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The Dreaded PISTON SLAP


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14 replies to this topic

#1 Setright

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Posted 21 November 2004 - 02:56 PM

Hi all!

My EJ20 has developed what I believe to be cold start piston slap. It's nearing the 60k milestone. Has anyone had an engine develop piston slap so late?

Funnily, it started when I switched to Redline engine oil. I have since drained that, and re-filled with Mobil 1 again. (5W-50) But it's still slapping and sounding like a Diesel engine in the mornings.

#2 blitz

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Posted 21 November 2004 - 03:52 PM

Mine started slapping very faintly at around 20k, and has been getting a littler louder every winter. It doesn't seem to matter what oil I use, but is rather a function starting temperature.

It doesn't slap immediately at startup, but builds in intensity as the temp gauge climbs toward the "normal" mark, then begins to slowly diminish over the next 2-5 miles (depending on outside temp) as engine heat becomes saturated and uniform.

#3 StapleCheese

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Posted 21 November 2004 - 04:11 PM

Started at 20k? You know you should be able to get that covered under warranty... that is, if you're still under 3/36...

#4 operose

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Posted 21 November 2004 - 04:27 PM

think a block heater would help prevent that? I'd try it if I were you

#5 Commuter

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Posted 21 November 2004 - 07:31 PM

I had a new block (but a Phase I block) put in 2.5 years ago (97 OB). I noticed this fall, after approx. 90k miles, that it is exhibiting some cold piston slap. It had a little right from day one, but very minor. Way way better than the original engine ever was. I'm not sure just when it started, but presumably it has been a slow, gradual progression. Given the time and miles it has taken, I'm not too worried about it. I still worry more about the head gaskets to be honest.

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#6 cookie

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Posted 21 November 2004 - 11:10 PM

within the last year or so seems to have some slap. You are lucky you got 60,000 out of it. 2.2s are definately better. My 2.5 slap has stayed just about the same for the last 20,000 miles, and at 105,000 or so sounds like it will slap on into infinity. At least you don't have to worry about your head gaskets like commuter so relax a bit.

#7 gbhrps

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Posted 21 November 2004 - 11:26 PM

My 97 OBW developed the slap at 23 000 kms and got a little louder over the next winter or two, stablized and never got any worse all the way to trade in time at 234 000 kms. The block heater helped tremendously during winter startups, drastically lowering the noise and length of time that you had to suffer it. I traded up to an 02 OBW that now has 82 000 kms and a little bit of slap. Haven't had to use the block heater yet as temperatures haven't nosedived yet. This new car had the leaking head gaskets (external leaks onto the exhaust manifold) replaced at 46 000 kms, and about 15 000 kms ago had the Subaru recall work done, that adds a special head gasket sealant to the coolant system. Love the car, and knowing that the piston slap issue will just be an annoyance that I can live with, and won't hurt the car, or cost me any money to fix, I'll own another OBW when this one serves its time. In my opinion it really comes down to whether or not you can live with the annoying noise or not. I'll accept it because everything else about these cars is so darn good.

#8 Setright

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Posted 22 November 2004 - 01:12 AM

Thanks guys! Your stories give me peace of mind. I was in a "worry-spiral" about it yesterday because frost is setting in, and the noise is of course louder.

#9 blitz

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Posted 22 November 2004 - 10:35 AM

Started at 20k? You know you should be able to get that covered under warranty... that is, if you're still under 3/36...


Well... I really have two choices:

1. I can remain productive by pretending the slap isn't there.
2. I can put my life on hold while the dealer pretends the slap isn't there.

I'm fairly certain that the moly coating on the piston skirts is in place primarily to keep the slapping noise down during the period that the finance institution owns the vehicle, but it wears off rather quickly. The slapping motion of the piston which is a function of piston dimensions, to wit:

1. Short skirts.
2. High ring-pack position.
3. High wrist-pin position.
4. Barrel shape.

is actually occurring from day one, albeit just not audible.

#10 friendly_jacek

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Posted 22 November 2004 - 11:09 AM

This just shows you how short skirts could be dangerous...

But seriously, I heard that Castrol's start-up blend oil helps in some cases of slap (posted on BITOG). Did you experiment with different types of oils? Some oils have moly additives.

#11 blitz

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Posted 22 November 2004 - 04:43 PM

This just shows you how short skirts could be dangerous...


LOL!!! :lol: :banana: :lol: :banana: :lol: :banana:

But seriously, I heard that Castrol's start-up blend oil helps in some cases of slap (posted on BITOG). Did you experiment with different types of oils? Some oils have moly additives.


I do lurk a bit on BITOG and I've seen the comments about moly-containing oils tending to help the slap, but I haven't experimented. I'd like to try some Schaeffer's, but it's not available retail.

#12 canedog18

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Posted 24 November 2004 - 07:12 PM

My '97 Outback has had the slap since about 60k or so, right after I bought it used. It had the cold weather package and I garage it at night and plug in the block heater when the temp drops in to the 40's. I have noticed that the block heater helps with piston slap to some degree. I don't know if it makes much difference but I try and plug it in right after I get home from work while the engine is already warm, thinking that maybe it will be a touch warmer in the AM.

#13 Setright

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Posted 25 November 2004 - 01:53 AM

Yeah, but I park on the street, and I don't want to pay for a gasoline driven engine heater. Also, I don't want someone fiddling with my fuel and coolant systems to install the thing.

Piston slap will surely be less, but the pistons run much hotter than any engine heater. I wish I had a house and a garage.

#14 canedog18

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Posted 25 November 2004 - 05:37 PM

I wish I owned my house and garage, but I rent it !! I remeber places like JC Whitney used to sell engine blankets. I have no idea how effective they are and it sure would be a minor hassle going under the hood at least twice a day. I may try that castol start up oil as my oil is due for a change, but I have a feeling it's more of a gimmink than anything else.

#15 blitz

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Posted 26 November 2004 - 08:26 AM

canedog, the engine blankets are designed to be used in conjunction with a block or pan heater to help hold in the heat generated by the engine heating device, especially if the vehicle is out in the wind.

The blanket could also be used to retain a greater degree of engine heat for a short period after being driven.




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