interesting paper on piston slap noise
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Originally Posted By: Samilcar
I've been using 5W-20 in our 2GR-FE engined 2008 Sienna for the last 38,000 miles with no piston slap either then or now.
There are 3 potential explanations for the variance:
1. Your engine has closer piston/liner clearance
2. Your piston skirt coatings are not worn down yet
3. The way you drive you don't accelerate 1500-2000 RPM up hill in the first mile of driving or you don't listen to engine
I don't know which applies.
I've been using 5W-20 in our 2GR-FE engined 2008 Sienna for the last 38,000 miles with no piston slap either then or now.
There are 3 potential explanations for the variance:
1. Your engine has closer piston/liner clearance
2. Your piston skirt coatings are not worn down yet
3. The way you drive you don't accelerate 1500-2000 RPM up hill in the first mile of driving or you don't listen to engine
I don't know which applies.
usually the coating is a teflon type material. Most mfgrs do not share that info.
I think if you have piston slap that it showed up after a run with 5W20 and is now hanging around is probably coincidental. The piston slap was bound to show up even had 5W30 or 10W30 always been used. Now, using 5W-10W30 maybe will make it quieter. There seems no evidence that the piston slap effects engine wear. A lot older GM engines had piston slap ran only on 5W30 and went on to have a long engine life.
True, but there is another guy on lexus forum who had the exact experience. Yes, it could be a coincidence too, but combined with the paper I linked, I don't think so.
I didn't read that whole paper. Does it say that a thin oil can cause piston slap or just not damping the noise from piston slap as well as other oil grades? I believe different grades of oil can damp or not damp piston slap and other engne noise, but wouldn't think a short run of 5W20 could be the cause of piston slap permanently developing.
That RAV4 does sound like piston slap to me. My CR-V does that as well when cold. Being a 4-cylinder vs. your V-6, the note and tone is different, but it's the same idea. Mine sounds more like a clack-clack-clack whereas yours sound more like a dull hollow sound, but it's also hard to know if that's an artifact of the microphone on your camera.
The fact that it goes away after warm (it does, right?) tells me that this is certainly some type of a clearance issue. I have also noticed that oil selection has an impact on this noise that I hear (at least in my car). I have not used any 30 grade oils, but I have used 5W-20 and 0W-20. The Mobil 1 0W-20 was the quietest in the dead of winter, but I think the Valvoline MaxLife NextGen that I have in it now may be even quieter. I couldn't tell for sure, though, because hasn't been cold since I've had the Valvoline in. Quite the opposite really (supposed to break all-time record highs today at about 106*F).
I have personally found that oils higher in molybdenum help this noise. I also had a Nissan KA24E that would get a little clackity at colder temperatures before it warmed up and a high moly oil (then, Havoline) really helped. In your RAV4, I might first try Pennzoil YB in the correct grade and see if that makes any difference. If not, move up to 5W-30 and see if that helps. That might confirm or dispute the notion that moly and/or viscosity grade makes at difference, at least in your noise.
The fact that it goes away after warm (it does, right?) tells me that this is certainly some type of a clearance issue. I have also noticed that oil selection has an impact on this noise that I hear (at least in my car). I have not used any 30 grade oils, but I have used 5W-20 and 0W-20. The Mobil 1 0W-20 was the quietest in the dead of winter, but I think the Valvoline MaxLife NextGen that I have in it now may be even quieter. I couldn't tell for sure, though, because hasn't been cold since I've had the Valvoline in. Quite the opposite really (supposed to break all-time record highs today at about 106*F).
I have personally found that oils higher in molybdenum help this noise. I also had a Nissan KA24E that would get a little clackity at colder temperatures before it warmed up and a high moly oil (then, Havoline) really helped. In your RAV4, I might first try Pennzoil YB in the correct grade and see if that makes any difference. If not, move up to 5W-30 and see if that helps. That might confirm or dispute the notion that moly and/or viscosity grade makes at difference, at least in your noise.
I skimmed through the article and it was very interesting. It found that increasing cylinder liner temperature (and thusly, the clearance between the liner and the piston skirt) also increased the noise. In the field, it's commonly noted that cold engine slap is worse, likely due to the cold (and smaller) piston itself. The piston in a production engine expands more than the cylinder or cylinder liner, filling that gap in clearance.
