jeep_freek88 Posted September 25, 2012 Share Posted September 25, 2012 I just bought a 1997 xj 4.0 auto and drove it 400 mi home. The guy I bought it from said he had just did an oil change and switched to synthetic 5w20... I know pretty light if you ask me even for winter, but whatever. On the drive home cruzin at 70mph I knoticed that the oil pressure seemed low reading between 30 and 40 at speed and dropping to like 15-20 at idle I was concered because in my MJ with the same engine it runs 50 at idle and 75 at speed when hot which I have never had any complaints about I run 10w30 blend in the MJ btw. I have had the xj for about three weeks and figured I would just do an oilchange and put in some 10w30 when the oil he had put in it was spent. Well now my oil pressure is like 5 psi at idle and maybe 10 when running down the road and I could smell oil cooking needless to say it is now parked untill I figure out what is wrong because I don't want to ruin the engine. I read somwhere on a post once that the pressure sending unit could cause faulse reading is there any way to tell if the sending unit is bad? I was also thinking about just putting a new high flow oilpump in because the rig has 161000mi on it so it couldn't hurt right? $80.00 bucks for the pump $30.00 for the sending unit what should I do any suggestions on how to figure out the problem, or advise on what you would do would be greatly appriciated i don't have alot of $$ thanks in advance. Us jeep freaks have to stick together! :help: p.s. I saw a mj parked at my work ill post a pic in the pub lol felt like a creap out in the parking lot at night taking a pic of someones mj :brows: :banana: Link to comment Share on other sites More sharing options...
jeep_freek88 Posted September 25, 2012 Author Share Posted September 25, 2012 Ok just went out and started it cold and at idle when cold it sits right at 40 and at 3,000 rpm it goes to 50, So idk maybe just need different oil in it?? when hot the pressure will drop drasticly Link to comment Share on other sites More sharing options...
Zenobian_84 Posted September 25, 2012 Share Posted September 25, 2012 Wouldn't hurt to swap in another gauge to test if the sender is bad. If the other one reads the same, change the sending unit first. Can't recall where it's located on the 4.0, but that's probably what I would do first. If the new OSU (oil sending unit) reads the same, then you should probably move on to swapping a new oil pump in. :thumbsup: Always start with the cheap stuff and work up from there. Link to comment Share on other sites More sharing options...
jeep_freek88 Posted September 25, 2012 Author Share Posted September 25, 2012 my thoughts were to replace the pump first then i would know that i have good pressure regardless of the reading then the sender later if need be, but now I'm thinking of just changing the oil, maybe putting in some seafoam then changng the oil would be cheaper than a sender or pump, but a gamble either way you look at it Link to comment Share on other sites More sharing options...
jimoshel Posted September 25, 2012 Share Posted September 25, 2012 Sounds like bearing s to me. When the engine gets warm the bearing clearance increases and the oil pump can't keep up. The very first thing I suggest you do is get a pressure gauge and check your current gauge, sender unit for accuracy. Two ways to check bearing is remove the pan, remove rod and main bearing caps and measure the clearance. Any major shop should have a pressure machine and you can check clearance without removing the bearing caps but will still have to drop the pan. Apply pressure to the oil gallery and see how much the oil flows out of the bottom of the engine. You could go to a heavier oil and get by for awhile but that would only be postponing the inevitable. Link to comment Share on other sites More sharing options...
Eagle Posted September 25, 2012 Share Posted September 25, 2012 First, what brand oil filter did you put on? If it's a Fram ... change it and report back what the oil pressure is. Second: Your MJ's oil pressure is FAR too high and you should not use that for a basis of diagnosis. The factory spec is (with the engine at operating temperature) 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. Every 4.0L I've encountered with under 100,000 miles on it has run 50 to 55 psi at 55 to 60 MPH, and idle typically is around 25 psi. The readings on your "new" XJ were within spec before you did the oil change, although lower than I would expect or than I would want to see. I would agree that (if a new oil filter doesn't make a difference) you probably need to replace the bearings. Link to comment Share on other sites More sharing options...
nitroxsteve Posted September 25, 2012 Share Posted September 25, 2012 My 88 4.0 with fresh everything including bearings runs 18psi at idle at operating temp and around 45 at crusing speed. Link to comment Share on other sites More sharing options...
Comanche County Posted September 26, 2012 Share Posted September 26, 2012 Perhaps a rear main that is starting to leak? Link to comment Share on other sites More sharing options...
