Hello, I have a 2000 Jeep Grand Cherokee Laredo 4.0, 6 cylinder with nearly 160,000 miles. I started hearing a knocking noise that got louder as it got colder up here in Alaska. At first I believed it was the flex plate but I had my mechanic inspect it and he said it is most likely rod knock. He said that it doesn’t sound too terrible yet and that he has heard cars that sound way worse that last forever. I was just wondering if there is anything I can do to help it at all for cheap. I just did an oil change about 2 weeks ago. The noise is definitely louder when first started up than it is when the vehicle is at operating temperature. Anyways, if anyone has any ideas, let me know thanks! (I’m hoping to keep it for around 2 more years. Just bought it couple months ago and I didn’t really notice the noise because it was summer and warmer and hadn’t really been driven)
4.0 are famous for part of a piston skirt breaking off. Its purpose is to stabilize the piston in a up down motion, whereas the connecting rod is trying to push and pull it "sideways".
Usually its the 2nd piston from the firewall.
Unplugging injector and compression test will usually not show anything out of the ordinary.
Just saw one where the skirt broke off up within 1/8th inch of the bottom piston ring...showed same compression as the other 5 cylinders. No difference if cylinder was connected to injector or not.
Head was pulled, all the valve tappets were seized from poor oil change intervals...full of sludge. New tappets installed.
Oil pan pulled, rod and piston removed, new piston, rings, and wrist pin, reused connecting rod and bearings.
Oil pump, pickup screen, and tube cleaned.
Customer wanted absolute minimum done. Will be selling..."recent engine work"...60,000 miles 😰 since last oil change, 200,000 mile engine, compression is at 115#, bearings showing wear but no dirt embedded. Engine probably has 30,000 miles left until bearing failure.
@heyinway
So is the answer to my question, "Engine probably has 30,000 miles left until bearing failure." And by that are you saying it will most likely throw the rod at that point?
@heyinway
It's hard to say, if the piston skirt did break off the engine is basically a ticking time bomb. It mainly seems to be an issue with engines made starting in 1996. Some believe that Chrysler starting installing cheaper pistons. If you search out some Jeep forums you'll find more info. Here's a place to start:
https://www.cherokeeforum.com/f2/broken-piston-skirt-181768/