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  1. #1
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    Default Jeep 4.0 High mileage oil weight

    18 months ago when I bought the YJ, it had 200k kms, and engine was leaking ( rather hemorrhaging) from rear main, out of the dipstick, and the valve cover.
    I replaced the rear main seal, valve cover gasket and fixed the CCV system which some genius disconnected and routed with a long pipe down to the diff
    I cleared the blockage and fixed all the CCV pipes and the oil pressure returned to normal and no more blow by out of the dipstick

    The motor was full of sludge, I changed the oil 3 times in the subsequent weeks to get the motor "clean" I did not want to make use of engine flush, as this could have caused more leaks.

    I changed the oil initially Castrol GTX 20w50 high mileage and subsequently to normal GTX 20w50 because the high mileage version was discontinued. The leak from the rear main went away, but after about 7k kms it has started leaking again. I am assuming that the oil viscosity has reduced hence the leak again.

    My plan is as follows: Replace the rear main seal again, replace the sump gasket and replace the oil with SHell 25w 60 high mileage oil.

    I've read that the 4.0 loves 10w-40 but want to know if the high mileage 25w 60 will be a better idea. The motor has some minor "knocking" and intermittent ticking, which is apparently normal for older 4.0 inline 6's

    thanks for your input
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  2. #2
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    Default Re: Jeep 4.0 High mileage oil weight

    The knocking and ticking....When hot or cold?

    I run 10w40 in mine and it runs fine. Rear main leaks a bit but it's not bad enough to worry about really.

    I had 20W50 in it before and it would often get crazy lifter noise on startup when cold. 10W40 stopped that completely. That said, I only have 170k kms on mine.
    Stu.
    Current:
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    KTM 1190 Adventure

  3. #3
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    Default Re: Jeep 4.0 High mileage oil weight

    "ticking" normally when cold, but the ticking I hear on acceleration only, so it could be a leaky exhaust manifold ( comes and goes as well)
    The "knock" comes and goes at any temperature. Thought it was a rod knock a few months back, but kept driving it. Mechanic said of it was a rod knock the engine would have failed by now.

    One would assume if the oil is thicker it would quiet the motor down?

    On the rear main seal, do the later 4.0 motors have a 1 piece or 2 Piece seal? Mine has a two piece and both my Wranglers with the 4.0 motor have leaked on the rear main, maybe retrofit a new one piece seal to solve the problem?
    Last edited by backmarker; 2018/03/07 at 09:43 AM.
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  4. #4
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by backmarker View Post
    "ticking" normally when cold, but the ticking I hear on acceleration only, so it could be a leaky exhaust manifold ( comes and goes as well)
    The "knock" comes and goes at any temperature. Thought it was a rod knock a few months back, but kept driving it. Mechanic said of it was a rod knock the engine would have failed by now.

    One would assume if the oil is thicker it would quiet the motor down?
    I have a 98 XJ with a 4lit that has seen more low range work than most... and still does! I'm not lying if I say we use 4x4 at least twice per week. Happiness is... But, this also means that the engine worked harder than average for the amount of kilo's on the clock.

    I've also started noticing serious drop in oil pressure when I'm working it hard in the dunes on a hot day. So. I'm using 20W50 and the Jeep is as happy as a pig in mud....

    As far as the knock goes, it could be a bit of pistons slap, or even a cracked flex plate. I would guess the first is more likely. If it gets serious, it can break off a piston skirt, and then you'll know about it. It's not uncommon on the 4lit I6.
    Work. It's a wealthy man's privilege, and a poor man' fate....

    André Opperman


    "Boerbok" - 98 Jeep XJ 4lit auto
    "Gloria" - 04 Ranger D/C 4lit auto

  5. #5
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    Default Re: Jeep 4.0 High mileage oil weight

    My '99 XJ still purrs with over 340k km's, it only gets 10w40 Magnatec. Mine developed a leak at the cam cover close to the firewall about a year ago, but a new genuine gasket sorted that out quickly. Never had knocking/ticking problems.
    2004 PRADO VX 4.0 V6

  6. #6
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    Default Re: Jeep 4.0 High mileage oil weight

    Just my opinion, but if you're running 20W50 to maintain some oil pressure, it's time for some engine work.
    Jakes Louw
    2012 Jeep Sahara Unlimited 3.6 V6
    Percivamus

  7. #7
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by jelo View Post
    Just my opinion, but if you're running 20W50 to maintain some oil pressure, it's time for some engine work.
    And you are entitled to it.

    The oil pressure just drops when very hot and gunning it in the dunes. But, I suspect there's been some damage a year or so ago when the engine ran dry and overheated. Slight tapping sound since. But heating issues sorted, runs nicely on target, never hotter than 103deg, doesn't smoke, and doesn't use a drop of oil.

    I started using 20W50 as a precaution, and it seems to work very well.
    Work. It's a wealthy man's privilege, and a poor man' fate....

    André Opperman


    "Boerbok" - 98 Jeep XJ 4lit auto
    "Gloria" - 04 Ranger D/C 4lit auto

  8. #8
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    Default Re: Jeep 4.0 High mileage oil weight

    Oil pressure is dandy, its the damn rear main that's the pain in my ass.
    So for the interim I'm going to run the 25w- 60 to slow down the leak until i an get new gaskets, rear main will be ex-US
    this morning the motor was quiet sounded like it should

    Ill do the oil change this weekend, and revert back with my findings, hopefully not an engine rebuild
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  9. #9
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by backmarker View Post
    Oil pressure is dandy, its the damn rear main that's the pain in my ass.
    So for the interim I'm going to run the 25w- 60 to slow down the leak until i an get new gaskets, rear main will be ex-US
    this morning the motor was quiet sounded like it should

    Ill do the oil change this weekend, and revert back with my findings, hopefully not an engine rebuild
    Just some feedback for those that at interested.