HOrnbrod Posted September 26, 2012 Share Posted September 26, 2012 Don't do anything until you verify the gauge is reading correctly as compared to a known accurate mechanical gauge. The dash gauges are notoriously inaccurate and a corroded connection from the sender to the gauge will cause false readings. My pressure started reading high last month and I changed the sender - brought it back to normal. Verify you are looking at the correct pressure first to eliminate an electrical problem. Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 26, 2012 Share Posted September 26, 2012 Pure1 and straight 40W Link to comment Share on other sites More sharing options...
jeep_freek88 Posted September 26, 2012 Author Share Posted September 26, 2012 the guy i bought it from did the oilchange before i bought it and did use a fram filter along with mobile 1 5w 20 synthetic. the rear main has a slow drip as with most other 4.0 s that i have seen if i do the oil pump i will put a new rear main in. i have already done that with the mj. the mj oil pressure reads 75 psi when running cold and drops to 65ish when hot at speed and 40 at idle when warm. Link to comment Share on other sites More sharing options...
jeep_freek88 Posted September 26, 2012 Author Share Posted September 26, 2012 First, what brand oil filter did you put on? If it's a Fram ... change it and report back what the oil pressure is. Second: Your MJ's oil pressure is FAR too high and you should not use that for a basis of diagnosis. The factory spec is (with the engine at operating temperature) 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. Every 4.0L I've encountered with under 100,000 miles on it has run 50 to 55 psi at 55 to 60 MPH, and idle typically is around 25 psi. The readings on your "new" XJ were within spec before you did the oil change, although lower than I would expect or than I would want to see. I would agree that (if a new oil filter doesn't make a difference) you probably need to replace the bearings. you mean the crank bearings? Link to comment Share on other sites More sharing options...
jimoshel Posted September 26, 2012 Share Posted September 26, 2012 Which ever has the excessive clearance. Normally the rod s wear faster than the mains but not always. It can also be the cam bearings and loose lifters. Cam bearings have the least wear in an engine so they don't go out to often. Lifters get loose in their bore they let oil leak past them. Link to comment Share on other sites More sharing options...
mountainman Posted September 26, 2012 Share Posted September 26, 2012 For an engine with such miles, i wouldnt suggest 10/30. Id say run 10/40. So at this point you could dump a qt out and pour in a bottle of lucas oil stabilizer. It will increase the viscosity index one notch and you should see an oil pressure jump. But yeah also do the pressure test with a mechanical gauge to diag where your trouble may be in relation to what factory spec is. Link to comment Share on other sites More sharing options...
xjrev10 Posted September 26, 2012 Share Posted September 26, 2012 I've read that Lucus Oil stabilizer is not a good thing for our engines. I cannot remember but it was in one of those oil threads.. Link to comment Share on other sites More sharing options...
Eagle Posted September 26, 2012 Share Posted September 26, 2012 you mean the crank bearings? As Jim already wrote, more likely the rod bearings. But, as long as you're in there, it doesn't make sense not to replace everything. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 26, 2012 Share Posted September 26, 2012 Perhaps a rear main that is starting to leak? Rear main seals don't have any effect on oil pressure. Only leakage. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 26, 2012 Share Posted September 26, 2012 VERIFY the oil pressure with a gauge before doing anything else! The later XJs were notorious for having pi$$ poor oil senders. Answer Eagle's question about oil filters. What brand did you put on at the oil change. Link to comment Share on other sites More sharing options...
opsled Posted September 27, 2012 Share Posted September 27, 2012 Don't do anything until you verify the gauge is reading correctly as compared to a known accurate mechanical gauge. The dash gauges are notoriously inaccurate and a corroded connection from the sender to the gauge will cause false readings. My pressure started reading high last month and I changed the sender - brought it back to normal. Verify you are looking at the correct pressure first to eliminate an electrical problem. Would be my first move aswell.. opsled Link to comment Share on other sites More sharing options...
mjeff87 Posted September 27, 2012 Share Posted September 27, 2012 I run 20w50 in the 4.0 I swapped into my MJ (with unknown lineage). Bearings are sloppy and it sounds like a sewing machine, but it keeps a steady 20 psi at hot idle. Put 10w30 or 40 in it, and I have about 0-5 psi..... :rotf: Jeff (and yes, I've swapped sending units....twice) Link to comment Share on other sites More sharing options...
HOrnbrod Posted September 27, 2012 Share Posted September 27, 2012 Off-topic: Jeff, delete some on the messages in your mailbox - can not send you a PM. Link to comment Share on other sites More sharing options...
mjeff87 Posted September 27, 2012 Share Posted September 27, 2012 soon as I figger out where my inbox is at and how to do that, I will Don :yes: Link to comment Share on other sites More sharing options...
mountainman Posted September 28, 2012 Share Posted September 28, 2012 soon as I figger out where my inbox is at and how to do that, I will Don :yes: :rotfl2: ........ :thwak: ......... :group beer: Link to comment Share on other sites More sharing options...
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