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  #1  
Old January 13th, 2007, 15:16
JeepXJ93 JeepXJ93 is offline
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Piston slap after oil change?

I changed my oil like normal the other day, and now all of a sudden i have noticable piston slap. I searched and read it was common, and from the other 2 XJ's i've owned i figured it was common, but why would this happen after an oil change? I'm using regular 10W-30...it does go away once warm. And when i searched most said its not anything i should worry about...but just for the record, is there a diff. oil i can use or anything to take care of it? Thanks for any additional info.
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Old January 13th, 2007, 16:14
XJPhoenix XJPhoenix is offline
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Re: Piston slap after oil change?

I've had two XJ's, and a few parts XJ's, and all of them clattered like a diesel when first fired up.

I'm no authority, but I have a hunch; thus I am required by post-whore law to state it.

I wonder if it has something to do with the older and dirtier oil gets, the more it gunks up on the cylinder walls, clinging there and quieting the piston slap. Or perhaps it has something to do with newer. slicker oil being so slick that it takes the engine longer to warm up; thus the pistons take longer to 'expand' enough to the point where piston slap goes away. Maybe it's something to do with new detergent & cleaners in the oil cleaning out any gunk in the rings, making them free to rattle about and inducing the relatively harmless rattle we who drive the 4.0 love and cherish.

Or, am I so far off base I need a road map and GPS fix in order to get back?

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  #3  
Old January 13th, 2007, 16:30
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clunk clunk is offline
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Re: Piston slap after oil change?

I'm not sure, but I just changed my oil and my rear main is leaking like a seive--pretty much undrivable now until I have the time to fix it in a few days. No piston slap to speak of..the engine is ridiculously quiet for being the straight 6, but I'd almost take a little piston slap if only my damn rear main would seal itself up, I just don't feel like dealing with it at the moment..
sorry, I'm just bitter haha
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Old January 13th, 2007, 16:41
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8Mud 8Mud is offline
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Re: Piston slap after oil change?

Funny I had the same thing happen, when I switched to a middle premium grade of Castrol. Thought I'd give the XJ a treat and give it a meal of the good stuff. The piston slap got louder and most everything else was noisier. I figured the new stuff was designed for mileage and not adhession. I've since switched back to regular old Castrol bulk oil. I use quality, middle cheap stuff, 10-40 ( for my high mileage motor) and change it often. Believe it or not, oil comes in batches and some are better than others. When I find a good batch, I buy a bunch. Or at least take note of the batch numbers. I have an electric thermometer, a viscosity gage and an adhession gage and occasionally test my oils. The best test is actually to rub various brands and mixes between your fingers (new and used).
I was running synthetic Mobile 1 (for decades in various vehicles and machines), but the quality has gone down and the price has gone up.
Piston slap is often RPM sensitive, a little higher RPM and it goes away. An oil that ahderes well to the cylinder walls, can lower the noise level some.
5-90 once said, the feds made the oil companies lower the adhesion index (additives) for many oils to save fuel or something like that. I'd noticed many top end oils just didn't adhere like they used to.
Additives are a pandoras box. The oil passeges to the the cam bearings and then to the main bearings are pretty darned small. An additive that actually improves adhession, without increasing the viscosity much or worse yet clumping and gumming up the works is advisable. Liquid Moly used to be pretty good stuff, but looks decidedly different than it did many years ago. It used to be almost black and would turn your oil black, but worked good. It left a micron thick coating, that was slicker than oil on all the internals. Worked great in noisey gear boxes and motors that would drain back to much and start up noisy.
I worked for years with pumps, industrial gear boxes and generators. You catch on quick to what works and what doesn't, they often run 24/7.
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  #5  
Old January 13th, 2007, 16:45
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UNCC_99XJ UNCC_99XJ is offline
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Re: Piston slap after oil change?

Quote:
Originally Posted by clunk
I'm not sure, but I just changed my oil and my rear main is leaking like a seive--pretty much undrivable now until I have the time to fix it in a few days. No piston slap to speak of..the engine is ridiculously quiet for being the straight 6, but I'd almost take a little piston slap if only my damn rear main would seal itself up, I just don't feel like dealing with it at the moment..
sorry, I'm just bitter haha
Are you sure it's the rear main? They dont usually just let go like that. Valve cover gasket and oil filter adaptor both mock a rear main leak (both will run down the back of the engine and the bellhousing on the tranny.
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Old January 13th, 2007, 17:45
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Re: Piston slap after oil change?

Quote:
Originally Posted by 99XJSPORT06
Are you sure it's the rear main? They dont usually just let go like that. Valve cover gasket and oil filter adaptor both mock a rear main leak (both will run down the back of the engine and the bellhousing on the tranny.
yeah I have checked and checked again..no dice unfortunately. Back of the VC is bone dry and the adapter isn't leaking a drop.

I jacked it up, crawled under and cleaned the oil off the oil pan and bellhousing..I can visually see it accumulating and dripping right from the main seal area...I know it's weird that it just let loose like that all of a sudden, I can't figure it out. All I can think of is that the older oil was holding enough crap together to keep it from not leaking and the new stuff just wiped it clean..
right now at idle it's dripping around 1 drop every 3 seconds, which is a crazy amount of oil.
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Old January 28th, 2007, 08:41
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MoparRobbie MoparRobbie is offline
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Re: Piston slap after oil change?

Ive got a '89 2.5L MJ, 297 xxx km's on the clock and I use 10w30 Heavy Equipment engine oil. I can't remember the brand but my dad gets it from work. Clatters when first changed, but after that. Runs nice and quiet. Only thing I notice is that if I go over 3500-4000 km's without changing it, I get valvetrain noise, so it gets dumped every 3000-3500 km's. Runs like a dream, its specifically for the gigantic Bulldozers that run in concrete dust 24/7
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  #8  
Old January 28th, 2007, 20:02
XJPhoenix XJPhoenix is offline
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Re: Piston slap after oil change?

Interesting...

I wonder if 'Bob the Oil Guy's' website might have an answer?

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  #9  
Old January 29th, 2007, 08:56
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UNCC_99XJ UNCC_99XJ is offline
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Re: Piston slap after oil change?

Quote:
Originally Posted by clunk
yeah I have checked and checked again..no dice unfortunately. Back of the VC is bone dry and the adapter isn't leaking a drop.

I jacked it up, crawled under and cleaned the oil off the oil pan and bellhousing..I can visually see it accumulating and dripping right from the main seal area...I know it's weird that it just let loose like that all of a sudden, I can't figure it out. All I can think of is that the older oil was holding enough crap together to keep it from not leaking and the new stuff just wiped it clean..
right now at idle it's dripping around 1 drop every 3 seconds, which is a crazy amount of oil.
Interesting....I guess it's possible.....just bad luck maybe?

Its only a matter of time before i replace mine. Already done the VC and filter adaptor...and i got a nice coat of oil on my tranny pan from where it's running down.
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  #10  
Old January 29th, 2007, 12:55
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Re: Piston slap after oil change?

I've found that when I use anything but Kendall 10w-30 in my jeep, the motor makes more noises. Exxon, valvoline, etc all cause my 4.0 to make noise.

Just my observations, no idea why it's the case.
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  #11  
Old January 29th, 2007, 14:11
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87baseomatic 87baseomatic is offline
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Re: Piston slap after oil change?

my 92 has 195k on it and it has the slap only at idle. Ive been running 10w-40 but my last oil change I tried some 15w-40 and it made no difference. The minute I give it gas the noise is gone so I am not to concerned. I have heard alot of 4.0L's with the same noises at idle.
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