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Unread 01-20-2010, 06:30 PM   #1
Black1993
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Jeep 4.0 low oil pressure

hey guys this one is really killing me. I have a 1993 cherokee 4.0 and when the engine gets hot the oil pressure drops to about 4-5 psi. i replaced the sensor and just incase i have installed a mechanical gauge inside the jeep for a failsafe. Also when the temp goes up and the pressure goes down the jeep will start to blow blue smoke out the tailpipe. i was going to the autoparts store to buy a new oil pump because i dont know what else to do. oh yeah when the pressure drops, i drive it and the pressure only goes up to about 25-30 psi. HELP!

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Unread 01-21-2010, 06:05 AM   #2
tjwalker
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So the mechanical oil pressure gauge confirms that the pressure is 4-5 psi? How many miles on this engine??

If that is the case, you've got engine problems. Excessive clearances either in the bearings, oil pump or both would be likely.

You may want to try to isolate this a bit and drop the oil pan to check your bearings before buying parts.
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Unread 01-21-2010, 04:09 PM   #3
slimpartywagon
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Is the blue smoke on start up, or the whole time you are driving? if its on start up you have bad Valve Seals, if it is continuous then you have bad rings. Bad rings would also go with your low pressures. I would do compression test to confirm combustion chamber problems. Then if nothing is suspect i would get a new oil pump and carefully inspect the lower part of the engine block for problems while the pan is down.
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Unread 01-21-2010, 04:56 PM   #4
Black1993
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the jeep has 164k and the gauge reads 4-5 psi at HOT idle. 1989 xj cherokee: the jeep doesnt smoke on start up, it just smoke when its idling for a while when the engines hot. Idk if this helps but when i got it i ran seafoam through it, i never really noticed before if the pressure was low. It could have been, it could not have been, idk. but when i ran that throgh the pressure, i noticed was low. i figured that the seafoam might have lossened junk inside and was clogging the screen. so what i did was dranied about a quart and a half of oil and added auto trans fluid to it, let it run for a while and changed the oil. and that seemed to fix it i was running 60-65 psi driving wit the engine hot. and 40 psi at idle. but after a while the pressure droped and now its at the current state. i need all the help i can get. Thanks guys
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Unread 01-21-2010, 05:12 PM   #5
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Quote:
Originally Posted by Black1993 View Post
the jeep has 164k and the gauge reads 4-5 psi at HOT idle. 1989 xj cherokee: the jeep doesnt smoke on start up, it just smoke when its idling for a while when the engines hot. Idk if this helps but when i got it i ran seafoam through it, i never really noticed before if the pressure was low. It could have been, it could not have been, idk. but when i ran that throgh the pressure, i noticed was low. i figured that the seafoam might have lossened junk inside and was clogging the screen. so what i did was dranied about a quart and a half of oil and added auto trans fluid to it, let it run for a while and changed the oil. and that seemed to fix it i was running 60-65 psi driving wit the engine hot. and 40 psi at idle. but after a while the pressure droped and now its at the current state. i need all the help i can get. Thanks guys
try to avoid putting further stuff in the crankcase.

by carefully reading your post, i'd suggest a drain and fill with higher viscosity oil immediately depending on if your motor uses oil. if it's a quart every 200-500 miles and you smoke once warmed up, it could be a large variety of things. Do you get good gas mileage? are the plugs nice and clean?

a few things first, but if its' within your realm i'd try a complete oil drain and fill, new filter, with 20w-50 and see where that gets you.

after that, a new oil pump would help. there's quite a few tips on the forum regarding oil pumps, the main issue to remember is to seal it all properly. and if you're doing that...bite the bullet and change the rear main oil seal, and check bearings out while you're in the there.

you stated that for a while you had good oil pressure (60 psi hot, 40 psi idling) but i'd go with mechanical pressure gauge as i've put 2 pressure senders in mine as they do wear out and either show really high pressure or way low....which makes me nervous and not really trusting of the stock pressure sending unit.
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Unread 01-21-2010, 05:18 PM   #6
webdog
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Yes try a thicker oil, I have been running 20W50 to help with a low oil pressure.
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Unread 01-21-2010, 06:36 PM   #7
Black1993
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So should i just change the oil and filter, but put a pump in also? or just try the oil first. And i heard that the ATF works because it gets rid of sludge and swells the seals, just good for the motor, but idk bout that either.
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Unread 01-21-2010, 07:29 PM   #8
Black1993
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also wont 20w50 hurt the motor in cold starting, where i live it gets down to the negatives!
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Unread 01-21-2010, 07:46 PM   #9
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To help with cold start ups I'd throw in a Quart of Lucas oil Stabilizer and agree with either 15-40 or 20-50
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Unread 01-22-2010, 04:17 PM   #10
slimpartywagon
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since you are having piston ring blow by... I would not put any atf in it... I would also be looking into a rering kit, or an overhaul kit and rebuild the engine soon...
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Unread 01-22-2010, 05:14 PM   #11
koolaid5
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I had a similar problem recently minus the blue smoke. I noticed the low oil pressure after running sea foam in the HEEP shortly after buying it. I THINK I just broke some gunk loose and either ruined or just clogged the oil pump, so I replaced the oil pump, scree, and pick-up tube with a high volume one and all is well. I tried replacing the OP sender like you did and the thicker oil first (20w50), but neither changed a thing. The oil pump did the trick though.
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Unread 01-22-2010, 08:52 PM   #12
Black1993
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Thanks everyone for the help.. i put the thicker oil in tonight and the pressure seems great. 25 psi at hot idle, and 45-50 driving..but its new oil so anything can happen. I also threw in some stuff that says stops smoke so we will see how that does, if not i guess its the oil pump next..
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Unread 01-22-2010, 09:19 PM   #13
koolaid5
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good deal.....glad to hear that. Did you happen to change the filter as well? I've read over and over on here that some have had those symptoms just from using a FRAM oil filter.
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Unread 01-22-2010, 09:37 PM   #14
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In the future, you really ought to avoid that stop smoke and other additives. Lucas Oil Stabilizer is, as far as I'm concerned, the only thing you should add to your oil. But, so you know, when that blue smoke comes out after it's warmed up and what not, it's because oil is leaking into the combustion chamber(s) somehow. If thicker oil solved your problems for now, it probably will for a long time. However, if it does do it again, it's probably not your oil pump unless you've got some REAL bad oil. IF it does it again start with a compression check, in fact, I probably wpuld do it anyway. Compression test gauges are cheap and very simple. Disconnect the distributor and take the plugs out. Then put the connector into one hole at a time and turn it over for a sec. A manual will tell you the acceptable compression. If any are below it, like the guy farther up said, start saving for a re-ring kit.

and Koolaid...really? I've always used Fram toughguards. What would you suggest? /end hijack
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Unread 01-22-2010, 11:01 PM   #15
slimpartywagon
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I agree with Towmaster, if you still have smoke... its not your oil pump oil pump only affects your pressure... if your oil pressure is good, but you are still smoking... then you have internal engine problems... and by what you describe... i give it a 80% chance of worn piston rings, 5% chance of scored cylinder walls, 10% chance of both, and 5% chance of piston wear... I still recommend getting a head gasket set and pulling your head to check the condition of your cylinders, pistons, and rings (after a compression test just to make sure you are loosing compression). While the head is off, I would have it checked out by a machine shop for bad valve train parts.
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