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Piston slap after MMO and Rotella

88 Wagonman

NAXJA Forum User
Location
Boise, ID
I have always had a little piston slap at idle, no big deal, and I have always run Chevron supreme with a NAPA gold filter. Well, after reading that really long thread about which oil to use, I decided to change to add MMO, use rotella T, and changed to mopar filters, plus I changed my motor mounts and oil filter adapter O-rings at the same time (don't know if it matters, but I'll thow it in there anyway). Well, right afterward I noticed the piston slap getting much louder at idle, and now I can hear it at all rpms! Now that it has been in there for a while it comes and goes, and it is starting to happen less often, even at idle. Any idea WTF is going on? Should I quit using MMO for the next oil change?
 
xjtrailrider said:
Sounds like the MMO may be thinning the oil too much. What grade Rotella did you use?
Well I started out with 15w-40 then it started making noise, so I figured it was too thick, so I drained it 2 days later and put in 5w-40 with only a pint of mmo. (two day old 15w-40 works well in my old ford pickup LOL.)
 
MMO or the Rotella could have cleaned things up too much and removed the caked on crap causing louder slap. Although I'm no engine genius.
 
Jeepm@n said:
MMO or the Rotella could have cleaned things up too much and removed the caked on crap causing louder slap. Although I'm no engine genius.
That had crossed my mind since the engine has like 175k on it and it is a 98 motor (transplanted into renix XJ) which from what I hear is a bad year for piston slap anyway.
 
Sounds like it is cleaning up the old varnish, carbon and wax deposits and some lifters may be sticking and unsticking making the noise come and go. Changing oils or going back to the original oil probably won't help. Best thing is to stay with MMO and Rotella now, change the filter a lot more often at fist, like at 1000 miles or even 500 miles so it does not clog up completely, and let them finish cleaning the crap out of the engine.
 
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