High milage jeep, looking for a few answers...

Messages
471
Location
Balto, MD
Im looking to do an oil change. Im starting to get the normal weeping at the rear main seal. Its not leaking but I do see some blow by under the car. Its a 4.0l with 220,000 and its an AMC in-line 6. 1) So with that being said, what is a good high mileage engine oil that will help to sell seals? 2) I would use 10w-30 normally, but with it being a higher mileage car should I run a higher weight oil? 3) What about rotella 15-40? I know its not high mileage, but I know its pretty good. 4) I think Id like to go non-syn just because the "synthetic" can leak thing plays over and over in my head haha. Is that true that 100% synthetic oil can leak in a high mileage car? 5) Also, I was wondering about running TCW3 oil in my gas will help the idle and starts better? If so how much? 4) Also, should I maybe run a good oil with detergent in it to help clean the engine out? I picked this up, so Im unsure on the history. Or I could run something in there now ( like mystery oil or something ) and then drain and fill with high mileage oil. Thanks!!
 
Messages
35,797
Location
NY
Originally Posted By: NattyBoh
Im looking to do an oil change. Im starting to get the normal weeping at the rear main seal. Its not leaking but I do see some blow by under the car. Its a 4.0l with 220,000 and its an AMC in-line 6. 1) So with that being said, what is a good high mileage engine oil that will help to sell seals? ANY BRAND 5w30HM OIL SHOULD BE FINE. I SUGGESTED 5w30 BECAUSE IT WILL AID WITH COLD STARTS, WINTER IS JUST AROUND THE CORNER. 2) I would use 10w-30 normally, but with it being a higher mileage car should I run a higher weight oil? NOT UNLESS THE LEAK GETS WORSE OR YOU START TO BURN OIL. 3) What about rotella 15-40? I know its not high mileage, but I know its pretty good. NOT WITH WINTER COMING. hide I'D PREFER A 5w40 IF I WAS GOING TO USE A 40 GRADE OIL. 4) I think Id like to go non-syn just because the "synthetic" can leak thing plays over and over in my head haha. Is that true that 100% synthetic oil can leak in a high mileage car? DINO HM OIL IS FINE. 5) Also, I was wondering about running TCW3 oil in my gas will help the idle and starts better? If so how much? IT MIGHT HELP 1 OUNCE/5 GALLONS OF GAS. I THINK IT HELPS WITH RING SEAL IN OLDER ENGINES WHICH IS WHY A LOT OF PEOPLE CLAIM IT IMPROVES THEIR IDLE. HOT TOPIC FOR HEATED DEBATES. I THINK IT HELPS. 4) Also, should I maybe run a good oil with detergent in it to help clean the engine out? I picked this up, so Im unsure on the history. MOST HM OILS DO SOME CLEANING. Or I could run something in there now ( like mystery oil or something ) and then drain and fill with high mileage oil. ADD A PINT OF MMO TO THE OIL 1000-1500 MILES BEFORE YOU CHANGE IT. Thanks!!
I'll give me opinion in CAPS.
 
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2,415
Location
SD
I agree with demar for the most part. Personally, though, on a 4.0 w/ that mileage, I'd stick w/ a 10W30 HM.
 
Messages
4,659
Location
Massachusetts
I'm a long time Jeep owner and off road enthusiast. Personally, I don't think you need to step up to a 40wt in the winter. I actually run 5W30 in most of my rigs in the winter, but 10W30 would be fine for MD. I have had good luck with Supertech HM oil in other applications. I also like the Quaker State HM oils. Regarding synthetic: Many here would say that "syn leaks" in a higher mileage application is a thing of the past. I have personally experienced it a couple of years ago. My entire engine started to seep: valve cover, oil pan gasket, even the threads on the OP sending unit! This all started happening after one commute to work on a Monday after the change (which was Supertech Syn 5W30). I've used the oil a bunch of times in other vehicles and all was well, but for some reason the 1.6L in my Tracker didn't like it. I drained the syn (into a clean container!) and ran QS 5W30 HM oil, to which all leaks stopped after my work week was done. It was the weirdest thing ever, but definitely changed my view on switching to syn after a life on dino. Given that the rear main is only starting to seep, I would run Quaker State HM or Supertech HM oil in the 10W30 flavor and run it until Spring. Order up a bottle of Auto RX (which has worked for me) and run a decent 10W30 dino per instructions. The AutoRX will not only clean things up a bit, but it will also help your seals too.
 

