Experimenting with oil viscosities

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So... I have a. '03 Subaru Forester 2.5x. I'm the second owner, vehicle has 113k on it and I've had it since 95k. Pretty clear that the previous owner didn't take very good care of it. Anyways... Subaru piston slap. Sounds god awful when it's cold. And I'm really not exaggerating when I say it sounds like a diesel sometimes. Goes away when it warmed up. Engine doesn't use any measurable amount of oil between oil changes, nor does it leak. I've tried using 5w-30 synthetic oil. Valvoline synpower. The cold piston slap nearly went away after about 800mi of driving with a bottle of MoS2 in the oil and enough ZDDPlus to bring the phosphorous concentration up to 1400ppm. So fast forward to the next oil change. I decided to try something a little bit thicker to see. Rotella T6. Once again, with a bottle of MoS2 and enough ZDDPlus to boost the phosphorous levels. It seems like the piston slap got louder after switching to something a bit thicker. No notable difference when warm, but it sounded pretty lackluster when the motor was cold. So now... I'm considering trying something that's a bit thinner when cold. Perhaps a 0w-30 oil to see if that makes any difference. I'm a bit leary of going below a 30 weight oil - or even a mix of 30 and 20, for fear of losing oil pressure when warm. So yeah there's my brain dump. Thoughts/opinions/warnings/berations? I'm in the pacific NW. Not really much in the way of extreme temperatures either way. Most summer days are 90 degrees on the warm side, anything above 100 is a rarity. Winter nights are generally between 20 and 25, with 45 or so temps during the day. Single digits for maybe 1 night out of the year
 
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What is the factory piston clearance? If it is .003" or more the piston slap is going to be audible and is not something a lubricant is going to change. Smart, or should I say experienced engine builders like everything on the loose side. Especially with performance engines where crank and block flexing and harmonics can change static clearances.
 
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People have reported Pennzoil and Quaker State dino have cured noisy engines (I'm guessing the dino base oils plus the high moly content?). You could always give one of those a try and see what happens.
 

SnowDrifter

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Not sure about clearance, but as I understand it, it's more or less a design flaw with these motors due to then having very short piston skirts, allowing them to rock a little bit. Everywhere I can read says it's not an issue for the longevity of the engine, but that doesn't make it any more pleasant to listen to
 

SnowDrifter

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Could you expand on this Dino base oil thing? How does base stock relate to noise? What changes?
 
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Try Red Line 0w-30. It already has higher levels of moly and ZDDP so you won't need to add anything.
 
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Originally Posted By: SnowDrifter
Could you expand on this Dino base oil thing? How does base stock relate to noise? What changes?
If conventional oil makes an engine quieter, some speculate that it's because of molecule size. Molecules in conventional oil are less-consistent in size and shape than synthetics so, the theory goes, some larger than normal molecules may cushion things a bit more and result in a quieter engine. Does this happen and is this the reason? And even if so, would it help with piston slap? Don't know, but it would be a pretty inexpensive experiment to try.
 
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Originally Posted By: Danh
Originally Posted By: SnowDrifter
Could you expand on this Dino base oil thing? How does base stock relate to noise? What changes?
If conventional oil makes an engine quieter, some speculate that it's because of molecule size. Molecules in conventional oil are less-consistent in size and shape than synthetics so, the theory goes, some larger than normal molecules may cushion things a bit more and result in a quieter engine. Does this happen and is this the reason? And even if so, would it help with piston slap? Don't know, but it would be a pretty inexpensive experiment to try.
^^This. A member also explained it in this way,conventional (dino) oil's molecules are various shapes and sizes vs synth's uniform shapes and sizes,therefore the conventional oil's molecules will fill in the spaces of a metal's un-uniformed surface,reducing the mechanical noise. His theory sounds like a great layman's theory which finally made me understand the noisy engine phenomenon.
 
