Tapping when cold, stops suddenly when engine is warm

[danols15]

Hello,

I have a 1990 Jeep Cherokee, 92000 miles 4.0, Recently, when it was cool outside and I would start it, it would sound fine, but after I started moving, it would begin to tap. it taps faster as you accelerate, slower when you slow down. When I take it on the highway, it runs fine, but taps, I watch the temp guage go up and once it gets to about 200~210 the tapping will just stop. No change in performance. I was wondering if there could be a problem with my water pump impeller and it is tapping the side of the housing, but is dampered when it is full of coolant.

If anyone has had this problem, or has any opinion to give, it is apreciated!

[fredjacksonsan]

"Piston slap" is a common occurrence in the 4.0 engine. Mine does the same before it's warmed up, and is more noticeable in the winter.

There are a few threads about it. I'm not saying there's not another problem but that could be it.

[danols15]

Thank You for your reply!

Does your tapping slowly become un-noticeable when the the engine is warmed up, or does it stop abruptly (loud one second, no noise the next) I thought that Piston Slap could very well be the problem, but I think it is odd that it just stops all of the sudden. I would think that piston slap would slowly become quieter until it was not noticeable.