High Temp High Shear - does viscocity grade matter anymore ?

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(Note : excluding additive packages) There's a lot of talk on grades, low, mid, high 30, low 40 etc, and whether an engine knows the difference between a super low 40, and a super high 30. Then we all look at the HTHS number to determine how good our prospective oil is. So, is a crappy xW-40 has an HTHS viscoscity of 3.6. and super duper xW-30 has the same 3.6, does this mean that at THOSE operating conditions, the engine knows no difference ? Basically, does HTHS ultimately determine the mileage potential, and inversely affect wear ?
 
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Shannow, I use HT/HS viscosity instead of just looking at the SAE grade,which is the kinematic viscosity under a low rate of shear and really doesn't tell you how the oil is going to perform in the engine. The HT/HS is sort of a quality factor for the basestock and VI modifier .... TS
 

Shannow

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TooSlick, that's what I've gathered, and started thinking over recent months. Maybe some of our crappy old Oz dino 20W-50s were (as far as the engine is concerned) not half bad 30 or 40 weights. Dunno about our new trend of Mobil making a 20W-60 for older engines 'though
 
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It would be interesting to know if the HTHS viscosity dropped when it shears from use and then increased as it oxidized. I have a feeling that it doesn't go back up with oxidation. The reason I think this might be true is the carboxylic acid molecules clump together causing the viscosity to increase but in HTHS conditions the molecular forces might not be strong enough. Any ideas?
 
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Good question and good answer. I never really would look at this number too much until now. One of the reasons I like Amsoil and Redline is because there HT/HS numbers are very good. Redline's 5w-20 looks great for a 20wt. It looks comparable to M1 10w-30! satterfi, I think your right. If the 0w-40 thinks down a bit, it will no longer meet the 3.6 HT/HS. BTW, I tried two Ducati/Buell dealers and both didn't have Amsoil. It's just no where to be found in NJ> [ April 26, 2003, 10:26 AM: Message edited by: buster ]
 
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I'm truly appreciative of this discussion, for it is an issue that has been on my mind, regards my interest in changing my oil weight.. Thanks for the imput [ April 26, 2003, 11:07 AM: Message edited by: Luke ]
 
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Look at this study. It indicates HTHS is more important. They testeed HTHS from 1.8 to 3.0. This would include 20W oils and low end of 30W oils. SAE 980702 Properties of Engine Bearings Lubricated with Low HTHS Viscosity Oil Akira Ono, Satoru Kurimoto and Toshiaki Kawachi Daido Metal Co., Ltd. Katsuya Arai and Toshiaki Kuribayashi Tonen Corporation "The wear amount of bearings were well correlated with HTHS viscosity, not with kinematic viscosity." [ April 26, 2003, 09:03 PM: Message edited by: Fillherup ]
 
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quote:
"The wear amount of bearings were well correlated with HTHS viscosity, not with kinematic viscosity."
Very interesting and this goes along with what Steve Bergin said about Kinematic Visc. not playing a role in wear. Redline/Amsoil have it right then by using good HT/HS numbers. The Redline 5w-20 would be a great choice for a Honda Rsx or Focus SVT that calls for a 5w-20. Nice oil. I'd like to see some UOA's on this one.
 
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I have to say that I was never going to use a 5w-20 oil in my 02 Honda. However, now that I've realized the importance of HT/HS specs I am more than comfortable using the Redline 5w-20 oil. I think Redline has had it right all along with their information on their website where they actually discuss the thickness of oil at the bearing surfaces. Thick oils can actually perform less than some thinner oils due to HT/HS effects. Their 5w-20 oil is reported to have greater bearing thickness than most 5w-30 oils, due to the HT/HS considerations. To me this is a very important consideration. Perhaps we should fear good quality 5w-20 oils a lot less than we do if they have good specs. I hope to have some UOA numbers on this oil in the coming months, should be interesting. Joey [ April 26, 2003, 12:22 PM: Message edited by: Idrinkmotoroil ]
 

Shannow

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OK, but does that mean that a 5W-20 with a great HT/HS isn't as good fuel economy wise as a poorer performing one ? i.e. will a great 5W-20 out perform (wear wise) a marginal 5W-30, and will the greater HT/HS result in the lesser fuel economy from the 5W-20 than the 5W-30.
 
