Engine noise and oil viscosity

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It seems thicker oil makes at least some engines run more quiet than a thinner oil. Now, people keep saying that just because an engine sounds better it still doesn't mean that this is better for the engine. What's the reasoning behind that claim? My gut tells me to switch viscosity if my engine is ringing. A smooth and quiet engine is a happy engine, no?
 
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The reasoning is that a thicker oil may not be lubricating any better, or even as well, it's just acting as a noise damper. My experience is that thicker oils cause higher oil temps and don't flow as well when cold. Neither is good. Others have also talked about how they don't believe they clean as well, shear issues, etc. Obviously there's an optimum weight for any given engine and conditions but I don't think you can tell by sound... [ August 13, 2003, 11:28 PM: Message edited by: jsharp ]
 

moribundman

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quote:
The reasoning is that a thicker oil may not be lubricating any better, or even as well, it's just acting as a noise damper.
The thicker oil may well be lubricating better, depending on conditions. How can a miniscule oil layer function as an effective noise damper? Where does the sound come from? From vibrations? Where do the vibrations come from?
quote:
My experience is that thicker oils cause higher oil temps and don't flow as well when cold. Neither is good. Others have also talked about how they don't believe they clean as well, shear issues, etc.
Yeah well, cold weather is not a problem for all people. An engine may well be designed for thicker oil, so oil will flow just fine with the thicker oil. Why would a thicker synthetic oil clean worse than thinner one? The engine will probably burn less of the thicker oil, resulting in less deposits.
quote:
Obviously there's an optimum weight for any given engine and conditions but I don't think you can tell by sound...
The sound-doesn't-matter-issue is what I'm questioning. We are talking about a thin versus a thick oil film here. Again, how much sound dampening can be attributed to a still miniscule layer of oil?
 
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quote:
Originally posted by moribundman:
quote:
The reasoning is that a thicker oil may not be lubricating any better, or even as well, it's just acting as a noise damper.
The thicker oil may well be lubricating better, depending on conditions. How can a miniscule oil layer function as an effective noise damper? Where does the sound come from? From vibrations? Where do the vibrations come from?
quote:
My experience is that thicker oils cause higher oil temps and don't flow as well when cold. Neither is good. Others have also talked about how they don't believe they clean as well, shear issues, etc.
Yeah well, cold weather is not a problem for all people. An engine may well be designed for thicker oil, so oil will flow just fine with the thicker oil. Why would a thicker synthetic oil clean worse than thinner one? The engine will probably burn less of the thicker oil, resulting in less deposits.
quote:
Obviously there's an optimum weight for any given engine and conditions but I don't think you can tell by sound...
The sound-doesn't-matter-issue is what I'm questioning. We are talking about a thin versus a thick oil film here. Again, how much sound dampening can be attributed to a still miniscule layer of oil?

But the ultimate thickness of the oil film under load isn't what we're talking about here. We're talking about the possible sound damping effect of a thick film of oil before it's under load or while it's being loaded and moved around. IMO, it's often acting as a vibration dampener/insulator and nothing more. From first hand experience - I built and raced a number of Kawasaki 550/650/750 and 900/1000/1100 engines in the late 70's and early 80's. These were DOHC air cooled 4 cylinder engines with bucket type flat tappets on top of the valves that the cams worked directly. We used short skirted slipper type pistons ( gasp, no oil control rings! ) in some and often very radical cams with very rapid valve accelerations. Valve clearances were on the order of .002"-.004", more with some cams. The primary drive to the transmission used straight cut gears. These engines were always noisier with lighter oils. Keep in mind when I say lighter vs. heavier here I mean 10W-40 vs. 20W-50 or straight 40 and 50 weights. I believe the majority of the sounds we were hearing were the sounds of the cams working the tappets as they actuated the valves, and also the primary drive. No real piston noise to speak of since those clearances were on the order of .002" and the piston speeds were low as were the piston rocking forces. So while they made more noise with thinner oil, they also made more power and ran lower oil temperatures. What did the thick oil do for us other than make them quieter? Nothing in that application that I could find... As far as cleaning, I won't say it's always the case that a thinner oil would clean better but I could see why it *might* Higher flow rates and lower temperatures would help keep things clean no? I think we need an acoustic engineer to answer this for sure [Wink] but it makes sense to me a thicker fluid would be a better vibration dampener than a thinner fluid. [ August 14, 2003, 01:47 AM: Message edited by: jsharp ]
 
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The damping effect of lube oil is very significant to any mechanical system. Ask any vibration specialist and they will go on and on about viscous damping and how it affects dynamic systems. A more viscous fluid has greater internal damping. This should increase the damping on the system making it quieter (less movement).
 

