Viscosity spread & VI vs shearing

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Trying to make absolutely certain I understand this correctly. Oils with large viscosity spreads (5w50, for example) require very good basestocks and/or VIIs. And in general, those VIIs will lead to shearing under extreme conditions, such as sustained WOT. This is because the VIIs breakdown under load. Conversely, oils with small viscosity spreads (5w20, for example) do not require as good of a basestock and/or fewer VIIs. Since there is less reliance on VIIs, the oil is generally more shear stable. Correct? Trying to get clarity as the weather warms here and racing season begins for my DD. Thinking a move to 10w40 might be more prudent now, and leave the 5w30/5w40 for the winter. HTHS is a very important number for racing conditions, but shearing is still a concern. The 10w40 I am considering has a slightly lower HTHS and VI than the 5w40 (4.19 vs 4.51, and 161 vs 196, respectively), but I would assume it is much more shear stable oil and better suited to racing.
 
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dparm, there are so many variables to that question, different VII's, base stock quality. Sounds like you are on to a good oil with a nice HT/HS rating and a VI that is reasonable. When I see very high VI's I start to wonder.
 
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Correct, group 5-rich basestocks. Nothing is shear-proof, and everyone here is a bit OCD, right? ;-)
 
I know I have OCD smile but I have learned allot here and that is helping me with my "doubts". I don't use motul, but the redline 5/30 I use seems to work well in my car. Dave at redline tells me the Acura TSX's that race that use redline use the 5/30 and they rev to like 10k rpm. I know our cars are turbo charged, and its true oil sheer somewhat but the poe's shear the least from what I've read. I would keep the 5/40 in. IMO. Jeff
 
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Since you're running Motul 300V, you've got a POE-based oil which is about as shear-proof as you can get. I just researched Motul specs a couple of days ago, and they are very similar to Redline in HTHS numbers for the same viscosity grades. (I would consider using them except for the $15/qt cost, lower availability, and relatively low Flash Points.) I wouldn't give up any HTHS in an oil that is used for track days. I think the Motul 300V 5w40 is good for your application.
 
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I was considering running the 10w40 for the warm months (track season) and falling back to 5w30 or 5w40 for the winter.
 
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One thing that struck me as odd when I was looking at the Motul PDS's, was they didn't list HTHS for the 10w40 300V. I took that as meaning it is about the same as the 5w40.
 
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The SAE grade "viscosity spread" as you put it is largely unrelated to an oil's VI. Some of the highest VI oils are 0W-20's with numbers over 200 and ENEOS 0W-50 is 195. Many 0W-40's aren't over 170. The XW number is it's very cold temp' performance and that's not what you're concerned with most of the time. A high VI oil basically tells you how thick the oil will be at more typical start-up temp's down to 0C or so. And even for track use a high VI as possible is desirable so that you can use high rev's as soon as possible without risking engine damage. Not surprisingly, off the shelf M1 0W-40 with it's 185 VI is commonly used as a race oil. There's no question the oil will shear some but that doesn't matter so much as it is the resulting VI of the oil in service. It's virgin HTHS vis may be 3.8cP but if it is known to shear down to 3.5cP or lower and then stabilize, that's fine if you only need a 3.3cP or 3.4cP oil. For example you could choose a lower VI HTHS 3.8cP oil such as RL which contains no VII's and it won't shear, but it will be noticeably heavier on start-up which means you can't use as many rev's cold so there is a trade off to be had. To decide what oil to use you absolutely need an oil pressure gauge. An oil that is too thick and/or has too low a VI is more of a problem than an oil that is too thin. The reason is even on a warm day, starting your track car up and heading out onto the track, even a light 0W-20 is too thick in most cars, meaning you can't use maximum rev's without the oil pump going into by-pass. It may take three or four laps to build up enough heat in the oil to enable you to do so and even then your oil pressure is well above optimum. An oil is too thin if you can't achieve normal operating oil temp's and still maintain the minimum optimum oil pressure and on the track that could mean having to pit before your track session is up. Myself, I therefore like the highest VI oil I can get with the lowest HTHS vis'(which correlates with OP) while still maintaining the minimum optimum oil pressure when the oil is as hot as it ever gets. This combination allows me to get on the gas with as few warm up laps as possible and still run even an hour or longer session. I find there's nothing more frustrating that running an overly thick or low VI oil (it's the same net out come) on the track and realize you can't safely use maximum rev's until the end of a session. Truth is, most guy have no clue about this, and windup running way heavier oil than necessary with the oil pump in by-pass mode for the entire session.
 
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Originally Posted By: A_Harman
One thing that struck me as odd when I was looking at the Motul PDS's, was they didn't list HTHS for the 10w40 300V. I took that as meaning it is about the same as the 5w40.
It's 4.19cP and it's listed here: http://www.motul-canada.com/en/products/...o_10W40_TDS.pdf But I think that must be a misprint as it's lower than the 5W-40's 4.51cP. I always thought that was way too high for a 176 VI, KV100 13.8cSt oil. I think the 161 VI 10W-40 has the 4.51cP HTHS and the 5W-40 the 4.19cP HTHS vis'; that makes a lot more sense. If someone really wants to know, send me a gallon of each and I'll be more than happy to confirm it!
 