OVERKILL

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46,201
Location
Ontario, Canada
Curious as to why all the recommendations for 10w30 over 5w30.... Both are likely going to be the same price, the same weight when hot, but the one will provide much better cold flow than the other..... 5w30 would be the no-brainer......
 
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2,750
Location
Rochester, NY
The 4.0 has no issue with a 40 weight. I've been running T6 5W-40 in my mom's for about 2 years now (it's got 101k on it), and it loves the stuff. Has no issues building pressure immediately in the single digits either. It hasn't developed any new leaks since switching (from cheap 10W-30 dino), and the very slight rear main leak it has (almost all 4.0s do) hasn't gotten worse. Any good 5W-30 or 5W-40 should be just fine for the engine, choose based on price, availability, etc.
 
Messages
4,912
Location
Lakeville, MN
Past experience with running a dino 5w30 and dino 10w30 is why I choose to run 10w30 most of the time. The 10w30, per the (admittedly non-precise) oil pressure guage, seems to hold better oil pressure at hot idle and hot cruising than 5w30 does. I don't have an issue running 5w30 in winter, but in the summer, I stick to 10w30.
 

NattyBoh

Thread starter
Messages
471
Location
Balto, MD
Yeah that is the other thing I forgot to add, was the oil pressure at 2k RPM cruising on the highway it at around 50psi. I think thats good for that engine, but if its been running for a while and I come to a stop in traffic or a light, the gauge will gradually drop down to say around 10 psi.... I think hot idle on these is actually 13psi. It would normally stay around 20psi hot, but recently seen it around 10psi. Is there a brand that is better than another in terms of cleaning and seal swelling.. this isnt a daily driver, so for me to use a cleaner like AutoRX might not be a good idea. It doesnt get much drive time. Its actually an off road rig. And i would run EITHER MMO ir TCW3 right?
 
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OVERKILL

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46,201
Location
Ontario, Canada
Originally Posted By: MNgopher
Past experience with running a dino 5w30 and dino 10w30 is why I choose to run 10w30 most of the time. The 10w30, per the (admittedly non-precise) oil pressure guage, seems to hold better oil pressure at hot idle and hot cruising than 5w30 does. I don't have an issue running 5w30 in winter, but in the summer, I stick to 10w30.
It could be that the 10w30 was just a heavier oil than the 5w30 you were using. Did you compare the HTHS values between the two? All kinds of fun variables wink
 
Messages
35,797
Location
NY
Originally Posted By: OVERK1LL
Curious as to why all the recommendations for 10w30 over 5w30.... Both are likely going to be the same price, the same weight when hot, but the one will provide much better cold flow than the other..... 5w30 would be the no-brainer......
That's what I thought too.
 

NattyBoh

Thread starter
Messages
471
Location
Balto, MD
Yeah that is the other thing I forgot to add, was the oil pressure at 2k RPM cruising on the highway it at around 50psi. I think thats good for that engine, but if its been running for a while and I come to a stop in traffic or a light, the gauge will gradually drop down to say around 10 psi.... I think hot idle on these is actually 13psi. It would normally stay around 20psi hot, but recently seen it around 10psi. Is there a brand that is better than another in terms of cleaning and seal swelling.. this isnt a daily driver, so for me to use a cleaner like AutoRX might not be a good idea. It doesnt get much drive time. Its actually an off road rig. And i would run EITHER MMO ir TCW3 right? Is there a container I can buy that measures it out and then I can put it in the tank? I think I remember something like HEAT or another gas additive had a similar bottle to this. It was like a built in measuring bladder. You would squeeze it to fill up a certain part of the bottle and then it would just dispense that amount you squeezed into that bladder
 
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OVERKILL

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Messages
46,201
Location
Ontario, Canada
I'd use Mobil 1 HM if you are keen on a HM oil. I wouldn't run anything in your oil or fuel. I'm not a fan if additives in general. If a vehicle has been properly maintained, there should really be no need for them.
 