I don't know how the conclusions of this study can be related to cold-engine slap that is sometimes heard with certain engine designs. The study seemed to be looking at how various factors affected hot-engine slap; in this case, oil viscosity did seem to help. But how does oil viscosity factor into cold-engine slap? Does it affect it the same? I'm not sure it would, or at least I'm not sure it would *consistently*.
I don't know how the conclusions of this study can be related to cold-engine slap that is sometimes heard with certain engine designs. The study seemed to be looking at how various factors affected hot-engine slap; in this case, oil viscosity did seem to help. But how does oil viscosity factor into cold-engine slap? Does it affect it the same? I'm not sure it would, or at least I'm not sure it would *consistently*.
Originally Posted By: Samilcar
What are piston skirts "coated" with that could wear down?
Quote:
The demand for more powerful internal combustion engines with lower weight, reduced fuel consumption, and favorable environmental properties has led to engine piston designs having lower weight, reduced thermal expansion, and good thermal conductivity. These improvements were needed without sacrificing high thermal strength, reduced operating friction, and increased wear resistance. The need for reduced frictional properties resulted in pistons with shorter skirt lengths, which led to a reduction in effective hydrodynamic surface area perpendicular to the pin bore. At the same time, complex cold start cycles and fuel injection systems were developed that brought enriched fuel mixtures into the engine, causing a dramatic reduction in the viscosity of the lubricant film and thereby its capabilities to protect the sliding surfaces from wear. These higher mechanical stresses on the piston combined with the reduced lubricating ability of the oil film led to increased friction and wear rates, which often resulted in decreased customer satisfaction due to high noise (i.e., piston “slap”) or complete engine failure. To counteract these tribological problems, a variety of piston coatings were developed, but the composition of these coatings often brought a new set of environmental concerns, e.g., the use of heavy metals. The current solution for this problem is to utilize Anti-friction Coatings (AFC's) on specific areas of the piston. These coatings are based on solid lubricant technology combined with that of high performance resins. The coatings are resistant to fuels and engine oils over the normal operating temperature range of the engine. They also provide a long-term lubricant coating with exceptional capability to handle intermittent excursions outside an engine's normal duty cycle.
http://asmedl.org/getabs/servlet/GetabsS...=yes&ref=no
What are piston skirts "coated" with that could wear down?
Quote:
The demand for more powerful internal combustion engines with lower weight, reduced fuel consumption, and favorable environmental properties has led to engine piston designs having lower weight, reduced thermal expansion, and good thermal conductivity. These improvements were needed without sacrificing high thermal strength, reduced operating friction, and increased wear resistance. The need for reduced frictional properties resulted in pistons with shorter skirt lengths, which led to a reduction in effective hydrodynamic surface area perpendicular to the pin bore. At the same time, complex cold start cycles and fuel injection systems were developed that brought enriched fuel mixtures into the engine, causing a dramatic reduction in the viscosity of the lubricant film and thereby its capabilities to protect the sliding surfaces from wear. These higher mechanical stresses on the piston combined with the reduced lubricating ability of the oil film led to increased friction and wear rates, which often resulted in decreased customer satisfaction due to high noise (i.e., piston “slap”) or complete engine failure. To counteract these tribological problems, a variety of piston coatings were developed, but the composition of these coatings often brought a new set of environmental concerns, e.g., the use of heavy metals. The current solution for this problem is to utilize Anti-friction Coatings (AFC's) on specific areas of the piston. These coatings are based on solid lubricant technology combined with that of high performance resins. The coatings are resistant to fuels and engine oils over the normal operating temperature range of the engine. They also provide a long-term lubricant coating with exceptional capability to handle intermittent excursions outside an engine's normal duty cycle.
http://asmedl.org/getabs/servlet/GetabsS...=yes&ref=no
I've seen a lot of explanations for cold start-up engine knock, but this is the first time I've seen a reference to VVTi delayed valve closing:
"It has nothing to do with the pistons, it's the exhaust valve timing from the VVT-I.
When cold, it's modified to keep the valves closed fractions of a second longer.
That's the noise you hear, and it's 100% designed that way.
Stop worrying about it....it's NOT piston slap.
Sounds like some techs need to read their 5.7 white papers a little more thoroughly."
Taken from a tundrasolutions.com thread.
