Just picked up a 1999 XJ with 115,000 miles on. This morning I noticed a tick, tick, tick coming from the valve cover area (definately not bottom end). It seems to come and go at all at idle and througout acceleration. Speed of tick increases with engine RPM. It's not a leaking manifold. I picked up a can of rislone to run through it. I'm wondering if it's safe to give it a couple hundred miles to work it's way through or if I should take it in to be looked at right away. I don't know any of the history of this engine.
i am probably wrong, but: when my water pump went out and jeep got real hot i had my head gasket blow. water only in #3, but others dry. i believe the gist of the post i thought i read here was that the 4.0 was more prone to head cracking at one point moreso than others, and would allow water in adjacent cylinders, not just one.
forgive me if my memory is faulty.