moribundman

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23,591
quote:
But the ultimate thickness of the oil film under load isn't what we're talking about here. We're talking about the possible sound damping effect of a thick film of oil before it's under load or while it's being loaded and moved around. IMO, it's often acting as a vibration dampener/insulator and nothing more.
Well, yeah, but, I do run my engine mostly under load... Okay, so you were talking only about valve train chatter, hydraulic lifter noise, etc? Hmm, I can't tell a difference at startup between the 5W-50 and a 0W-40, but I can hear a difference at idle when the engine is hot.
quote:
From first hand experience - I built and raced a number of Kawasaki 550/650/750 and 900/1000/1100 engines in the late 70's and early 80's. These were DOHC air cooled 4 cylinder engines with bucket type flat tappets on top of the valves that the cams worked directly. We used short skirted slipper type pistons ( gasp, no oil control rings! ) in some and often very radical cams with very rapid valve accelerations. Valve clearances were on the order of .002"-.004", more with some cams. The primary drive to the transmission used straight cut gears. These engines were always noisier with lighter oils. Keep in mind when I say lighter vs. heavier here I mean 10W-40 vs. 20W-50 or straight 40 and 50 weights. I believe the majority of the sounds we were hearing were the sounds of the cams working the tappets as they actuated the valves, and also the primary drive. No real piston noise to speak of since those clearances were on the order of .002" and the piston speeds were low as were the piston rocking forces.
Cam noise and valve train noise make sense, but I still don't see how a thin layer of oil can make an audible difference, unless there is more going on that just sound dampening.
quote:
So while they made more noise with thinner oil, they also made more power and ran lower oil temperatures. What did the thick oil do for us other than make them quieter? Nothing in that application that I could find...
I'm not sure why you would see lower oil temps at startup as a plus. You'd want the oil to get hot fast, right? Or are you not talking about startup anymore? [Wink]
quote:
As far as cleaning, I won't say it's always the case that a thinner oil would clean better but I could see why it *might* Higher flow rates and lower temperatures would help keep things clean no?
How much differnce in flow rate are we talking about? I would suspect that the type of oil has a bigger effect on engine cleanliness than the oil flow rate.
quote:
I think we need an acoustic engineer to answer this for sure [Wink] but it makes sense to me a thicker fluid would be a better vibration dampener than a thinner fluid.
I don't know, better vibration dampening sounds good to me. Vibration can't be good, or is it really negligible? By the way, I'm not trying to be a jerk here, even if I come across as one. I'm just trying to find out more. [Wink]
 

moribundman

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23,591
quote:
The damping effect of lube oil is very significant to any mechanical system. Ask any vibration specialist and they will go on and on about viscous damping and how it affects dynamic systems. A more viscous fluid has greater internal damping. This should increase the damping on the system making it quieter (less movement).
sub_zero, And do we know if there is ANY correlation between dampening and wear and tear, or is undampened noise (for lack of a better term) completely harmless? As you just pointed out, this is a significant issue regarding mechanical systems. All vibration specialists, step forward, please! [Cool] [ August 14, 2003, 02:22 AM: Message edited by: moribundman ]
 
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My gut feeling is that noise (tapping/knocking type noise) is due to pieces moving at reasonable velocities, and running into other pieces. In general engineering terms that's always bad news, as the impact loads are many times more stressful than gently applied loads. However, if the stresses applied in this manner aren't enough to induce fatigue failure, the parts don't fail. Wear on cam ramps might be higher, and bearings a little less well off than they would be. On basic engineering, I dislike noise. When I tried M1 0W-40 in the 4Runner (from 5W-50), it sounded like a steel bucket full of ball bearings. I didn't like it, and went to Delvac 1, which "sounds" like the 5W-50 did WRT the racket. 50-50 Delvac 1 and 0W-40 still sounds good. The camira went from 15W-40 to 25W-70, with no noticeable change in engine noise, i.e. from bugger all to bugger all (scientifically validated). 'bout Christmas time, it will get an xW-30, and I'll see how noisy (or not) it gets.
 
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I don't really know if more damping will decrease or accelerate wear. I would think you need the right amount of damping to keep parts separated and the vibration controlled. Tooo much damping could lead to excess heat. I know the damping properties of oil are usd in what are called 'squeeze film bearings' were a film of oil is used between the bearing housing and the bearing OD, usually a clearance of a few thou. This will significantly decreases the measured vibration of the machine. Since vibration can occur in the audible range, depending on machine speed the squeeze fiml damping should quiet the assembly.
 
