on the RMS, this will show everything except removing the pump which is simply 2 additional bolts and a little clearancing of the oil pan for the high volume pump.
^^ This is exactly what I did. Purchased a Melling high volume oil pump and installed it. Pretty straight forward job. The hardest part for me was getting the exhaust loose at the manifold. I had to cut the bolts. I also had to install an aftermarket oil pan because the plug in the old one stripped out the threads. I did not have to modify the that oil pan at all but I don't know about the OEM pan. I couldn't imagine it would be more than modifying the internal baffle. It has been a year since the install and still running great. It starts up at 60psi, idles at 20-25psi warm, and highway cruises at 50-55.
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Old 05-17-2013, 11:17 PM   #21
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Had this same issue with my son's '00 4.0. Ran great, no knocks or rattles, just low op when warm. I figured it probably had worn crankshaft main bearings.

^^ This is exactly what I did. Purchased a Melling high volume oil pump and installed it. Pretty straight forward job. The hardest part for me was getting the exhaust loose at the manifold. I had to cut the bolts. I also had to install an aftermarket oil pan because the plug in the old one stripped out the threads. I did not have to modify the that oil pan at all but I don't know about the OEM pan. I couldn't imagine it would be more than modifying the internal baffle. It has been a year since the install and still running great. It starts up at 60psi, idles at 20-25psi warm, and highway cruises at 50-55.
Thanks. As soon as I get time that's next on my list
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Old 05-19-2013, 07:34 PM   #22
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Originally Posted by All Terrain TJ View Post

Had this same issue with my son's '00 4.0. Ran great, no knocks or rattles, just low op when warm. I figured it probably had worn crankshaft main bearings.

^^ This is exactly what I did. Purchased a Melling high volume oil pump and installed it. Pretty straight forward job. The hardest part for me was getting the exhaust loose at the manifold. I had to cut the bolts. I also had to install an aftermarket oil pan because the plug in the old one stripped out the threads. I did not have to modify the that oil pan at all but I don't know about the OEM pan. I couldn't imagine it would be more than modifying the internal baffle. It has been a year since the install and still running great. It starts up at 60psi, idles at 20-25psi warm, and highway cruises at 50-55.
Did you adjust the pressure relief valve any?
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Old 05-19-2013, 08:54 PM   #23
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Did you adjust the pressure relief valve any?
I did not.
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Old 06-23-2013, 10:24 PM   #24
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Had this same issue with my son's '00 4.0. Ran great, no knocks or rattles, just low op when warm. I figured it probably had worn crankshaft main bearings.

^^ This is exactly what I did. Purchased a Melling high volume oil pump and installed it. Pretty straight forward job. The hardest part for me was getting the exhaust loose at the manifold. I had to cut the bolts. I also had to install an aftermarket oil pan because the plug in the old one stripped out the threads. I did not have to modify the that oil pan at all but I don't know about the OEM pan. I couldn't imagine it would be more than modifying the internal baffle. It has been a year since the install and still running great. It starts up at 60psi, idles at 20-25psi warm, and highway cruises at 50-55.
Well I installed a high volume oil pump although it's better it still drops to zero and check gauge light comes on after driving for awhile(no ticks or knocks). At this point I'm just going to drive it and deal with it down the road.

Thanks for all replies
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Old 06-23-2013, 11:42 PM   #25
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Well I installed a high volume oil pump although it's better it still drops to zero and check gauge light comes on after driving for awhile(no ticks or knocks). At this point I'm just going to drive it and deal with it down the road.

Thanks for all replies
Sorry to hear about that.. If you plan on rebuilding, I would do it as soon as you get the funds/time. Letting your engine wear too much in the state that its end could make it too worn to rebuild
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Old 06-25-2013, 05:33 PM   #26
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Sorry to hear about that.. If you plan on rebuilding, I would do it as soon as you get the funds/time. Letting your engine wear too much in the state that its end could make it too worn to rebuild
Any idea on cost and whats involved if I do it now vs if I wait.

My daughters are home from college and of course are driving the jeep so it will have to wait until end of July

Thanks

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