Final Drive Viscosity?

[soffiler]

Bear in mind that 20 weight base stock in a 20W-50 only needs an additive package that gets it to perform like a hot 50 weight oil (2.5 times more viscous, corrected for temperature) whereas a 10W-50 needs to get 5 times "thicker" to behave like a hot 50 weight oil. IMO, if you're going to use something with such a robust additive package, you might want to consider more frequent change intervals.

SAE viscosity scale isn't linear as your post suggests, but nonetheless you're making a solid point. 20W-50 uses 20W base stock and needs less viscosity modifier to hit the SAE 50 spec when hot, versus a 10W base stock, which needs a lot more viscosity modifier to hit SAE 50 hot. Conventional oil wisdom says viscosity modifiers aren't lubricants, so the less of it, the better. I do not disagree with that philosophy.

I am checking my Rider's Manual right now ('05 GS). It calls for 20W-50 down to -10C (+14F). I personally don't ride when it's that cold, so 20W-50 works for me. Actually there's a lot of information on that page. Three straight weights, five specific multi-weights, and two more which provide some wiggle room:

SAE 10W-X Special Oils (X>=40) for temp down to -20C (-4F) and unlimited on the high end

SAE 5W-X Special Oils (X>=40) showing the widest possible range, literally unlimited on the high and low end

IF the R12S uses the same specification (I do not know the fact here) then feds27's BMW-branded 10W-50 is covered by that "Special Oils" category all the way down to four below zero fahrenheit. Brrrrr. Again, the 20W-50 is a better choice for me, all the way down to 14F.

 

[cjack]

Yes, Jack, but, is it sold in BMW-branded packaging? That's the issue I was addressing. feds27 asked "Any ideas as to who would provides BMW with 10W50 and 80W140? Valvoline, Castrol or Spectro?" and my response wondered whether ANYBODY is providing BMW with 80W/140. In other words, I think that dealer is using something else, maybe Red Line (not that there's anything inherently wrong with Red Line). I don't see any 80W/140 anywhere in the BMW system (but my info is limited to the BMW catalogs and fiche on the Max BMW site).

No. I was just guessing that the dealer has some non BMW oils for sale, so I went looking on the internet for brands of 80W140 and found Redline.
BMW has not had and does not have any 80W140 on the motorcycle side. I do not know about the car side. They generally carry Castrol there since BMWAG has a deal with Castrol...as you can plainly see from your owner's book.
BMW Motorad does have dino 10W50 motor oil though. As well as 10W40 and 20W50. The synths are 10W40, and 15W50. All made by Spectro as far as I know. For gear oils, they have 80W90 dino, 75W90 synth, and 75W140 synth. Both synths are new last year and again I think they are all made by Spectro.

 

[feds27]

I looked up the oil specs for the R12S and from what you've posted it matches the R12GS. Note that 14F is the lower LIMIT for 20W50, it doesn't necessarily mean it cold cranks or performs well at that lower limit. I don't think it's performance is linear as you suggested above. 10W40 without a doubt cold cranks much better than 20W50 at temperatures below 50F than does 20W50, and I definitely ride in that temperature range below 50F. I store my bike in a public garage that is just as cold/hot as outside temps. I have noticed a huge difference in cranking when using 10W40. There's a reason why BMW recommends different grade oils and why their range of performance overlap each other.

I would think that using 20W50 in colder weather would put more stress on the: starter, oil pump, battery, and possibly won't flow as well to lubricate all of the parts that it needs to until it warms up. Although the manual says it's safe to run 20W50 at its lower limit, why stress the bike? <= this is just my opinion. I'm not telling anyone what they should or shouldn't do. The dealer used 10W50 and that's how I became aware the grade was available. A sample to Blackstone will tell me how it performed over 3k. If it performs well then I'll keep using it.

Regarding the 75w90 and 75w140 debate. I would think that both perform similar at cold temperatures but as the FD warms up and gets to operating temperature the 75w140 gets much thicker. There is some debate as to whether thicker is better for transmissions and FDs. Some have commented on how thicker causes missed shifts in the tranny, and some have commented on how thicker doesn't allow the FD to flow oil into key areas.

 

[soffiler]

I looked up the oil specs for the R12S and from what you've posted it matches the R12GS. Note that 14F is the lower LIMIT for 20W50, it doesn't necessarily mean it cold cranks or performs well at that lower limit. I don't think it's performance is linear as you suggested above.

What did I suggest? I don't understand what you mean by that.

I would think that using 20W50 in colder weather would put more stress on the: starter, oil pump, battery, and possibly won't flow as well to lubricate all of the parts that it needs to until it warms up.

