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Choosing the correct Oil for a wet-clutch Motorcycle

Discussion in 'XJ Technical Chat' started by k-moe, Jul 27, 2013.

  1. anachronism

    anachronism Member

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    It does not "magically" become a higher viscosity oil.

    All oils (used in combustion engines, I don't want this to get esoteric) thin as they warm. A 5 weight oil at 20* may be more viscous than a 50 weight oil at 150*.

    Historically, oils were sold in a single viscosity grade. A common one that still exists is SAE 30W oil. A single oil will thin as it heats in a more or less linear fashion.

    Multi weight oils thin less as they heat, due to either the addition of Viscosity Index Improvers, or due to the properties of the base (synthetic oils). Compared to single grade oils, as multi grade oils heat up, they don't think as quickly as single grade oils. Thus in the case of 5W-30, a 5 weight oil when at the tested temp (which I believe is somewhere in the operating range) will be expected to have a similar viscosity (thickness) as a single grade 30 weight oil. As the multi grade oil heated, it didn't thin out as fast.

    So.. great, we should all run 0-150 W oils for the best of all worlds!

    No.

    Two problems:

    1. Viscosity Index Improvers aren't great. For one, they aren't great lubricators, but the bigger problem is that they break down much faster than the rest of the oil. They are made up of long chains of polymers that shear apart, after which they don't work to slow down thinning. They also tend to break down into sludge. This means that a 5W 50 oil may work exactly like that fresh out of an oil change, but after life in an air-cooled engine getting munched through transmission gears, it can turn into a sludgy thin 5W oil before that next oil change. Using oils with a larger range 10W-40 vs 10-W30 generally means a shorter oil change interval is warranted because more VII's were used to keep the oil thicker once heated. Synthetics tend to start with more favorable properties (they thin less when heated before the addition of VII's), which is one big reason they can withstand longer oil change intervals.

    2. It is pretty easy to have too thin an oil. Metal expands when it warms, so a cold engine has more clearance- a few thousands extra all across the board. When cold, a too thick oil will be slow to get pushed through the lubrication system, leading to wear from insufficient oil on startup. But a too thin oil may not be able to coat and provide a sufficient film for engine parts to glide on instead of pushing through to metal bearings. Engines are designed with a specific oil spec, and generally engines with looser clearances spec thicker oils. One reason some auto engines now spec 0 weight oils is because better manufacturing has allowed them to tighten bearing clearances (and lighter oils help fuel economy). A small block Chevy from the 60's doesn't have bearings that tight, and needs some syrup to the oil to avoid wear.

    Important to note that the first number in a multi grade oil is NOT just the startup thickness- That is the base viscosity of the oil. The oil never gets thicker than that- it just doesn't thin as much as one would expect if it was a single grade oil. If an engine was built expecting a 20W oil, and a 5 weight oil is put in instead, the engine may see adverse effects in the performance window where the 5W oil is thinner.

    Also notable that all oils of a given grade still don't act the same. I've observed in cold temps that many synthetics will pour easier than non-synthetics. That same difference I observe when pouring the engine will observe when starting, for better or worse. I fully expect that at whatever temp the "W" portion of the viscosity is measured both synthetic and non-synthetic will be within spec, but that doesn't make them the same through the temp range. Multi-grade oils measure viscosity at two temps- oils can meet that spec while performing differently at other temps.

    http://www.machinerylubrication.com/Read/1327/viscosity-index-improvers
     
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  2. kerriskandiesinc

    kerriskandiesinc Active Member

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    The 'magically' was tongue in cheek, lol, thats why I put it in parenthesis, or whatever those commas are !! ;)

    I know it doesn't magically do anything, BUT, 5W-40.....until 0W-50 becomes available will STILL give your, or my engine THE broadest range of protection available....perhaps unless you actually DO live in Saudi Arabia, Sub Saharan Africa!! ;)

    and yes, you still need something that has better than average 'shear' strength, regardless of it's viscosity range, especially in our nightmare gearbox oil chewing factories, as motorbike gearboxes tend to be!!
     
  3. MattiThundrrr

    MattiThundrrr Not a guru

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    Quotation marks?
     
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  4. kerriskandiesinc

    kerriskandiesinc Active Member

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    Thought they had to be 'double'?? ;)
     
  5. MattiThundrrr

    MattiThundrrr Not a guru

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    If you use single quotations marks, then you should use double quotation marks for a quote within a quote. If you use double quotation marks, then you should use single quotation marks for a quote within a quote. For example: "When I say 'immediately,' I mean some time before August," said the manager.

    MattiThundrrr: putting the "punk" in punctuation!
     