    After adding the 25w-60 oil, the motor is definitely quieter . The rear main oil leak speed has reduced to a point that is almost negligible. So far so good. Once I have gaskets ill do the rear main seal again, at least this bought me some time.

    Ill run a lighter weight once the seal is replaced and see what happens.
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  10. #10
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    Default Re: Jeep 4.0 High mileage oil weight

    My Jeep mechanic reckons once the main seal leaks there's probably a bit of wear of the crank and even a new seal will only help for a little while. I clean mine when it starts bugging me and then pretend it isn;t leaking
    Stu.
    Current:
    06 Wrangler Sahara. 3.5inch Rubicon Express and Bilstein lift, Metalcloak control arms, 1.25" RC Body Lift, 1" JKS MotorMount Lift, Zone Disconnects, BFG KM2 33's
    NO LOCKER NEEDED!!!
    KTM 1190 Adventure

  11. #11
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by roadhawg View Post
    My Jeep mechanic reckons once the main seal leaks there's probably a bit of wear of the crank and even a new seal will only help for a little while. I clean mine when it starts bugging me and then pretend it isn;t leaking

    I'm considering rebuilding/restoring the whole vehicle once I have another form of transport. I've replaced pretty much every seal you can think of.. standard issue when you have a 27 year old 4x4..

    Will start a thread on it when the time comes.... I wonder how hard it is to import a Mopar 4.7 Stroker with a Edelbrock Performer cylinder head, Full Borla S/S exhaust system...... the list goes on

    I have lots of plans for this vehicle, seems like a lifetime project that will carry on until I get it perfected
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  12. #12
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    Default Re: Jeep 4.0 High mileage oil weight

    I thought i'd share an update:

    Good thing is the Jeep is no longer leaking from the rear main seal.
    However engine noise is back, no ticking anymore but the knock is persisting and seems like it is here to stay, where in the past it came and went. I'm now worried about crank damage, and or rod breaking.


    My options as I see it: ( I do not want to drop a V8 in)

    1.Drop in a 2nd hand TJ/XJ/WJ 4.0, I would have to mod the engine mountings, retrofit ignition system.I also think the older cylinder head might not work with the newer spec 4.0 motors.

    Then I would also possibly get a motor that is also kaput,

    2.Order new components from the states: Pistons, Rings, Rods, Bearings, Pumps, Cam, Pushrods, and valve gear. Have it rebuilt by a reputable engineering shop in SA.

    3. Order a rebuilt stroker complete from US

    Questions:

    1.Are remanufactured 4.0 motors available in SA?
    2.If i were to order engine internals from the US, ( which brand/company would be recommended)
    3.An engine shop that will do a rebuild that is of the highest standard.

    Thanks in advance.
    Last edited by backmarker; 2018/03/26 at 01:25 PM.
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  13. #13
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    Default Re: Jeep 4.0 High mileage oil weight

    I am disappointed that a V8 isn't on that list
    Stu.
    Current:
    06 Wrangler Sahara. 3.5inch Rubicon Express and Bilstein lift, Metalcloak control arms, 1.25" RC Body Lift, 1" JKS MotorMount Lift, Zone Disconnects, BFG KM2 33's
    NO LOCKER NEEDED!!!
    KTM 1190 Adventure

  14. #14
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    Default Re: Jeep 4.0 High mileage oil weight

    all I have to say is this:

    "Just my opinion, but if you're running 20W50 to maintain some oil pressure, it's time for some engine work."

    but everybody here is much brighter than me it seems
    Jakes Louw
    2012 Jeep Sahara Unlimited 3.6 V6
    Percivamus

  15. #15
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by jelo View Post
    all I have to say is this:

    "Just my opinion, but if you're running 20W50 to maintain some oil pressure, it's time for some engine work."

    but everybody here is much brighter than me it seems
    I've just conceded I need engine work sir just got pricing on all the internals barring a new crankshaft and camshaft.

    Block internals 20k
    Cylinder head internals 5k
    1985 Toyota Fj45 Landcruiser 4.2 P/U (Sold),
    1991 Jeep Wrangler YJ 4.0 Sport (Sold),
    2006 Toyota Hilux 3.0 D4D D/C Raider (Sold),
    1984 Suzuki Sj410 1.0,(Sold)
    1991 Jeep Wrangler YJ 4.0 Renegade
    2007 Jeep Wrangler JKU 3.8 Sahara
    2014 Jeep WK2 3.6 Overland

  16. #16
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by backmarker View Post
    I've just conceded I need engine work sir just got pricing on all the internals barring a new crankshaft and camshaft.

    Block internals 20k
    Cylinder head internals 5k
    well I'm with Roadhawg on this one, sorry
    Jakes Louw
    2012 Jeep Sahara Unlimited 3.6 V6
    Percivamus

  17. #17
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    Default Re: Jeep 4.0 High mileage oil weight

    Quote Originally Posted by jelo View Post
    all I have to say is this:

    "Just my opinion, but if you're running 20W50 to maintain some oil pressure, it's time for some engine work."

    but everybody here is much brighter than me it seems
    This. My old 4l grand got to 265k miles befors I parked it, and the engine was quiet, didn't burn oil or leak and ran fine, just used 10-40 semi synth and changed every 6k miles. I'd be looking for another 4l to drop in, a looked after one will do many miles
    Cheers
    Steve Wright

    2007 Grand Cherokee CRD Overland
    2020 Renegade Limited S, SWMABO's ride
    Previous Jeeps- 8 XJs, 3 KJs, 3 WJs, 2 TJ's, an MJ & a '17 Renegade

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