# what oil viscocity at 40deg C should 15/50 weight oil be?

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#### StiMan

this is for my motul 15/50. what should the viscocity be? thanks

Well Mobil 1 15w50 has a viscosity of 125cst at 40c, but of course every oil is slightly different. I would suspect Motul's 15w50 would be pretty close to this. Isn't there a website with these specs listed for them?

The vicsosity range for SAE 15-vis oil at 40dC is 51 - 61, based on my interpretation of the chart, which does not have a line for '15'. Yes there is a chart, here http://www.bobistheoilguy.com/visc.html, on this site. [ January 23, 2004, 12:44 PM: Message edited by: Jeffrey Behr ]

Only certain 0W20-30 and 5W30 (M1) have a a vis of 51-61 at 40c. 15W50 oil would be over 100 at 40c. Just my two cents. Pedro [ January 24, 2004, 10:20 AM: Message edited by: pruizgarcia ]

Mobil 1 15W-50 is 125, Halvoline LPG oil 20W-50 is 174. My Penrite 20W-60 is 239 Dave.

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Originally posted by StiMan: ...Doesnt it say viscocity is about 200 to 250 for a 50weight oil?
First, it's NOT a '50weight' oil. If one uses only one number and does not specify the temp, you're talking about the viscosity at 40dC, which is the first number in a multirange oil. Your 15W-50 is a high-viscosity-index 15W oil. Look at the table at the bottom, not the complicated graph in the middle. See that an SAE-10-vis oil has a viscosity range of 41.4 to 50.6 centistokes at 40dC. See that SAE-20-vis. oil has a viscosity range of 61.2 to 74.8. Also see that the viscosity-number ranges NEVER overlap from one SAE viscosity label to the next. That means that one oil CANNOT be labeled with more than ONE SAE-viscosity number. (IOW, an oil marketer may not CHOOSE one SAE-viscosity label number rather than another--his oil's 40dC-centistoke number is within only ONE SAE range.) Therefore SAE 15-vis.'s range MUST start higher than the top of SAE-10's 50.6 and lower than the bottom of SAE-20's 61.2. That's how I came up with my range of 51 - 61. pruizgarcia, if an oil has a centistoke viscosity at 40dC of 'over 100', it would be labeled AT LEAST an SAE 30. Look at the chart again. [ January 24, 2004, 04:51 PM: Message edited by: Jeffrey Behr ]

I've often wondered why they even list the kinematic viscosity at 40 C? What use is it to you? I would worry more about the rated kinematic viscosity @ 100 C, especially the HTHS @ 150 C, which is the "real world" for your motor at operating temp. Does the SAE J300 spec even cover "recommended" values at 40 C? I see a notation for recommended mins at kinematic of 100 C and mins for HTHS @ 150 C. I would also want some CCS and MRV values, certainly the MRV BPT, in case you have low-temp concerns. Jeffrey, as a follow-up, what did you uncover wrt using Mobil 1 15W-50 in your Cayenne? Jerry

I agree with Hejay. But I also don't care what charts say what it should be. I look at the datasheets and VOA's. I always request a vis at 40c on VOA's of oils I plan or will be using. Pedro

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Originally posted by Jeffrey Behr: Therefore SAE 15-vis.'s range MUST start higher than the top of SAE-10's 50.6 and lower than the bottom of SAE-20's 61.2. That's how I came up with my range of 51 - 61. pruizgarcia, if an oil has a centistoke viscosity at 40dC of 'over 100', it would be labeled AT LEAST an SAE 30. Look at the chart again.
SAE J300 defines SAE viscosity. Last time I read it it didn't not give any requirements for 40C The viscosity of an SAE engine oil at 40C has absolutly nothing to do with it's viscosity rating.

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Originally posted by heyjay: I've often wondered why they even list the kinematic viscosity at 40 C? What use is it to you?
I really wish they would simply publish the viscosity at -20C, 0C, and 20C, this way we could see what the viscosity of these oils are under actual temperatures many of us might see. There aren't too many places in North America that you're gonna see 40C temperatures, and even in the rare places where you do, cold starting is obviously not going to be much of a problem!

Sorry Patman I was refering to the kinematic viscosity of the oil at "operating" temp of 100 C and HTHS of 150 C. Not the ambient temp. I don't think any oil test referes to the ambient temp, though some like Esso post conservative suggestions that attempt to extrapolate oil test data to recommended minimum ambient temps. Some oil companies do provide detailed cold weather test specs. Esso Canada usually tests their oil CCS and MRV values starting at -20 C down to -40 C, and also list the MRV BPT data. As XS650 mentioned, the rating at 40 C running temp is of little use to you. Most oils will see at least 100 C temps in the motor. Perhaps the most important data is the defined HTHS (High Temp High Shear) test, which subjects the oil to very high shear forces (One million shears per second) at elevated operating temp of 150 C. It's very interesting to see how an oil behaves in this severe environment. Oils with similar ratings at 100 C suddenly have VERY different ratings at HTHS 150 C, indicating they shear quite badly. Jerry

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Originally posted by heyjay: Sorry Patman I was refering to the kinematic viscosity of the oil at "operating" temp of 100 C and HTHS of 150 C. Not the ambient temp.
Yes, I realize that, and I'm simply saying that if they tested the viscosity of the oils at those temps instead of at just 40 and 100, it would give people a better idea of how the oil performs when in service. I think the 100C viscosity is the perfect hot temperature viscosity to give us, since most cars will have their oil temp relatively close to this point. But having a good idea of the viscosity of an oil when it's at a cooler temperature than 40C would give us a better idea of how to compare them to each other. Just another data point in other words, in addition to the all important cold cranking numbers.