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quote:
Originally posted by moribundman:
quote:
But the ultimate thickness of the oil film under load isn't what we're talking about here. We're talking about the possible sound damping effect of a thick film of oil before it's under load or while it's being loaded and moved around. IMO, it's often acting as a vibration dampener/insulator and nothing more.
Well, yeah, but, I do run my engine mostly under load... Okay, so you were talking only about valve train chatter, hydraulic lifter noise, etc? Hmm, I can't tell a difference at startup between the 5W-50 and a 0W-40, but I can hear a difference at idle when the engine is hot.
quote:
From first hand experience - I built and raced a number of Kawasaki 550/650/750 and 900/1000/1100 engines in the late 70's and early 80's. These were DOHC air cooled 4 cylinder engines with bucket type flat tappets on top of the valves that the cams worked directly. We used short skirted slipper type pistons ( gasp, no oil control rings! ) in some and often very radical cams with very rapid valve accelerations. Valve clearances were on the order of .002"-.004", more with some cams. The primary drive to the transmission used straight cut gears. These engines were always noisier with lighter oils. Keep in mind when I say lighter vs. heavier here I mean 10W-40 vs. 20W-50 or straight 40 and 50 weights. I believe the majority of the sounds we were hearing were the sounds of the cams working the tappets as they actuated the valves, and also the primary drive. No real piston noise to speak of since those clearances were on the order of .002" and the piston speeds were low as were the piston rocking forces.
Cam noise and valve train noise make sense, but I still don't see how a thin layer of oil can make an audible difference, unless there is more going on that just sound dampening.
quote:
So while they made more noise with thinner oil, they also made more power and ran lower oil temperatures. What did the thick oil do for us other than make them quieter? Nothing in that application that I could find...
I'm not sure why you would see lower oil temps at startup as a plus. You'd want the oil to get hot fast, right? Or are you not talking about startup anymore? [Wink]
quote:
As far as cleaning, I won't say it's always the case that a thinner oil would clean better but I could see why it *might* Higher flow rates and lower temperatures would help keep things clean no?
How much differnce in flow rate are we talking about? I would suspect that the type of oil has a bigger effect on engine cleanliness than the oil flow rate.
quote:
I think we need an acoustic engineer to answer this for sure [Wink] but it makes sense to me a thicker fluid would be a better vibration dampener than a thinner fluid.
I don't know, better vibration dampening sounds good to me. Vibration can't be good, or is it really negligible? By the way, I'm not trying to be a jerk here, even if I come across as one. I'm just trying to find out more. [Wink]

When I was talking about "load", I meant the actual loads on the internal parts, not the engine "load." Few of the parts in a reciprocating engine with cam driven valves are under a constant "load." In the case of a solid tappet for example, it varies from "no load" when the valve is closed and there is valve clearance, to "maximum load" somewhere during the valves actuation. Hydraulic lifters are another animal altogether. Aren't they supposed to be silent? [Smile] I don't know how you inferred I was talking about just startup noise or oil temps, but I wasn't. I'll agree the type of oil matters more in engine cleanliness than weight. But we're talking about weight as the only difference here. Vibration dampening is a good thing I suppose if you can get it for free. But it has about as much value as it costs IMO. I sure wouldn't trade higher oil temps and lower flow rates and the potential problems they might cause just to make things quieter. Everything else being equal, as long as the film strength of an oil is sufficient to keep the parts separated under the loads involved, I just can't see any real advantage, and see a number of disadvantages to using heavier oil...
 

moribundman

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23,591
quote:
I don't know how you inferred I was talking about just startup noise or oil temps, but I wasn't.
I thought so because you had said the following earlier: "But the ultimate thickness of the oil film under load isn't what we're talking about here. We're talking about the possible sound damping effect of a thick film of oil before it's under load or while it's being loaded and moved around."
quote:
Vibration dampening is a good thing I suppose if you can get it for free. But it has about as much value as it costs IMO. I sure wouldn't trade higher oil temps and lower flow rates and the potential problems they might cause just to make things quieter.
Well, if my car calls for a 5W-40, then I guess it makes sense not to use a 0W-40 if that makes it sound worse. As for the best viscosity, yes I agree, the oil should be as thin as possible, but also as thick as necessary. Also, I've never run into problems with oil that was too thick in this climate, but I have had problems with oil that was too thin.
 
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I do a lot of WOT on my 2000 camry 2.2L, here is my opinion: Shell Helix Ultra 15w50: Noticeably quieter with WOT. But more valve tick during idling (only if you open the hood and listen real closely). Very low wear. Shell Helix Ultra 5w40: Noticeably louder with WOT, but less valve tick during idle. Wear doubles.
 
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It seems to me if the oil is thick enough to keep the metal parts apart there won't be the banging noise. I doubt there is much dampening of the noise with the sharp loud noise we are talking about on start up I think what is being dampen is the parts coming together.
 
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I've got a '94 Mitsubishi pickup 67k miles.. It owes me nothing, been extremly reliable BUT it does have 2 minor issues. 1- uses a qt. per 1000 miles .... 2- has a sometimes lifter tick that lasts for 5 minutes right after start up.... If I run 10-40 the oil consumption gains a little & the lifter tick gets worse. Engine likes 10-30 or 5-30, but with the 5-30 it drinks a little more oil bringing consumption to 1 qt. every 900 or so.. {BTW I have Auto-RX on order cant wait to see it it improves these issues...} those are my experiences with engine noise & oil viscosity [Patriot]
 
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