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Best oil viscosity for piston slap?


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20 replies to this topic

#1 bdecriscio

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Posted 11 September 2009 - 08:33 PM

My 99 Outback(103 thosand miles) has developed what I think is piston slap,knocking on startup, quiets down almost immediatly . Older posts seem to be a bit confusing. Some people suggest a lighter viscosity, other posts suggest heavier ones. I prefer 10-40 for all season here in central Pa. But that might be wrong for this condition. I'm assuming the lighter oil flows faster at startup and heavier oil would dampen or adhere better but I'm not knowledgeable enough to know which would help with piston slap. Any advice is appreciated. Bob

#2 grossgary

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Posted 11 September 2009 - 10:07 PM

the reason you can't find an answer is that you can't fix or mitigate a problem with something that doesn't fix the problem. it's kind of like "how much air pressure do i need in my tires to fix my wheel bearings?"

that's a crude analogy but even still, piston slap is not fixed by oil viscosity. try a few different weights and see what you like. if there's a particular weight that helps your car then go with it, but there's no "one size fits all" solution here except to replace the piston(s).

#3 Fairtax4me

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Posted 11 September 2009 - 11:17 PM

Might try a new oil filter. The anti drain back valve may be faulty and is causing whats called a "dry start". Basically means there's no oil pressure in the valve train for a few seconds after starting. Once the pump gets oil to the rockers and the pressure builds the noise goes away. It's not necessarily bad, but it's not good either.

#4 bdecriscio

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Posted 12 September 2009 - 09:04 AM

Thanks for the replys, I guess I knew that the oil differences would't fix the problem but still not clear if the piston slap causes any damage and if so would any type of oil help mitigate the problem. I think I will change the filter as well since I'm thinking it's a possible dry start up scenario. Bob

#5 johnceggleston

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Posted 12 September 2009 - 09:41 AM

still not clear if the piston slap causes any damage


i bought a 97 obw for cheap with 98k miles which had a "bad wrist pin". seller said it needed a rebuild. it turned out to be piston slap. i've been driving it for 30k miles now with no indication of a problem. i suspect HGs will get me before piston slap does. i can't see putting new HGs on an engine with piston slap , but we'll see.

from a bulletin i read when doing my research at the time of purchase, "it is not a sign of iminent failure". of course that does not speak to damage it may cause after 100k miles.

#6 grossgary

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Posted 12 September 2009 - 11:07 AM

piston slap is not a problem if you can tolerate it - turn the radio up! there's no worries about future failure, reliability, or break down.

#7 Rooster2

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Posted 12 September 2009 - 12:12 PM

Like others have written, I have heard that piston slap doesn't cause any damage, just sounds bad. Just sounds worse then really is.

On my 99 Subie, I use 20-50W oil in the summer, switching to 10-40W in the winter for here in Indiana. Years back a mechanic suggested this for any car with more then 100K miles on the odo. I have followed his advise for years, and have been happy with the results.

#8 bdecriscio

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Posted 12 September 2009 - 12:53 PM

Great advise from all, thanks, Bob

#9 davebugs

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Posted 13 September 2009 - 03:39 PM

Hey - if it only lasts a few seconds are you sure it's not the oil pump/backing screws?

Piston slap seems to last several minutes, not seconds.

#10 OB99W

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Posted 13 September 2009 - 05:32 PM

Piston slap is a sound generated when the piston has excessive clearance in the cylinder bore. Generally, as the engine warms and expansion occurs, the noise diminishes. As davebugs said, that wouldn't typically be audible for just a few seconds, but rather minutes.

For info on what's ''normal'' and what isn't, see http://endwrench.com...s/OtherInfo.pdf .

#11 bdecriscio

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Posted 13 September 2009 - 06:26 PM

You guys may be right, My noise does go away almost instantly, at most a few seconds, I'll do some research on the oil pump/ backing screws. Any advice on that direction is also very appreciated. Bob

#12 Olnick

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Posted 14 September 2009 - 01:39 AM

Bob, the oil pump/backing screws are usually done in conjunction with a timing belt job since you have to go into the engine's front end for both.

Have you replaced the timing belt recently? At 103k miles it's about due.

Are you sure it's knock that you're hearing--or could it be valves ticking?

