quote: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?
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.
quote: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.
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.
quote: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?
Obviously there's an optimum weight for any given engine and conditions but I don't think you can tell by sound...
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. 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
Originally posted by moribundman:quote: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?
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.quote: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.
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.quote: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?
Obviously there's an optimum weight for any given engine and conditions but I don't think you can tell by sound...
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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 ]quote: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.
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.
quote: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.
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.
quote: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?
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...
quote: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.
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?
quote: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.
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.
quote: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!
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).
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[ August 14, 2003, 02:22 AM: Message edited by: moribundman ]quote: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?
Originally posted by moribundman:quote: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.
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.quote: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.
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.quote: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?
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...quote: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.
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?quote: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.
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.
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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...quote: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."
I don't know how you inferred I was talking about just startup noise or oil temps, but I wasn't.
quote: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.
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.
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