Just bought a 2003 E500. I noticed a noise in the engine when it is accelerating under a load. I took it to a dealer and they said that it was piston slap and that new motor mounts should take care of this. I had them install these and it did help but did not eliminate the noise completely. Is this common for this carl?

piston slap fixed with new motor mounts.... ha...

piston slap is when the cylinder walls are ovaled by unusual piston action... that is what GM said about the piston slap issue in my moms GM truck

It could be preignition or maybe even a clogged injector causing a cylinder to lean out and detonate. Try running two quarts of Chevron Techron Concentrate with a full tank of gas. You may have to do it a few times. Make sure you're using 91 octane too, maybe from a different gas station (to rule out bad gas).

When you hear the "slap" you should back off because, if it is preignition or detonation, it's definitely not good for the engine. After running that much Techron, you should consider changing the oil. I don't know if it's true but some people claim that the Techron adversely affects the properties of the motor oil and others say that the deposits get into the oil.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

To correct this.. he was experiencing Knocking.....

All Mercedes Gas engines (well at least modern versions) require 91 octane or Premium fuel....

Ah, yes, knocking makes sense. The motor mounts were probably bad too, just something they found when looking, and bad mounts will make some noise more apparent. Yes, run a good cleaner, I like Techron too. Then make sure you are buying the 91 or better fuel. Yes, it is expensive, but so is your car.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red

If its missing it would throw a code. Did the dealer pull any codes out of the SDS?


Also if the dealer said it was piston slap they are idiots, I would never go back. "Piston slap" is a problem that affects some GM engines. On cold starts they will make noise for a few minutes until they heat up and expand. WTF is this dealer thinking? Did you take it do a GM dealer?

Modern engines won't knock, the computer well sense pre ignition and retard the timing before you hear it. The only difference you will notice running 91 vs 87 is slightly less fuel mileage and maybe power on 87.

It was most likely engine mounts, again if its not throwing codes its not the engine.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

FWIW, there’s an MB Service Bulletin from July 2003, that recommends replacing the engine mounts to cure a “piston slap like sound” on certain V8 powered MB’s. I realize the justncases’ car has the M112 V6, but I’ve fixed many “engine knock” complaints by replacing worn engine/transmission mounts.


Who said the engine was mis-firing?


So GM has the market cornered on piston slap? I’ve replaced dozens of “fitted blocks” (new engine blocks with fitted pistons), over the last few years due to piston slap. By the time the driver hears it, the piston skirts have made a mess out of the cylinder walls.

If anyone has the market cornered on piston slap, it's GM. Sure, others can do it, but GM has a great ability to do it from the factory.

The early V8 engines in the Toyota Tundra's are also notorious for piston slap. It is a widespread problem that owners complain about on the Toyota Tundra forums.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I'm surprised that engine mounts are wearing on a 2003. Has there been a design change?

Also, re: replacing engine blocks - ILUVMILS, are you talking about MB engine blocks?

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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV

Yes, MB engine blocks with fitted pistons and rings.

Any particular models worse than others? V6, V8?

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DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
11 GLK 350 So far, so good
08 E350 4matic, Love it.
99 E320 too rusted, sold
87 260E Donated to Newgate School
www.Newgateschool.org - check it out.
12 Ford Escape, sold, forgotten
87 300D, sold, what a mistake
06 Passat 2.0T, PITA, sold

Las Vegas NV

M112's and M113's.

Why do these engines sometimes need a new block?

Are these early engines (1998-1999) run on conventional motor oil on FSS?

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Interested in this thread.

W210 in my future fading (rust...)...fading (spring perches)...fading...

Maybe I'll just get that 450sel I've wanted for ten years.

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E