Elmore055

01 Grand Cherokee 4.0 L6 95,xxx Miles.

Lately I've noticed my jeep has been making a engine noise does not seem to be coming from the bottom end, quieter than a bad piston skirt. Oil pressure is good etc just did a fresh oil change yesterday, so my question is what could it be? I am newer to jeeps but not mechanics. I know naturally these are noisy engines, the jeep has always been well maintained and serviced on time. Also on a side note it started once the temperature here dropped been in the 20's lately. It appears to go away once completely warmed up when I did my oil change nothing came out with the oil and nothing seem to be blocking oil from flowing out. I am in need of a tune up and a downstream O2 sensor, randomly throw a misfire code occasionally. Any input is welcomed thanks.

dave1123

Welcome to CF!

You may have a little "piston slap" due to a slightly undersized piston or oversized bore. If it goes away soon after the engine warms, it's nothing to worry about. When I say "slightly" I mean like .005" or so. Production tolerances being what they are, it's not unusual to have a low-end sized piston put in a high-end sized bore. It just happens. However, if you ever crack a piston skirt, that will be the one.

The 4.0 has a reputation for longevity and being "bullet proof". I don't know about the bullet proof part, but they do last a long time with very little problems. Maximum torque is produced at 3000 rpm and the torque curve is a straight line from idle up to max and drops off sharply after that. Basically what I'm saying is twisting the **** out of it won't get you much except shortening it's life. Just remember you're pulling almost 4000 lbs with 195 horses. Treat her right and she could go to 300K.

4.0's do have some lifter noise at idle due to the oil supply ports to the lifters being small, but that's something they just do. Stand next to a 4.0 and a 4.7 when they are both running and you can tell which one is the 6.