Piston Slap?

[justncase]

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?

[TheDon]

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

[emerydc8]

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.

[TheDon]

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

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

[crhenkel]

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.

[Hatterasguy]

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.

[ILUVMILS]

Originally Posted by TheDon

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

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.

Originally Posted by Hatterasguy

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

Who said the engine was mis-firing?

Originally Posted by Hatterasguy

....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?

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.

[dlssmith]

Originally Posted by ILUVMILS

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.

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.

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?

[Matt L]

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.

[suginami]

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.

[TheEngineer]

I may be the expert on piston slap: I bought a Subaru Outback 2.5 liter engine (4 cyl boxer) new in 1998. It's an aluminum block with steel liners, so the pistons run on a steel surface. Soon after I bought it, I heard piston slap when the engine was cold in the morning for a few miles until it warms up. The noise also goes away when there is very little load on the engine, like driving downhill. The piston slap re-appears when there is a lot of load on the engine at low rpm. as in towing a trailer uphill. Now the engine is warm. I made big noises to Subaru. They told me:"we know, but it's not detrimental to the longevity of the engine". But the mechanic tells me they have supplied replacement engines free of charge in cases where the piston slap wouldn't go away after driving it a few miles. Now, 10 years later, I have 47,000 miles on the engine, it still makes the noise, but it doesn't use any oil (yet). So, maybe I'm not the expert, but I sure hear it every day. I think, the piston skirt is too short, the piston has a too much clearance and slaps in the cylinder. The aluminum block transmits the noise more than a cast iron block. It's not pre-ignition: That is much louder and scary and happens on acceleration. It's really noticeable even for a dumb engineer. I just did my Honda Trail 90: On a two inch bore I had the shop bore it 1/2 thousand inch larger than the piston. When you do that, the dry piston, without rings, stays in the hole against gravity. I broke it in, in several short high speed, high load runs. We have just the hills here for that. Runs wonderful now. Uses no oil, no smoke.

[dlssmith]

From time to time, I hear what I would describe as piston slap coming from the 99. I hear it when going through the drive through next to a building and the window is open. I don't hear it everytime. In fact most of the time the engine is so quiet you can hardly hear it running.
The thing uses no oil. Runs like a top. Starts just fine, and doesn't necessarily make the noise on start up either.

I've heard real piston slap, in an engine that had to be replaced. A GM product. It's not as bad as that was, but I'm pretty sure, based on this thread that that's what I'm hearing.

[brewtoo]

I assume your engine is at idle when you're in the drive-thru.

More likely to be a valve lifter than piston slap.