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Originally posted by Patman:
I really wish they would simply publish the viscosity at -20C, 0C, and 20C, this way we could see what the viscosity of these oils are under actual temperatures many of us might see. There aren't too many places in North America that you're gonna see 40C temperatures, and even in the rare places where you do, cold starting is obviously not going to be much of a problem! [/QB][/QUOTE] The existing spcs do a good job of telling us the important stuff. The xx in xxW yy tells us how the oil will behave at some cold temperature. The yy tells us how the viscosity at a nice comfortable operating temperature of 100C. The HTHS spec tells us how it will behave when being abused at 150C Any viscosities between xx temp and the yy temps are of much less value because the engine only operates there while it is warming up.

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Originally posted by Patman:
quote:
Originally posted by heyjay: Sorry Patman I was refering to the kinematic viscosity of the oil at "operating" temp of 100 C and HTHS of 150 C. Not the ambient temp.
Yes, I realize that, and I'm simply saying that if they tested the viscosity of the oils at those temps instead of at just 40 and 100, it would give people a better idea of how the oil performs when in service. I think the 100C viscosity is the perfect hot temperature viscosity to give us, since most cars will have their oil temp relatively close to this point. But having a good idea of the viscosity of an oil when it's at a cooler temperature than 40C would give us a better idea of how to compare them to each other. Just another data point in other words, in addition to the all important cold cranking numbers.

So what you're trying to find are MRV values? There is a distinct difference in test procedures for testing oils at "normal" temps (Kinematic ASTM D445) and for testing their ability to pump at very cold temps (MRV using ASTM D4684). Places like Missisauga and St. Catherines have been cold enough this winter to worry about the cold MRV values. These MRV values can be hard to find, for example Mobil appears to have stopped listing them altogether and just mention "pour point" which is a useless number. Remember that MRV has an "absolute" of 60,000 cP, at this point oil fails to slump at the oil pump inlet and flow ceases. Every motor is different and some may require much lower MRV values. My 2000 GMC Sierra with Vortec 5.3 appears to be quite sensitive to MRV, and it makes a rattle/knock in winter unless I use Mobil 1 0W-30. Based on the previous Mobil 1 0W-30 data, my motor appears to be happiest with MRV's of 18,000 cP max. Esso does publish extensive MRV test values for most of their oils. I'm impressed with their Adobe Acrobat file collection. Point your browser to: http://www.imperialoil.ca/Canada-English/Products/Lubricants/PS_L_EssoAlphaIndex.asp And scroll down to "E" for the Esso Extra and XD-3 brand products. Jerry

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There is a distinct difference in test procedures for testing oils at "normal" temps (Kinematic ASTM D445) and for testing their ability to pump at very cold temps (MRV using ASTM D4684). Places like Missisauga and St. Catherines have been cold enough this winter to worry about the cold MRV values.
Most definitely! While we don't get the extreme cold like you guys in Northern Ontario get, it has definitely been a very cold January here, this morning getting down to -23C for example, and many mornings of -20 these last few weeks. I do run 0w30 German Castrol though, plus plug in a block heater on a timer (set to come on 4.5 hours before I leave) so I'm hopeful my oil analysis results from this interval will show relatively reasonable wear. I am lucky to be able to park in underground parking at work, where the coldest it's gotten down there so far has been 40F. But even still, I like to run the 0w oils just to be safe.

Patman: You hit the nail on the head by stating "just to be safe." Hate to admit it, but there are folks around here who think a 10W-30 dino is a perfectly acceptable "all season" oil. Well, sure, maybe for Kansas City ... Jerry

Yep, for me, I know 0w30 is probably overkill for an area that never sees below -25C, but to me it's not about running an oil that is just "good enough" for those temps, but I want one which handles it with complete ease. And like I mentioned, I want my winter time used oil analysis reports to show engine wear that is comparable to what others see in warmer weather. With my habits this winter, I think it might just be possible. What I'd really like to see is someone run a 10w30 conventional oil in a climate like mine through the winter months, and not use a block heater or any other aids, and have the car parked outside even. Then do a UOA in the spring to see how bad the wear is. I bet it's startling!

Patman: HA! Those folks running 10W-30 around here don't have to worry about a UOA by Spring. The thing is knocking so bad by then it's time for a new motor. Jerry

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