Did some searching through the forum, thought I found an answer, but that didn't pan out as well as I had hoped. Just bought a 98 Jeep Grand Cherokee with the 4.0L engine, 86K miles. Didn't have any piston slap/lifter noise when I bought it. I changed the oil a couple days after I bought it with Quaker State High Mileage 5w-30/Fram PH16 filter. Then I had lifter noise. Searched around here yesterday, and then last night I changed it again with Chevron Delo 15w-40. Helped a bit, but I still hear it. Any ideas on what I can add to help quiet the lifter noise? My 91 Cherokee with 200K does it and sounds like a diesel engine its so bad, I don't want this one going that route so soon. Thanks in advance, sorry for the long post.