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Layman's theory is beautiful. You can support it or pick it apart. Typing this under an apple tree...while another meaningless apple falls wink So, maybe I should mix a quart of 6 different-base oils for my next 6qt OCI? Or maybe try different colloidals? graphite, ptfe, ws2, boron, calcium, moly, graphene, ....?? shaken or stirred? Try the alphabetical list of oils. If you find one that quiets the clatter, stick with it.
 

SnowDrifter

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The oil cap dictates 5w-30. But the owners manual essentially says you can use from 5w-30 up through 20w-50. That's why I was a bit cautious on going with a thinner oil. I suppose without a UOA to determine wear metals it's nothing but a "feeling"
 
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Originally Posted By: SnowDrifter
The oil cap dictates 5w-30. But the owners manual essentially says you can use from 5w-30 up through 20w-50. That's why I was a bit cautious on going with a thinner oil. I suppose without a UOA to determine wear metals it's nothing but a "feeling"
And even with wear metals it's nothing but a feeling until you've established trends in all the columns. Wear can only be measured by tearing down an engine and measuring the parts at build time and tear down and comparing the 2. A used oil analysis is NOT an accurate method of determining wear in an engine,so please get it straight. Yes once trends are established anomalies can indicate problems,or theyay indicate a particle streak,which is why a tear down is required. We've had used oil analysis posted here that looked stellar and the engines grenaded and we've had used oil analysis that show serious high levels of "wear metals" than we running just fine at the time of sale,write off or when scrapped. Keep that in mind when putting all that faith in a 30 dollar used oil analysis. They are done to check the condition of the oil,not the equipment the oil is in. Just sayin.
 
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I am a big fan of Maxlife It is a little thicker when hot so why not give 5-30 a try?it sure wont hurt anything
 
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Quote:
Subaru piston slap. Sounds god awful when it's cold. ... Goes away when it warmed up.
So warm it up easy with your radio turned up louder. The noise is mechanical. It won't go away by you spending money on snake oil.
 
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I've been listening to piston slap in my LS1 Camaro since 2002, and have not yet found the oil that makes it go away. What I found in my last oil change going from German Castrol to PU/PUE mix, was less piston slap. It seems lower viscosity decreases piston slap in my case. When you hear cold piston slap, have you ever tried gently revving the engine to see if it goes away? I do this with my Camaro on cold mornings, and the piston slap goes away at 1700 rpm. Then when the engine gets up to operating temperature, it's good at 800 rpm idle. (Except on GC, though, the engine still had piston slap at idle when fully warmed up.)
 
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SnowDrifter

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Quickie update for everyone. I tried some 0w-20 in the Subie. No filter change, just drain and fill. Sounded no different than 5w-30 when cold, but never really went away when warm. At that point I decided that's it I'm done. Tossed a can of STP in there to thicken it up a bit 'till I got home. Planning on doing my real oil change with some 0w-40. Even if it does sound like a diesel sewing machine when cold, it's quiet when warm and doesn't use oil. Anyhoo... That was a fun little experiment. Even if it didn't turn out like I wanted in my head, it's good info to know at least
 
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Originally Posted By: SnowDrifter
Quickie update for everyone. I tried some 0w-20 in the Subie. No filter change, just drain and fill. Sounded no different than 5w-30 when cold, but never really went away when warm. At that point I decided that's it I'm done. Tossed a can of STP in there to thicken it up a bit 'till I got home. Planning on doing my real oil change with some 0w-40. Even if it does sound like a diesel sewing machine when cold, it's quiet when warm and doesn't use oil. Anyhoo... That was a fun little experiment. Even if it didn't turn out like I wanted in my head, it's good info to know at least
Thanks for posting up...and volunteering your Subaru for the test. grin
 
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Yeah, IMO nothing will likely help. My wife had a '99 Outback with Genuine Subaru Piston Slap and I tried various 0/5/10W-30's and various 5/10W-40's, conventionals, blends, and synthetics and nothing made a difference. The head tech at my dealership said that Subaru came out with larger pistons for that series EJ engine. -Dennis
 
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