Originally Posted By: CATERHAM
The SAE grade "viscosity spread" as you put it is largely unrelated to an oil's VI. Some of the highest VI oils are 0W-20's with numbers over 200 and ENEOS 0W-50 is 195. Many 0W-40's aren't over 170. The XW number is it's very cold temp' performance and that's not what you're concerned with most of the time. A high VI oil basically tells you how thick the oil will be at more typical start-up temp's down to 0C or so. And even for track use a high VI as possible is desirable so that you can use high rev's as soon as possible without risking engine damage. Not surprisingly, off the shelf M1 0W-40 with it's 185 VI is commonly used as a race oil. There's no question the oil will shear some but that doesn't matter so much as it is the resulting VI of the oil in service. It's virgin HTHS vis may be 3.8cP but if it is known to shear down to 3.5cP or lower and then stabilize, that's fine if you only need a 3.3cP or 3.4cP oil. For example you could choose a lower VI HTHS 3.8cP oil such as RL which contains no VII's and it won't shear, but it will be noticeably heavier on start-up which means you can't use as many rev's cold so there is a trade off to be had. To decide what oil to use you absolutely need an oil pressure gauge. An oil that is too thick and/or has too low a VI is more of a problem than an oil that is too thin. The reason is even on a warm day, starting your track car up and heading out onto the track, even a light 0W-20 is too thick in most cars, meaning you can't use maximum rev's without the oil pump going into by-pass. It may take three or four laps to build up enough heat in the oil to enable you to do so and even then your oil pressure is well above optimum. An oil is too thin if you can't achieve normal operating oil temp's and still maintain the minimum optimum oil pressure and on the track that could mean having to pit before your track session is up. Myself, I therefore like the highest VI oil I can get with the lowest HTHS vis'(which correlates with OP) while still maintaining the minimum optimum oil pressure when the oil is as hot as it ever gets. This combination allows me to get on the gas with as few warm up laps as possible and still run even an hour or longer session. I find there's nothing more frustrating that running an overly thick or low VI oil (it's the same net out come) on the track and realize you can't safely use maximum rev's until the end of a session. Truth is, most guy have no clue about this, and windup running way heavier oil than necessary with the oil pump in by-pass mode for the entire session.
Very interesting reply. Makes you wonder why all sports cars don't have oil pressure guages huh? I have looked at RL's webiste and saw that RL 0/40 has a VI of 197 and a HTHS of 4.0 Maybe this oil will suit your needs better? I too have been wanting to install an oil pressure gauge in my car, its just not so simple. Its doable, but I have to buy a few items to do it, then contimplate weather or not I would install myself or not. In a "race" setting oil pressure and oil "temps" are ideal, for DD duties maybe is overkill and that is possibly why you don't see many cars with the gauges. I must admit I have read nothing but good things about M1 0/40 and though folks say it shears a bit, with a VI of 185 and the fact it can bought anywhere and on sale at many auto parts stores often makes it an oil to consider. That Rl 0/40 looks good too though, here is the link to it. RL 0/40 Jeff
 
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IMO Red Line's 0X-XX range of oils are their best street oils; certainly their most recent formulations. RL's 0W-40 was used in the Stillen Nissan GTR in the 2009 Targa Newfoundland. Here's a UOA on the oil in a Saab: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1532313#Post1532313 Had a small amount of shear but not much considering it's unprecidently high VI. In fact I'm not aware of any 30wt or heavier oil that has a higher VI.
 
The Only Complaint that I have of the RL 0/40 though from what I see vs. other RL oils is the Evaperation Loss is much higher at 9 vs 6 of other RL oils. Additionally the Flash Point is In the 420F range where as the others are in the 480F range. To me that is a big deal when running a boosted motor that runs hot. Jeff
 
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I was hoping to find the HTHS for the motorcycle 300V 10w40, as it's probably really close to the auto (I saw this with the 5w40). Unfortunately the data doesn't seem to be published.
 
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Originally Posted By: CATERHAM
Originally Posted By: A_Harman
One thing that struck me as odd when I was looking at the Motul PDS's, was they didn't list HTHS for the 10w40 300V. I took that as meaning it is about the same as the 5w40.
It's 4.19cP and it's listed here: http://www.motul-canada.com/en/products/...o_10W40_TDS.pdf But I think that must be a misprint as it's lower than the 5W-40's 4.51cP. I always thought that was way too high for a 176 VI, KV100 13.8cSt oil. I think the 161 VI 10W-40 has the 4.51cP HTHS and the 5W-40 the 4.19cP HTHS vis'; that makes a lot more sense. If someone really wants to know, send me a gallon of each and I'll be more than happy to confirm it!
Realistically how much do you need to determine the HTHS?
 
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I'm no oil expert but if we assume the 10W40 and 5W40 have the same base oil and differing VI, lower VI for the 10W40 and higher for the 5W40, I would say that to get that high of a VI index(~200) the 5W40 must contain some VI improvers and has a lighter grade base oil. If I'm recalling the specs right the 5W40's higher volatility and lower flash point support that interpretation. I think the 10W40 would be the more grade stable and better choice for warmer temperatures and racing. I'm thinking you can't get a VI much over 170 or a grade "spread" over 20 ie (10W30)maybe 30 without VII's no matter if the base oil is ester. I know grade "spread" is kind of dubious. Both oils are probably pretty sheer resistant, but fuel dilution can also shear VII and fuel dilution is a possibility when running at power enrichment.
 
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The first 2000 on the oil didn't show much fuel dilution, even with a track day and several autocrosses. The car is not direct-inject.
 
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