#13 bdecriscio

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Posted 14 September 2009 - 07:46 AM

Hi Olnick, I have had the timing belt replaced about 6000 miles ago but I'm pretty sure the mechanic didn't do what should have been done with the oil pump. As for the noise, I really am not sure what it is. I thought from my reading of other posts that my engine doesn't have adjustable valves so I went on the asumption it was piston slap. Again, not knowing that that behavior doesn't fit either. I guess a little bit of knowledge is a dangerous thing. Anyway, to recap my sounds, pretty loud low tone knock on startup not really a chatter sound, goes away quite quickly, but this might be helpful, it does it even on a warm engine after setting for more than say 15 minutes. The car runs very well, very little engine noise when running or idleing, sometimes can hear a bit of what I would perceive as valve noise but not really noticable unless listening for it. As always I appreciate the forums elp with problems. If it is the oil pump issue, do I need to act quickly or is it more of an annoyance issue versus wear and tear? Thanks again, Bob

#14 davebugs

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Posted 14 September 2009 - 07:54 AM

Sounds oil pressure related to me. Pump is most suspect but could also be Oring on the pickup tube.

When I say it sounds like the pump usually they do not need replaced but just the backing screws tightened. But if I were paying someone to do the job I may just install a new one.

If things like crank/cam seals weren't done at TB job time I'd consider them, possible idlers and possible WP. The engine will be have to be torn down to a level where they wouldn't be much more labor - just $'s for parts.

#15 Olnick

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Posted 14 September 2009 - 01:55 PM

You're probably right about the valve tick, Bob. I admit I'm stuck in the early EJ22 era!

I'm not an "engine internals expert" enough to be much help, but I agree with davebugs--it would seem to be a low oil pressure problem. Hopefully others will chime in too.

Sounds like your mechanic just slapped a new belt on and maybe skipped some vital inspections and PM. Now all that front end work would have to be repeated to get to the oil pump.

Have you noticed any excessive oil leakage from the timing belt cover? How's your oil level, does it use much?

Wonder if it could be some kind of blockage in the oil passages? Someone correct me if I'm wrong--but maybe a treatment with MMR (Marvel Mystery Oil) could help?

Good luck Bob.

#16 bdecriscio

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Posted 14 September 2009 - 03:10 PM

I,m sure you are right about the mechanic missing some common sense preventive mait. when he did the timing belt. I did know enough to have him replace the cam seals since I had leakage at the cover but it still leaks a bit there so I'm not 100% sure if they just failed as I'v read sometime happens or if he did it wrong or not at all(don't think so). I do have a leak at the rear but total all my leaks probably amount to about 1/2 quart between oil changes. Maybe some more input form the forum and then as Davebugs suggest do a lot of internal maintenance at one time. Thanks, Bob

#17 OB99W

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Posted 14 September 2009 - 03:33 PM

[...] I did know enough to have him replace the cam seals since I had leakage at the cover but it still leaks a bit there so I'm not 100% sure if they just failed as I'v read sometime happens or if he did it wrong or not at all(don't think so). [...]

If you have leakage at the crank seal, it might be due to the oil pump problem previously mentioned.
See http://endwrench.com...ngFrontInfo.pdf .

#18 bdecriscio

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Posted 17 September 2009 - 07:47 AM

Hi all, Frankly a little embaressed to say I've got bad bearing in my engine. Confirmed by sound by two mechanics I trust. I know the best direction from here is a 2.2 replacement engine but short term if I put heavy oil in and drive conservativly, can I get by for days, weeks months? I did put a new filter on that quieted the initial knock and the overall bearing noise is not really very loud if that helps. I guess as I speak, maybe I was getting a dry start due to a bad filter that could have contributed to the issue. Thanks for all those who have posted. Bob

#19 grossgary

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Posted 17 September 2009 - 07:53 AM

knocking on startup, quiets down almost immediatly .

that sounds like piston slap.

plenty of mechanics have misdiagnosed piston slap and called it "bad bearings". i wouldn't necessarily think he's right.

i bought a Subaru wagon with "bad bearings" within the past year from a "subaru specialist", it wasn't bad bearings, it's piston slap. wasn't even that bad of piston slap actually, i've heard much worse.

#20 davebugs

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Posted 17 September 2009 - 07:56 AM

that sounds like piston slap.

plenty of mechanics have misdiagnosed piston slap and called it "bad bearings". i wouldn't necessarily think he's right.

i bought a Subaru wagon with "bad bearings" within the past year from a "subaru specialist", it wasn't bad bearings, it's piston slap. wasn't even that bad of piston slap actually, i've heard much worse.



Hope you don't mean the one I sold you that needed HG's or an engine - I forget. Then again I really didn't spend much time on it or I would have fixed and sold it myself.

#21 johnceggleston

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Posted 17 September 2009 - 08:13 AM

i found this when researching piston slap and found it helpful. especially the plug wire part for checking a 'knock'.

http://remanufacture...s.com/page4.htm

i bought my piston slap 2.5 subaru with a bad "wrist pin". still slappin' 30k later. so buy a AAA membership and drive it until it quits. THEN have it towed and replaced.




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