Jeep 4.0 sounds like Mercedes diesel at idle

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Hey all, I have a 97 XJ with 220,000 miles. I bought it at 184,000. I first used the Farm & Ranch stores MAG1 10w-30 with Auto-RX through two clean & rinse cycles, changed the head gasket and resealed the bottom end, and then used Shell Rotella T5 10w-30 twice at short intervals. I wanted to cut open the filters and make sure no debris from the engine work. It was quiet the entire time. Then I switched to Amsoil synthetic. Immediately after the oil change, when idling it sounded like a Mercedes diesel after a warm start. It goes away at RPM. I used 4 quarts of HDD and 2 quarts of AME. I drove it about 13,000 miles and changed the oil this time using 3 quarts of HDD and 3 quarts of AME. The diesel noise is still there. Oil analysis shows better than when using mineral oil. This is my second 4.0. I have another one in an 01 XJ with 340,000 that I've been using synthetics in for over 300,000 miles and have been using Amsoil for the last several years. In that one I've run mostly the thicker AMO 10w-30 or AME 15w-40. It sounds fine except for a lifter tick. I am wondering why the sudden change in noise with going to synthetic. It literally went from quiet (not even lifter noise) to a diesel with the synthetic. No other work was done between the oil change. I am considering trying AME 15w-40 in this engine, or trying another round of Rotella T5 10w-30 or even the Rotella T6 5w-40 at the next oil change. Any suggestions? I've had Mercedes diesels for years and it really does sound like one at idle!
 
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Originally Posted By: brian
Hey all, I have a 97 XJ with 220,000 miles. I bought it at 184,000. I first used the Farm & Ranch stores MAG1 10w-30 with Auto-RX through two clean & rinse cycles, changed the head gasket and resealed the bottom end, and then used Shell Rotella T5 10w-30 twice at short intervals. I wanted to cut open the filters and make sure no debris from the engine work. It was quiet the entire time. Then I switched to Amsoil synthetic. Immediately after the oil change, when idling it sounded like a Mercedes diesel after a warm start. It goes away at RPM. I used 4 quarts of HDD and 2 quarts of AME. I drove it about 13,000 miles and changed the oil this time using 3 quarts of HDD and 3 quarts of AME. The diesel noise is still there. Oil analysis shows better than when using mineral oil. This is my second 4.0. I have another one in an 01 XJ with 340,000 that I've been using synthetics in for over 300,000 miles and have been using Amsoil for the last several years. In that one I've run mostly the thicker AMO 10w-30 or AME 15w-40. It sounds fine except for a lifter tick. I am wondering why the sudden change in noise with going to synthetic. It literally went from quiet (not even lifter noise) to a diesel with the synthetic. No other work was done between the oil change. I am considering trying AME 15w-40 in this engine, or trying another round of Rotella T5 10w-30 or even the Rotella T6 5w-40 at the next oil change. Any suggestions? I've had Mercedes diesels for years and it really does sound like one at idle!
I've had some noise when switching from dino to synthetic which went away after a bit. YOu said you used 4 HDD and 2 AME....are these the heavy diesel oils? In your place maybe consider going to the Amsoil 10w30 and see how it performs. Even though the 4.0 generally prefers heavier oils, your may not.
 
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I would check your oil pressure with a gauge-bet it's getting low at hot idle (like my '98 4.0 in my sig), might be time to switch to a heavier weight. I'm personally going to 10W40 once the hot weather gets here.
 
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I have the same diesel noise issue you mentioned. After an oil change, I would also get a slight tick even when at operating temperature for the first few thousand miles. Always used either Pennzoil conventional or Pennzoil HM 10w30. This go around, per BITOG member KCJeep's recommendation, I used 5 quarts of 10w40 and watered it down with a 5w20. The running while hot tick is gone, but I still get a tick during the warm up cycle which is fine.
 
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Oh, that's pretty bad! Have you dropped the pan and checked to oil pickup screen? I'd do that ASAP. Or just use a cheap borescope to do that, if you don't want to redo the pan sealing.
 
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Our four cylinder Mercedes diesels sounded really good at idle after warm-up. Maybe your Jeep is just running really well?
 
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Noise generally means contact of some sort... Maybe it's lubed contact, but why go there? Why would you keep using full synthetic when the engine is noisy? Why not run Maxlife 10W-40 for one change and see how it sounds? Do you think that Amsoil will keep your motor alive longer or something ...
 
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4.0's like to mutter and grumble at idle, that's for sure. The one in my .sig (now my daughter's) is a lot quieter than the 2001 I had for a while, but at idle there is just a little "grumbling" they all do. Some oils make it more audible, but noise does not necessarily mean 'wear,' it just means that some oils don't muffle the noise of parts moving as well as another oil might. When an engine "sounds like a diesel," it frequently is piston slap and that's a harmless noise that DOES vary a lot with different kinds of oil. But it could also be bearing clearances or wrist pins. In my experience, Jeep 4.0s really tend to do better on thicker oil than the recommended 5w30 or 10w30, and seem to respond especially well to Rotella T6 synthetic 5w40. I'm betting on low oil pressure at idle being a contributor- a good percentage of 4.0s tend to wear open the cam bearing clearances (of all things!) and that drops the pressure even though its harmless once the wear pattern stabilizes. My 2001 got to the point that the oil light would come on in hot weather, even with T6 5w40. No change in sounds or anything, so in went a high-volume oil pump and all was well again. Its still running, I stay in touch with the new owner who is friend of my daughter's.
 