"It has nothing to do with the pistons, it's the exhaust valve timing from the VVT-I.
When cold, it's modified to keep the valves closed fractions of a second longer.
That's the noise you hear, and it's 100% designed that way.
Stop worrying about it....it's NOT piston slap.
Sounds like some techs need to read their 5.7 white papers a little more thoroughly."
Taken from a tundrasolutions.com thread.
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Interesting post. It's news to me but i doubt this explanation (even if it's true), as I had no knock for 37,000 miles and then it suddenly appeared.
I'm convinced it's a tolerance and/or wear issue (as my quotation couple of posts above states it clearly).
I'm convinced it's a tolerance and/or wear issue (as my quotation couple of posts above states it clearly).
I drove my sister in law's 2008 Highlander with a 2GR-FE and 48,300 miles this morning and it had some noises/knocks for about the first mile or so. I'm certain it has seen only 20 grade engine oils since she bought it (serviced by her dealer).
My wife's 2009 RAV4 that saw only 5W-30 and 10W-30 engine oils other than the factory fill had no start-up noises/knocks at all for 43,500 miles. I did all the engine oil changes myself.
Not sure if that means anything, but I thought I'd add it to the discussion.
My wife's 2009 RAV4 that saw only 5W-30 and 10W-30 engine oils other than the factory fill had no start-up noises/knocks at all for 43,500 miles. I did all the engine oil changes myself.
Not sure if that means anything, but I thought I'd add it to the discussion.
Originally Posted By: friendly_jacek
Interesting post. It's news to me but i doubt this explanation (even if it's true), as I had no knock for 37,000 miles and then it suddenly appeared.
I'm convinced it's a tolerance and/or wear issue (as my quotation couple of posts above states it clearly).
If it suddenly appeared that makes piston slap a very unlikely cause. It should have been there from new. You would have to be terribly abusive to wear out an engine in 37k miles!
I'd check that fancy valve gear.
Interesting post. It's news to me but i doubt this explanation (even if it's true), as I had no knock for 37,000 miles and then it suddenly appeared.
I'm convinced it's a tolerance and/or wear issue (as my quotation couple of posts above states it clearly).
If it suddenly appeared that makes piston slap a very unlikely cause. It should have been there from new. You would have to be terribly abusive to wear out an engine in 37k miles!
I'd check that fancy valve gear.
Originally Posted By: SteveSRT8
If it suddenly appeared that makes piston slap a very unlikely cause. It should have been there from new. You would have to be terribly abusive to wear out an engine in 37k miles!
Not necessarily. As you recall from my above posts, often times solid moly resin coating is used on those short skirts to prevent knocking when new. When that soft coating wears out (usually after warranty), knock develops. That was a case in early 2000's Subarus.
I was advised by numerous people on Toyota forums not to worry about it. Being a full fledged oil nerd, I'm on a quest to see if oils/additives can cure that.
Will report back if I find something that works.
If it suddenly appeared that makes piston slap a very unlikely cause. It should have been there from new. You would have to be terribly abusive to wear out an engine in 37k miles!
Not necessarily. As you recall from my above posts, often times solid moly resin coating is used on those short skirts to prevent knocking when new. When that soft coating wears out (usually after warranty), knock develops. That was a case in early 2000's Subarus.
I was advised by numerous people on Toyota forums not to worry about it. Being a full fledged oil nerd, I'm on a quest to see if oils/additives can cure that.
Will report back if I find something that works.
Thanks, I'd be interested to see any info on this as it develops.
Geometry is an interesting part of it...
Back years ago, they used to offset the wrist pin a little to stop the piston rock at TDC, which made TDC and little off the theoretical crank position, and the "knee lock-up" point different as well.
The racer of the day found that accidentally installing the pistons "backwards" made more power, and more rattles.
Back years ago, they used to offset the wrist pin a little to stop the piston rock at TDC, which made TDC and little off the theoretical crank position, and the "knee lock-up" point different as well.
The racer of the day found that accidentally installing the pistons "backwards" made more power, and more rattles.
Indeed, the geometry is an interesting piece of the puzzle. Bore, stroke, rod length, it gets a bit complicated.
In the 'old daze' you never heard piston slap unless it was a racing motor with big clearances, forged pistons, etc. Or if it was completely worn out.