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Shannow, The thinner the oil, the higher the fuel efficiency, until you reach a point where you are operating under boundary or "mixed mode" lubrication conditions a significant portion of the time. When this happens wear increases dramatically and fuel efficiency drops. Clearly you don't want to get to this point! TooSlick
 

Shannow

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Tooslick, Basically what I was getting at. So there are undoubtedly some "good" 20 weights that out wear "bad" 30 weights wear wise, but provide a lesser economy than the 30 ? Would be a good marketting opportunity in a CAFE world to provide the HT/HS of a high 30, while still in a xW-20 oil (for warranty purposes and all) [Big Grin]
 
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Great discussion...great question. Although I've been pondering the same thing, we mustn't forget the whole picture. BMW is a great example. Their 5-30 is ACEA A3 rated and is therefore a better oil than OTC M-1 5-30/10-30. However, problems arose in it's use in the M cars. And I found the same thing when I used it for the past 2 years. Even though I hope the protection was there because of the A3 rating, the amount of sludge in creased due to the incorrect grade used ie. 30 was too thin. So, I now use a higher grade A3...ie a 50 weight.
 
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What I found interesting was the knee curve of the HTHS test was around 2.6. Hmmm, wonder is there is some tradeoff going on here with 5w-20 CAFE oils that just happen to be around 2.6 HTHS. Is this the tradeoff of gas milege and wear that we wonder about so much being actually shown in this paper?
 

tai

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Austin, TX
quote:
Originally posted by Fillherup: What I found interesting was the knee curve of the HTHS test was around 2.6. Hmmm, wonder is there is some tradeoff going on here with 5w-20 CAFE oils that just happen to be around 2.6 HTHS.
Does this mean anything above HTHS 2.6 is safe, and anything below is not?
 
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A factor that is rarely discussed on this board is the HT/HS viscosity of an oil after a usage interval. This would give the best indication of the shear resistance of a given oil. Satterfi brings up an important point. The kinematic viscosity increase typically seen after an extended drain interval is largely the result of accumulated polar oxidation products which can mask shearing of VI improver or the base oil itself. In theory, this effect should diminish under HT/HS conditions for the reason Satterfi described. Has anyone reported HT/HS viscosity in a UOA? It would be very interesting to know for sure if the kinematic viscosity thickening effect disappears under high temperature and pressure. The best oils would maintain HT/HS viscosity over long intervals.
 
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quote:
Does this mean anything above HTHS 2.6 is safe, and anything below is not?
What I think it means is that the tradeoff of gas mileage vs wear is at 2.6 HTHS. Anything lower and the wear is too much for the increase MPG. Higher and you get less wear, but less MPG. From a CAFE standpoint, not bad. YMMV, literally, if you really want to keep a car for a long time that may not the best tradeoff. For most folks that keep a car around 150k, they will never know the difference but slightly better gas mileage. I think CAFE is like the white collar crime of stealing a penny from each account every month. You will never notice, but he will.
 
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Is it 2.6 or 2.9 being the minimum requirement? If Mobil 1 10w-30 or 5w-30 stays in grade during the course of it's life, like in the oil study, a 3.1 HT/HS is perfectly fine then. HT/HS from what I understand is just an oils ability to withstand shearing forces. M1 10w-30 is 3.2.
 
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quote:
Originally posted by Fillherup: What I think it means is that the tradeoff of gas mileage vs wear is at 2.6 HTHS. Anything lower and the wear is too much for the increase MPG. Higher and you get less wear, but less MPG. From a CAFE standpoint, not bad. .....
Schaeffer #701 5W-30 and #703 10W-30 are both ILSAC GF-3 "Energy Conserving" and have an HT/HS vis of 3.5. Ken
 
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