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Oil weight

I wonder what weight oil would be best in my 98 4.0 jeep 160,000 miles

First off, what viscosity was recomended when it was new ?
Does it show any signs of engine noise , smoking, or oil consumption?

My 130k Expedition and the former 130k 92 Explorer always just used their o.e. oil weight

What does the users manual say?

One more vote for whatever the owner’s manual says.

If you lost the owner’s manual, you can get a copy online.

Good Grief !!! How hard is it to make a decision on what kind of oil to use.

Hence the reason for my second question.
What is going on NOW . . different from the last 160k . . that would cause one to pose this query ?

So, now we wonder about such things as high mileage oil.

YET . . the OP has not replied yet to fill in the blanks.

If the manual is gone, the oil requirements might be upon the oil cap or a label under the hood.

I am wondering if this car has “badbearing”.

I’d bet money that without additional information everyone here is going to say “what does the owner’s manual say?” because that’s the only correct answer. If you don’t have the manual, and can’t find it designated on a sticker under the hood, try a Google search.

If there IS a problem of some sort, such as high oil consumption, say so and we’ll be happy to try to help.

I immagine the manual would say 10w30 for a 98 summer and 5w30 for winter, but yeah, the manual.

At least tell us which model jeep, and which engine.

His previous discussions dealt with a 98 Jeep Wrangler with a 4.0 engine.

How about high mileage castrol

1998 Wrangler 4.0L;

Engine Oil

API Classification SH or SH/CD or Above

Above 0°F (-18°C) 10W-30

Below 60°F (16°C) 5W-30

That makes sense . . .

One of my relatives has a 2004 Grand Cherokee 4.0 . . . and the manual says 10w30

Anyways, speaking of looking at the oil filler cap . . .

Several years ago, a colleague of mine at work walked over because his next job was a Prius, and he wasn’t sure what oil it got, because he had never worked on one.

I walked over, looked at the oil filler cap . . . saw that it was obviously a factory cap . . . and said “5w30” and then I walked away and went back to work

There was no owner’s manual in the glove box, and he wasn’t very computer savvy . . . or else he might have looked up the owner’s manual online. And he didn’t think to look at the cap. To be fair, I’ve worked on some Toyotas where the cap doesn’t say

I’ve noticed that many factory oil filler caps say the viscosity, yet many/most aftermarket caps do not. Perhaps OP has lost the factory oil filler cap and is using an aftermarket

Recent engine knock. 10-30 Summer. I got that. Just thought maybe after 160,000 miles a different weight might be better.
Engine knock occurred after i put lucas in and then drove to the high rockies where it was still freezing at night. Coincidence?
Engine has never used oil…

knock? do you mean pinging? You might try a higher octane gas, there may be carbon buildup.

Oil won’t change pinging. Serious pinging will cause engine damage.

My 1991 Jeep Cherokee 4.0L used the recommended 10W-30 year round for it’s entire 10 year/150,000 mile life span.

Its not pinging…

Ok lets try this… Is it ok to put synthetic in an engine that has had conventional its whole life?