Hearing it in a brand new engine was very disconcerting the first time for me. But it has not affected the life or performance of the engine at all, even at 400k miles.
In the 'old daze' you never heard piston slap unless it was a racing motor with big clearances, forged pistons, etc. Or if it was completely worn out.
Hearing it in a brand new engine was very disconcerting the first time for me. But it has not affected the life or performance of the engine at all, even at 400k miles.
Originally Posted By: SteveSRT8
Indeed, the geometry is an interesting piece of the puzzle. Bore, stroke, rod length, it gets a bit complicated.
In the 'old daze' you never heard piston slap unless it was a racing motor with big clearances, forged pistons, etc. Or if it was completely worn out.
Hearing it in a brand new engine was very disconcerting the first time for me. But it has not affected the life or performance of the engine at all, even at 400k miles.
Depends on whose "Old Daze" you are talking about. ( : < ) My "Old Daze" had a lot of Rover V8s in them back to the '70s and well into the '90s... and piston slap was part and parcel of those powerplants. Between the spotty quality control everpresent in British manufacturing in those days, and the noise transmission qualities of aluminum blocks, piston slap was very common but, as you said, benign. I spent a fair bit of time miking pistons and bores trying to achieve that "magic clearance" point where the engine wouldn't talk back. High end customers, you know. Noise=bad! No talking them out of it. In some of the early years of the NAS Range Rovers we had a lot of trouble with piston noise on new engines. Other years, not so much. For years after I quit working on them, I had boxes of slightly used Rover 3.5 and 3.9L V8 pistons from warranty repairs. They were all just a tiny bit to small to be quiet in a standard or honed bore but perfectly serviceable in every other way.
Indeed, the geometry is an interesting piece of the puzzle. Bore, stroke, rod length, it gets a bit complicated.
In the 'old daze' you never heard piston slap unless it was a racing motor with big clearances, forged pistons, etc. Or if it was completely worn out.
Hearing it in a brand new engine was very disconcerting the first time for me. But it has not affected the life or performance of the engine at all, even at 400k miles.
Depends on whose "Old Daze" you are talking about. ( : < ) My "Old Daze" had a lot of Rover V8s in them back to the '70s and well into the '90s... and piston slap was part and parcel of those powerplants. Between the spotty quality control everpresent in British manufacturing in those days, and the noise transmission qualities of aluminum blocks, piston slap was very common but, as you said, benign. I spent a fair bit of time miking pistons and bores trying to achieve that "magic clearance" point where the engine wouldn't talk back. High end customers, you know. Noise=bad! No talking them out of it. In some of the early years of the NAS Range Rovers we had a lot of trouble with piston noise on new engines. Other years, not so much. For years after I quit working on them, I had boxes of slightly used Rover 3.5 and 3.9L V8 pistons from warranty repairs. They were all just a tiny bit to small to be quiet in a standard or honed bore but perfectly serviceable in every other way.
Originally Posted By: friendly_jacek
Being a full fledged oil nerd, I'm on a quest to see if oils/additives can cure that.
What oils have you tried? Have you used any oils with a moderate amount of molybdenum in them, or have you used any molybdenum additives? I have posted before how, in my experience, the oils with the higher levels of molybdenum tend to keep my engines quietest. The 4-cylinder motors I've owned have tended to be the loudest. Havoline DS (back in the high-moly days) really quieted my '95 Nissan KA42E. So far, Valvoline MaxLife has quieted my '08 Honda K24. Next, I will use Pennzoil Platinum 0W-20, which I believe has a rather minimal amount of moly (if any at all), so I should know pretty quickly if the moly concentration is the key factor.
Being a full fledged oil nerd, I'm on a quest to see if oils/additives can cure that.
What oils have you tried? Have you used any oils with a moderate amount of molybdenum in them, or have you used any molybdenum additives? I have posted before how, in my experience, the oils with the higher levels of molybdenum tend to keep my engines quietest. The 4-cylinder motors I've owned have tended to be the loudest. Havoline DS (back in the high-moly days) really quieted my '95 Nissan KA42E. So far, Valvoline MaxLife has quieted my '08 Honda K24. Next, I will use Pennzoil Platinum 0W-20, which I believe has a rather minimal amount of moly (if any at all), so I should know pretty quickly if the moly concentration is the key factor.
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