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Use dino oil in that 4.0 i tried PP once when i had mine and it sounded like there were marbles in the crankcase switched over to a high Mileage 10w30 and after the second oil change it was quiet again.. Also those engines build up carbon especially if you use high test. use some techron in the gas and maybe do a very slow water drip into the intake to get rid of some of the carbon.
 

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Thanks for your responses. I am fairly confident oil presssure is not the issue. When I first went to buy it, the gauge would read between 10-15 psi at idle, often hitting 10, after just 5 minutes of driving. I suspected the sending unit was bad. I put a mechanical gauge on it and it was something like 17 which is more reasonable. Oil pressure at RPM is 40-50 as expected. It may very well be lifters. I can say that if I ever pull the heads off either again, they are getting lifters. At the time I pulled the pan to change the rear main seal and reseal the rest of the bottom end everything looked fine. Oil analysis still doesn't show any rear bearing problems. I may try 5 quarts of AME 15w-40 + 1 quart of HDD 5w-30 similar to the 10/40 + 5/20 idea suggested.
 
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I know exactly the sound you are describing. Mine will do it very noticeably on Rotella and Maxlife. From what I have seen in UOA's it has nothing to do with wear. It can be annoying however. Try some plain old PYB in it I bet it goes away in 1,500 miles or so.
 
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Originally Posted By: brian
Thanks for your responses. I am fairly confident oil presssure is not the issue. When I first went to buy it, the gauge would read between 10-15 psi at idle, often hitting 10, after just 5 minutes of driving. I suspected the sending unit was bad. I put a mechanical gauge on it and it was something like 17 which is more reasonable. Oil pressure at RPM is 40-50 as expected. It may very well be lifters. I can say that if I ever pull the heads off either again, they are getting lifters. At the time I pulled the pan to change the rear main seal and reseal the rest of the bottom end everything looked fine. Oil analysis still doesn't show any rear bearing problems. I may try 5 quarts of AME 15w-40 + 1 quart of HDD 5w-30 similar to the 10/40 + 5/20 idea suggested.
I seriously doubt that its any major mechanical issue at all given that you've got good oil pressure (assuming the 10-17 holds when it is fully hot, not just warmed up a few minutes). I suspect the oil you're using is just one of the ones that tends to make piston slap more audible- lifters will NOT sound like a diesel, they sound like a room full of sewing machines. I'm telling you- Rotella T6 is the oil for the 4.0.
 
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Originally Posted By: fdcg27
Our four cylinder Mercedes diesels sounded really good at idle after warm-up. Maybe your Jeep is just running really well?
What kind of Mercedes diesel? An older mechanical injection unit or a modern computerized engine?
 

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Originally Posted By: artificialist
Originally Posted By: fdcg27
Our four cylinder Mercedes diesels sounded really good at idle after warm-up. Maybe your Jeep is just running really well?
What kind of Mercedes diesel? An older mechanical injection unit or a modern computerized engine?
1980's Mercedes OM617/602/603 with indirect injection.
Originally Posted By: crazyoildude
Use dino oil in that 4.0 i tried PP once when i had mine and it sounded like there were marbles in the crankcase switched over to a high Mileage 10w30 and after the second oil change it was quiet again.. Also those engines build up carbon especially if you use high test. use some techron in the gas and maybe do a very slow water drip into the intake to get rid of some of the carbon.
I've been using Shell or Conoco as they are the top tier fuels that are available here. With our high altitude, 85 octane is "regular" which is what I use. When I travel in/towards California I use Chevron whenever possible and choose 76 gas as a second. The last Techron treatment was about 35,000 miles ago when I first got it. Since the head was off, milled, valve job & seals just about 23,000 miles ago I'm not sure there's any major carbon build up on the valves yet. And before I pulled the head compression was 150-160 so I think the rings are good. I'd really like to use a synthetic in this engine like I can in the other one. I tend to drive them a lot and like the 12,000 mile drain intervals I can do with the HDEO synthetics. Maybe this 97 is just a looser engine with some piston slap and I won't be able to. I wonder if the Group III Shell T6 5w-40 is better than the high ester oil I'm currently using? I'll post back after I change the oil in my 01 XJ. I'm going to put the same oil in it (HDD 5w-30 + AME 15w-40 50/50 ratio) as I'm currently running in the 97 XJ and see if it develops any new noises. I'll also update with what I do in the 97 XJ and if it makes the noise go away. Thanks.
 
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Originally Posted By: brian
I wonder if the Group III Shell T6 5w-40 is better than the high ester oil I'm currently using?
Maybe for the application. Predominantly ester oils have great numbers for things like HTHS, but in the real world I've noticed a lot of times that people report differences in sound or get UOAs that make them go back to more pedestrian synthetics or even conventionals.
 
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