I recently purchased a 1993 Jeep Wrangler (having recently sold my 1972 Jeep CJ5) but in bringing it home, I knew that engine maintenance was probably an issue as it was unknown. The engine ran great, but the oil was on the dirtier side, so I got her home and changed all the fluids. I decided to use the recommended 10w-30, five quarts, and I added one quart of Lucas Oil Additive. At startup it purrs, then as she starts to warm I’m getting what I believe to be piston slap...
I agree with your diagnosis, as piston slap is a common issue (TSB 09-08-94) on Jeep 4.0-liter engines from the 1990s. But it’s far from a death sentence, likely more of an annoyance that will occasionally grate at your soul...
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Why isn't piston slap a problem? Seems like if the piston is banging around enough to make a noise, it should be harming the rings and the cylinder walls.
The worst piston slap I ever heard was a 25 year old Golf in Massachusetts that had been driven on a commute of a mile and a half each way for all that time. Belonged to a romance writer of note, who is a friend of some cousins of mine. She subsequently got a Fit, and the Golf was sold to a local with wrenching skills.
We'd all assume the sound would cause significant damage, but it's usually very insignificant. The sheer volume of GM 5.3L Chevy/GMC trucks and SUVs with piston slap prove that owners can continue driving for tens (or hundreds?) of thousands of miles with no decline in performance. Just that annoying noise.