Jeep 4.0 oil question.

95Trooper

Well-Known Member
Joined
Mar 23, 2008
Location
WNC
I just picked up a 1996 Jeep Grand Cherokee with a 4.0 in it to build as a daily driver (mostly) and some wheeling. It has 207,xxx miles on it as it sits. I bought it from the original owner. He said he always ran 10w30 in it since it was new but this last oil change which was recent he switched to 10w40. The Jeep has some lifter tick/piston slap when cold but goes away at operating temp for the most part. The previous owner said he made the switch to 10w40 to try to quiet down the lifter tick and it seemed to help from what he said.

The Jeep holds a steady 35-40 psi of oil pressure when warm. It's leaking a very little amount of oil around the head from what I can see but everything else looks virtually leak free. The piston slap goes away almost completely when the Jeep is warm after it has been driven for awhile and will idle quiet as a mouse. My question is, should I switch back to a 10w30 or just leave the 10w40 in it and roll with it? I've always been an advocate of running what the owners manual calls for. Winter is coming up so I wasn't sure if the 10w40 was too thick or not. Thanks for the help guys!
 
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The hotter the engine gets the thinner the oil gets. So if the noise goes away when the engine is warm I would think the thinner oil would be best. And that sounds more like lifters to me than a piston slap.
 
1997tj said:
The hotter the engine gets the thinner the oil gets. So if the noise goes away when the engine is warm I would think the thinner oil would be best. And that sounds more like lifters to me than a piston slap.
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It very well may be lifters I'm not sure. So, it would probably be best to go back to 10w30 then? I've already bought the Castrol GTX high mileage oil and a Mopar filter for it I was just second guessing changing it before I got some opinions from more experinced people than myself.
 
I'm putting 15W40 Rotella in mine this go-round.

Because why the fawk not.
 
1997tj said:
The hotter the engine gets the thinner the oil gets. So if the noise goes away when the engine is warm I would think the thinner oil would be best. And that sounds more like lifters to me than a piston slap.
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I might step into a yellow jacket nest, but, > 10 W 30/40/50, what ever, Means, as the oil is heated,it somewhat Thickens! That's not the technical term, but the "W" using paraffin's in the oil, lets it pour like its 10 weight, or whatever the bottom # is, but still provides the protection of the high #. I know it's Extremely hard to understand, & believe!
 
rodney eppes said:
I might step into a yellow jacket nest, but, > 10 W 30/40/50, what ever, Means, as the oil is heated,it somewhat Thickens! That's not the technical term, but the "W" using paraffin's in the oil, lets it pour like its 10 weight, or whatever the bottom # is, but still provides the protection of the high #. I know it's Extremely hard to understand, & believe!
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backwards, oil gets thinner as it heats. that means when it goes in it's the higher number, as it heats up it's the lower number.
 
shawn said:
I'm putting 15W40 Rotella in mine this go-round.

Because why the fawk not.
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Because you like your cam and lifters to last a long time. All of our pushrod, non-roller cam engines get the Rotella treatment. Cheap insurance IMO
 
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95Trooper said:
I just picked up a 1996 Jeep Grand Cherokee with a 4.0 in it to build as a daily driver (mostly) and some wheeling. It has 207,xxx miles on it as it sits. I bought it from the original owner. He said he always ran 10w30 in it since it was new but this last oil change which was recent he switched to 10w40. The Jeep has some lifter tick/piston slap when cold but goes away at operating temp for the most part. The previous owner said he made the switch to 10w40 to try to quiet down the lifter tick and it seemed to help from what he said.

The Jeep holds a steady 35-40 psi of oil pressure when warm. It's leaking a very little amount of oil around the head from what I can see but everything else looks virtually leak free. The piston slap goes away almost completely when the Jeep is warm after it has been driven for awhile and will idle quiet as a mouse. My question is, should I switch back to a 10w30 or just leave the 10w40 in it and roll with it? I've always been an advocate of running what the owners manual calls for. Winter is coming up so I wasn't sure if the 10w40 was too thick or not. Thanks for the help guys!
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Higher mileage (80,000+ miles) 4.0s will be noisy. To what degree is the only question. For the winter in Fayetteville, I wouldn't hesitate to keep 10w40 or even 15w40 Rotella in it. If you were in a colder portion of NC, I'd suggest a thinner oil for cold starts.
It's a 4.0, the lifters make noise, the pistons slap, etc. When it gets quiet you need to worry!
 
Jody Treadway said:
Bacuase you like you cam and lifters to last a long time. All of our pushrod, non-roller cam engines get the Rotella treatment. Cheap insurance IMO
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It should also help keep the oil pressure up on the trail.
 
Run it and listen to the noise....my Wife's WJ 4.0 had a tick at 75k when we I bought it (really cheap because the noise), I told her to put it out of her mind and roll. It got louder over the years and I picked up a 13k mile motor to put in it when it finally decided let go...at 185k it slung a rod out the side of the block and that was it. I put a motor in it and we sold it with close to 300k on it a couple of years ago. The oil weight / brand thing is only a peace of mind cure for your problem. I added Lucas every few changes and it did sound better, but the noise was still there. On really cold mornings it sounded like a little man with a hammer inside the motor.
 
I've always been hesitant about running a diesel rated oil in a gas engine. I'm thinking it has something to do with the far larger amount of detergents and zinc content. Otherwise, I love Rotella and always run it in my K30. With that being said, Rotella doesn't have as much zinc additive in it as it used to...in fact, MUCH less than it used to. 2007 emissions changes killed everything...ZDDP dropped way down, diesel fuel went ultra low sulfur, etc. When I changed the cam in my K30, Hamilton Cams said to run a quart of zinc additive through the first oil change to help protect the new tappets and cam as they wore together.

I'd absolutely run 10w-40 though. It usually doesn't get cold enough to bother it. I might would even try out 20w-50 if you were really concerned. However, as long as I didn't get a lot of metallic particles when I changed the oil, I'd just deal with the rattle or pull the head and drop in some new lifters.
 
Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. This is the best of both worlds and is accomplished by using special additives to increase viscosity with increase temperature.

Read more here: http://www.autoeducation.com/autoshop101/oil-change.htm
 
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