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  6. anachronism

    anachronism Member

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    No 5w 40 does not give your engine "the broadest protection possible" for the reasons mentioned above. Putting a 0 or 5W oil into an engine speced for 20W is not a good idea. A 0w oil is much thinner than a 20W base oil, and that matters. It also matters how they get a 0W oil to act like a 40 viscosity oil at temp.
     
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  7. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Um....no. Recall that oils have changed along with engine materials and enginering practices. Tolerances between parts are tighter now. Our engines do not have surface treatments on the cylinder walls, or on the pistons, or modern alloys. Running lower than the recommended viscocity will increase engine wear, and eventually cause you (or the next owner) to have a very bad day.

    It's also worth noting that the lower viscocity oils are meant to provide improved oil flow during cold weather. Unless you're out riding in sub 20ºF temperatures, that 5 weight base oil is providing no benefit whatsoever.
     
    Last edited: May 20, 2017
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  8. kerriskandiesinc

    kerriskandiesinc Active Member

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    "It's also worth noting that the lower viscocity oils are meant to provide improved oil flow during cold weather. Unless you're out riding in sub 20ºF temperatures, that 5 weight base oil is providing no benefit whatsoever."

    We'll have to agree to disagree, on that one ;)

    I'm still getting the BEST 'flow'/protrction for my cold starts....regardless of the actual outside temperature....remember, once she starts to warm, my 5W.....'magically' lol, becomes 40W...But, I DO understand what you are saying, and certainly, back in the 70's/80's i could only really find 20W-50!
     
  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Empirical evidence and I are close friends. Believe the marketing department if you want, but your engine isn't going to like what they say.
     
  10. kerriskandiesinc

    kerriskandiesinc Active Member

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    I understand what you are saying, and I DO appreciate your input, and advice......

    5W..not THAT much 'thinner'...incorrect term, I know, than 10W, which was readily available, late 80's......and some of my previous XJ's ran it.....and other grades, quite successfully for over 140K miles, so I'm sticking to my guns on 'cold start protection' is just about THE most important job, one can ask of an oil! ;)

    I will ask this though.....why do the American spec (Canadian?) XJ's not come with an oil cooler as standard?

    Most of the Euro, certainly British models do......and I can empirically and categorically state, the States is generally a LOT warmer, than the UK ;) ....I'd have thought an oil cooler was a MUST have, over here?
     
  11. anachronism

    anachronism Member

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    They didn't specify 20w 50 vs. thinner weights because "better" oil was not available, they did it because it is an air-cooled engine subjected to high temps and needs thicker oil.

    The CB750 nighthawk was one of the last UJM's made, well into the 1990s with air cooling. It specs the same 20w 50 for Summer use.
     
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  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    My opinion is that the U.S. market did not get oil coolers for a few reasons. Firstly, Yamaha U.S.A. was known for trying to eek-out every bit of profit they could, so U.S. machines often got different equipment (e.g. the crappy first-generation Virago starter that nobody else had to deal with). The other reason is the 55 mph national speed limit of the time. The XJ engine is well cooled without an oil cooler when riding under those conditions, so Yamaha U.S.A probably didn't think it was necessary to fit an oil cooler.
     
  13. MattiThundrrr

    MattiThundrrr Not a guru

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    And yamaha was in no way being naive in assuming that no American would exceed the posted limit!
     
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  14. Stumplifter

    Stumplifter Well-Known Member

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    :D:D:D


    Matti - glad you are still poking your head in here once in awhile.

    I often times misuse 'the single' as a way of "quoting" someone but not necessarily verbatim.
     
  15. MattiThundrrr

    MattiThundrrr Not a guru

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    THAT'S WHAT SHE SAID!
     
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  16. Edgar Olivo

    Edgar Olivo Member

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    Will the Rotella T4 15w40 work for me in the Texas heat or will I have to go with the 20w50 for more heat?
     
  17. twinky

    twinky Member

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    i use the cheapest walmat oil i can buy. i've got 55,000 miles on a superglide doing that. the trans is fine. chaincase too....
     
  18. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    You'll be fine. I'm only two hours north of the panhandle.
     
  19. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Juat be sure that it's JASO MA rated if you put it in your XJ. The starter clutch will thank you.
     
  20. johno

    johno Member

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    Good morning, all.

    New to the forum and have been marinating in all these oil posts

    Thank you for all the knowkedge and experience you share on this forum!

    For the original guys, long time contributors and riders - what do you use and find works best for your final drive oil?

    Thanks a bunch!

    BTW my ride: 1982 XJ650 MAXIM
     

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