Piston Slap?
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This is a discussion on Piston Slap? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Recently I brought my completely stock 02 WRX in for service because I was hearing a knocking noise coming from ...

  1. #1
    Registered User turbo022's Avatar
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    Piston Slap?

    Recently I brought my completely stock 02 WRX in for service because I was hearing a knocking noise coming from the engine on cold startup. The noise was intermittent and would go away after the engine was warmed up. I took the car in and the timing belt tensioner was replaced. The next morning I still had the same noise. So I left it at the dealer overnight and in the morning I met with the tech and the service manager to "listen" to the engine. I was told that the problem was piston slap, and that they werent going to do anything about it because it only did it when the engine was cold, and that this was "normal" for this engine. I personally thought this was a load of BS, so I called a Subaru specialist in my area and asked them about it. They confirmed my BS assumtion. Now I am stuck trying to contact SOA so I can get a new shortblock put in. Man I hate this crap. I love the car but have had nothing but hassels with it. I had it in 3 times because the dealership couldnt seem to find the leaky axel seal in the transmission even though I told them where it was leaking each time I brought it in. Not to mention the 4 days I had to wait so they could repaint the hood because the paint was peeling off. I am sick and tired of this crap. I hope that Subaru is going to stand behind their product and replace my engine. I am interested to see how "normal" this is. Dont worry I know they are feeding me a line of BS. Piston slap is never normal. So please say wheter or not you have this problem.

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  3. #2
    Registered User SilverX's Avatar
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    This isn't what you want to hear but it is a normal phenomenon for subaru engines. I believe there should be a blurb about it in your manual. I get it every now and then at cold start.
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    Registered User turbo022's Avatar
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    Mine isnt really every now and then. It is more like every single time the engine is cold started.

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    Registered User chevyeater's Avatar
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    Wow. That sucks. Sounds like you got a noisy one.

    I work for chevy and we have the same piston slap deal on the 3.1 V6. GM says it is normal too but gives customers the opportunity to replace the pistons with updated polymer coated ones. It is the short skirt piston design, if the clearance is a bit on the loose side they slap. They can scuff the cylinder walls and cause damage but, only in extreme cases.
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    Registered User BoostedBoxer's Avatar
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    not sure if our pistons have a high silicon content but if they do, then they expand when hot. So, when they are cold, they are smaller and take up less of the bore. Its okay and very common in high performance engines.
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    Registered User KanosWRX's Avatar
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    Yeah, I have been reading these fourms for over a year and everything I have heard says its normal. Even the subaru tech magazine The End Wrench says its normal. I wouldn't worry to much about it unless it happens when the car is at normal operating temp.


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    Registered User WRXin''s Avatar
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    Hmmm....I've never heard of this ever! Could it be because of where you all that have experienced this live? It doesn't get quite as cold here as does up north...could that be part of the problem? If so, I got an extra futon
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    I have not heard the sound, but most engines will make some ticking\knocking sound when it's cold. Probatly many reasons why, one thing I have heard is that the engine oil don't flow that well when it's cold (oil is more "stiffer" if you know what I mean)

    So when the oil is cold it don't protect the engine head (valves and lifters) that well. This is one of many reasons you should never drive your car hard before it warms up..

    Hope this helps
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    Registered User turbo022's Avatar
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    Well last night here in Denver the ouside air was around 35 degrees. When I sarted the car the piston slap noise was signifigantly louder than it has previously been. Now even when the engine is warmed up the noise will not go away. So I guess it is back to the dealership so they can put in a new short block .... oh well. I will have to call them tomorrow and see what they say. Ill keep you all posted.

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    Registered User wrx420's Avatar
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    Good luck, cuz they're not gonna give you a new short block. If it stops making the noise after the car warms up, it's just normal operating parameters for the engine.. Mine does it too a little when cold.

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    Registered User mourning_air's Avatar
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    I have had this happen once on my WRX, and it was after a cold night and not driving the car for a day. This used to happen every time I started my maxima, i30, and pathfinder so I wasn't too concerned. If it doesn't go away when warm like you say, then it probably is best to take it in.
    What oil and weight do you use? whens the last time you changed it and have you checked the level lately?
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    Registered User turbo022's Avatar
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    I always use 5w30 weight oil. I have changed it recently and I checked it this morning and it was 1/4 quart low after 300 miles after an oil change. So I guess we will see what happens tomorrow.

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    Registered User mourning_air's Avatar
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    Out of curiosity, what dealership are you going to?
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    Registered User turbo022's Avatar
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    I have been taking it to Burt Subaru in Littleton. They said if the problem got worse or if it did not go away oafter warm up then they would replace the short block.

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    Burt??


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    Registered User mourning_air's Avatar
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    Originally posted by djrez4
    Flatirons!! Flatirons!! Flatirons!!
    Agreed, or Mike Shaw.....
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    So does piston slap affect performance?

  19. #18
    Registered User WRXin''s Avatar
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    Originally posted by SilvaWRX
    So does piston slap affect performance?
    Since they're saying it's normal, I presume it doesn't
    Fahd

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  20. #19
    Registered User KanosWRX's Avatar
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    When you do get piston slap when the car is cold you should not be pushing your car hard. You should let it warm up before going past 4k rpms. Just look at the M3, it has an electronic tach that changes the redline from cold start to fully warmed up. I think the M3 shows a redline of 4k rpm when cold, then as it warms up it slowly raises the redline. I usually let my car idle for 30 sec to 1 min in the morning, then drive around slowly until it reaches normal operating temps.


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  21. #20
    Registered User WRXin''s Avatar
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    Originally posted by KanosWRX
    Just look at the M3, it has an electronic tach that changes the redline from cold start to fully warmed up. I think the M3 shows a redline of 4k rpm when cold, then as it warms up it slowly raises the redline. I usually let my car idle for 30 sec to 1 min in the morning, then drive around slowly until it reaches normal operating temps.
    That is a cool thing that the M3 has! I do the same thing in the morning as well. You can feel the car isn't running at optimum level when it's still cold.
    Fahd

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