NattyBoh

Thread starter
Messages
471
Location
Balto, MD
Thats the question, I dont know what the history is like. It does have a slightly sough idle, so I bought a cap, rotor, wires and plugs. Unsure if that would help but for 60 bucks, ehh I'll do it.
 
Messages
4,912
Location
Lakeville, MN
Thought I had replied earlier, guess not. My Cherokee is an '88, so its seen a lot of different oils in its lifetime - I believe the original specification is for an SF rated oil! Regardless, in hot summer weather, the hot idle and hot cruise pressure has always been lower using a 5w30 in hot weather than the 10w30. I am a bargain priced name brand dino user in this vehicle, so its been whatever was on sale at the time I needed it - no fancy HTHS comparisons! Running 10w30 gets me 20 psi at hot idle and 55 psi or so on hot cruise repeatedly, and UOA's I once did showed it worked well. I do run 5w30 in thwe winter, but come hot weather the pattern repeats itself, so I go back to 10w30. Regardless, the basic take home message is that the 4.0 will tolerate most any oil thrown at it, and doesn't need a lot of fussign with fuel additives and the like.
 
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701
Location
Northern IL
I agree with the no addatives in the engine oil but as far as fuel is concerned I reccomend using Seafoam to clean the lines and injectors. The reason being si that we have no control over what gunk builds from the gas in the tank and so to help prevent this along with moisture buildup I run seafoam every other OC. For oil I would run what I run in my bro's cherokee which is Supertech High Mileage 10w40. Its a great price and does well in the motor. Definitely dont use 15w40 with your winters there it gets too cold 5w40 would be ideal but you would have to step up the price range for that. If you were willing though MObil TDT 5w40 would be a great choice.
 

NattyBoh

Thread starter
Messages
471
Location
Balto, MD
Thanks guys . Reason for the fuel additives was the slightly rough idle and slight engine noise. Nothing major, well doesnt seem like it. Mechanic said normal noise for a 220,000 mile engine. The TCW3 might help lube it up , but MMO would lube a bit and clean too..
 
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8,138
Location
Mahzurrah!
Rotella 10w30, a heavy thirty that's so packed with additives/detergents it puts most HM oils to shame and it's not expensive either.
 
Messages
712
Location
Wenatchee, W.A.
I LOVE threads about Jeep 4.0s, especially Cherokees. Ive got 6 XJs, four of which have 4.0 Inline 6 motors. I am dealing with your exact issue of weeping rear main, and recently front main seal with my 87, which has 292,3?? miles on her Original factory Everything. Ive said it before, and Ill say it again, I am a big fan of 10w-30 conventionals for Tight, Low mileage 4.0s in any weather, and 10w-30 and 10w-40 conventional oils for High mileage or worn 4.0s. A good quality 10w-40 conventional for a Reasonable OCI is what most 4.0s would like regardless of where they are and what the weather is. I dont think these old school technology motors like 5w-30 oils coursing through their cast iron veins, At least the worn out 4.0s that keep running and running with neglect and hard driving conditions for 250,+++ miles. My 96 has 249,??? miles on its original motor, has been Driven hard and put away wet, dry, however you want to look at it, and actually sounds and performs like a Healthy motor. I Love my 4.0s, and choose to run Conventional 10w-40 oils(Usually Quaker State or Castrol) in them. I also always use a Oversize oil filter on my 96, 99, and Beloved SilverStone Metallic 01.
 
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