HELP!!! Weird knocking when engine warm...

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Aug 9, 2010 | 10:26 AM

Tetrylone

Thread Starter

Junior Member

Joined: Jun 2010

Posts: 83

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Model: Cherokee

HELP!!! Weird knocking when engine warm...

Hey all,

I have an 88 Jeep XJ with a new motor in it. Motor has about 300 miles since reman. Sounds nice and quiet on start up and then starts to sound a bit like a diesel when fully warmed up. The sound is a bit louder underneath the vehicle. Mechanic says it's piston slap but everything I've read about piston slap says it's noisy when cold and quiets down when the engine is warm. Anyone got any ideas on this?

The knock is most noticeable during idle and above 1000rpm you can't hear it. Thanks

Last edited by Tetrylone; Aug 9, 2010 at 10:30 AM.

Aug 9, 2010 | 12:18 PM

bigjustice91

Junior Member

Joined: May 2010

Posts: 80

Likes: 0

From: Cross lanes, WV

Year: 1996

Model: Cherokee

Engine: 4.0 inline 6

I don't think it's a piston slap at all. A piston slap would be constant not only just when warm. Since you got a new motor in there, try putting in a thicker oil, like 10W-40 and a small container of STP Oil Treatment to help the motor break in. And if the motor blows, you may have a warranty to fallback on