My wife drives a 1990 Cherokee inline six with over 200,000 miles.

Since we have had it, we have always used 10w-30 oil in it.

What would be the outcome of using the same 15w-40 oil in it that I use in everything else around here??

It would be simpler to not need two different kinds of oil on hand.

It already has a minor oil leak and will need a quart about every 300 miles.

 

What does the owner's manual say?

You're in Kentucky, I wouldn't think it'd be a problem.


(And Long Live AMC! )

 

As a previous owner of a 1990 Jeep Cherokee, and 1992 Jeep wrangler I tried more than a few things to improve mileage.

I found that by installing bosch platinum plugs gapped .05 over recommended and the use of 5w-50 synthetic gained me almost 2mpg.

The heavier weight oils seemed to be the biggest factor in mileage.

At 200k if it is not burning oil then why change now?

Rick

 

There's nothing wrong with 15W-40 in a gasser. Diesel rated oils tend to have a lot of detergents and dispersants, so they do an excellent job of keeping the engine clean. The thicker oil will help with the oil consumtion a little bit, but don't expect miracles. And at 200k a thicker oil will help with hot oil pressure. I would use it.

Oil leaks on the 4.0 liter are often caused by excessive crankcase pressure due to the stupid constant PCV system getting clogged up. Does this truck oil the air filter regularly?

 

I replaced a bunch of black plastic crank-case vent tubes that went from the front of the valve-cover, through a block of vacuum ports, and then-I think-will have to look-to the breather.

Yes, I occassionally find oil in the breather.

Is there a fix??

Thanks.

 

http://www.off-road.com/jeep/cheroke...ltr/blowby.htm

Not permanent, but it will help unless the engine is too tired. Probably just leaky and plugged with carbon, though. Those 4.0's run a long time even when abused.