Mud-wolf1

I got a 97 grand Cherokee 4.0 with around 240,000 miles ...my dad keeps putting15w-40 in it and it is real clattery till it warms up ... I know its way to heavy should I slick 50 my jeep and 5w- 30 or block restore or just Plain 5w-30?

fishbone

Don't put any magic potions in there. That's a sure way to end it's life early. Keep the oil changed, keep it full and put up with the chatter until it dies. Could last a day, could last for years like that. I've got a pick up with an 8 cylinder with similar mileage as yours and I've only used Castrol full synthetic 5w30 for the life of the truck without ever using any additives and honestly, it is still as quiet as the day I got it. Don't get me wrong, it's starting to burn some oil and I surely don't think it's going to last for another 200k but as for right now, all is good.

Mud-wolf1

dad just uses free 15w-40 idk brand

Mud-wolf1

thanks for the input

Nick-B

Unless you are living where you still have sub-zero temps, 15w-40 isn't too heavy for the 4.0.
Go ahead and try the 5w-30 and see what it does. Could be you just have a clattery motor. The 4.0 is not known for being super quiet. Its just an old-school design.

Mud-wolf1

got ya

jmonts

A lot of the XJ owners(myself included) are running Rotella T6 Diesel oil. It has some of the best ingredients for the tractor motor that is the 4.0. There are two weights but it really doesn't matter.
I noticed mine ran a tad quieter, but that could have all been perceived.

jmonts

Double post. Sorry. Stupid Wifi.

dave1123

Okay, guy. The reason the 4.0's valves clatter is the oil feed holes for the lifters are tiny and at idle don't flow enough oil to keep the valve lash closed. What seems to work best in them is 5W-30 Synthetic because it flows easier thru small ports then a thicker oil. The only reason to put thicker oil in a motor is if you have low oil pressure. Remember oil pressure is what floats the crank and rods and prevents metal-to-metal contact.

To put it in context, think about tranny fluid. It's as thin as water but has tremendous lubricity. It won't support a REALLY heavy load and that's why the clutches work, but it will lubricate ball bearings and gears.

Two different fluids for two different purposes.

Mud-wolf1

for the milage what oil should i get? heavy or what?

Kingfisher

I wouldn't use thinner oil in an engine with 240000 miles on it.

Maybe what your Dad is using is about right.

I have 198000 and use regular 10-30 Valvoline.

Maybe Rotella would be better. I don't know.

dave1123

In my opinion, if you're got 40 psi at idle, you're good to go. My 97 4.0 had 187K on her clock, so I switched to 10W30 and it got noisier. I went back to 5W30 and it quieted down. If you can't hold the 40 psi without going beyond 10W30, it's time for a rebuild.

My opinion, your choice. I wouldn't use ANY kind of additive except injector cleaner in the fuel tank.

As I've said, I've been told the reason the 4.0 is noisy is because the oil feed holes for the lifters are small so not much oil gets to them at idle. That's a plausible reason, but I've never had one apart to check that out. I know from experience in Chevy small block V8s, the oil gallery and the lifter bores actually intersect; that is, there is an egg shaped hole in the side of the lifter bores that is actually the oil gallery breaking thru. That's why if the lifter bores get worn, oil pressure plummets.

Firestorm500

I use 10W30 Mobil 1 and a Wix filter in both of my 4.0 XJs.

The '87 Renix does and has clattered a little on startup for about 50,000 miles now. It has 239,000 on the original engine. I replaced lifters at 180K miles and it had very little ring groove in the cylinder walls. There is plenty of oil moving around under the valve cover.

I'm going to run it till it won't run anymore.

I don't agree that you need 40 PSI at hot idle. Or that it's time for a rebuild if you don't. 13 PSI at hot idle is about the minimum, but some posters say theirs has had only about 4 PSI for years and it does fine.

dave1123

Okay, Firestorm. As long as the oil pressure comes up with the rpm, low idle pressure is okay. What worries me is an engine that doesn't have more than 20 when you're driving it. AND if you beat on an engine with low oil pressure, you're asking for trouble.

Firestorm500

Looks like his bearing clearances have opened up due to wear. Oil pressure stays low until they heat expand.

It's just about decision-making time for him.