All true in theory, and the most important practical consideration in my opinion is the latter - flow when cold. In my own personal case, I tend to limit my riding to above 30F, so I've got at least a 16F "buffer window" to BMW's absolute lower limit of 14F.

Regarding the 75w90 and 75w140 debate. I would think that both perform similar at cold temperatures but as the FD warms up and gets to operating temperature the 75w140 gets much thicker.

This might be considered a nitpick but I think I detect a misconception in this statement. It doesn't get thicker, it thins to a lesser degree. The 75W spec is the "Winter" aka cold viscosity, measured at 0F. The spec without the W is the hot spec, measured at 210F. Hot 140 is substantially THINNER than cold 75 despite being numerically higher.

Interesting point implied here: how hot does an FD get? Not as hot as the transmission by a long shot, considering the tranny is connected via very good thermal paths to the hot engine, and the FD is not. Where 140 might be an improvement in the transmission, it's pretty thick for the cooler-running FD.

 

[feds27]

SAE viscosity scale isn't linear as your post suggests,

I was trying to say I agree that it's not linear, as you suggested.

 

[feds27]

I was trying to say I agree that it's not linear, as you suggested.

I read it again and that still wasn't clear. What I'm trying to say is that you suggested it's not linear and I agree. That should clear it up.

 

[soffiler]

I read it again and that still wasn't clear. What I'm trying to say is that you suggested it's not linear and I agree. That should clear it up.

Whoops, sorry for the miscommunication, and thanks for clearing that up. In short, you agree with my assertion, the SAE viscosity scale isn't linear. That's OK; I still think the point TR250Tom makes is correct, even though his illustration isn't perfect.

 

[feds27]

Interesting point implied here: how hot does an FD get? Not as hot as the transmission by a long shot, considering the tranny is connected via very good thermal paths to the hot engine, and the FD is not. Where 140 might be an improvement in the transmission, it's pretty thick for the cooler-running FD.

Yep good point. Operating temps for the tranny and FD are different. The FD definitely runs much cooler than the tranny.

I understood that 75w140 would function like a 75 weight oil at cold temperature and like 140 weight oil at operating temperature. If operating temperature is lower for a FD, does that mean 75w140 might function more like a 90 weight oil in the FD at FD operating temps? This is what I'm not entirely clear on.

 

[feds27]

Charts on Valvoline 75w90 vs. 80w140

I couldn't find charts for Spectro but I did find for Valvoline GL-5 Hypoid oil.

They show the viscosities at different temps.

http://www.valvoline.com/products/HDSYNGO.pdf



Added another chart with comparisons:

http://www.redlineoil.com/pdf/5.pdf

 

[gulfcoastbeemer]

Yes, the specified product is a European Castrol SAF-XO. NO, it is not SAE90. It is synthetic 75W/90 GL-5, as we've been discussing for, oh, 150 posts or so.

I'm glad someone is keeping track of all this. A thousand pardons...

Castrol SAF-XO is a full synthetic SAE 75W-90 final drive lubricant suitable for use in most passenger car and light commercial vehicle final drive without limited slip differentials. The excellent cold flow properties offer superior protection at start up and help to reduce torque loss and improve driveline efficiency. BMW approval for rear axles without a limited slip differential. API GL5 (GL6 obsolete), ZF TE-ML 05.

Other than having no oil at all, I rather doubt there is a single, documented case of any particular oil causing the failure of a final drive.

There hasn't been an oil manufactured that can overcome a design failure.

The absolute worst that could be said of running BMW Super Synthetic Gear Oil 75W140 verses 75W90 is BMW Super Synthetic Gear Oil 75W140 might not "reduce torque loss and improve driveline efficiency" to the same degree BMW Super Synthetic Gear Oil 75W90 might.

I smell a red herring.

 

[soffiler]

I couldn't find charts for Spectro but I did find for Valvoline GL-5 Hypoid oil.

They show the viscosities at different temps.

http://www.valvoline.com/products/HDSYNGO.pdf

Added another chart with comparisons:

http://www.redlineoil.com/pdf/5.pdf

Very interesting. Both charts have entries for 75W-90 and 80W-140. Viscosities given in centiStokes (cSt).

Valvoline at 100C: the 80W-140 is roughly twice as thick as the 75W-90 (30.6 vs 16.6).
Valvoline at 40C: the 80W-140 is more than twice as thick as the 75W-90 (284 vs 122)
Redline at 100C: the 80W-140 significantly thicker than 75W-90 (26 vs 16.4)
Redline at 40C: the 80W-140 is twice as thick as the 75W-90 (231 vs 115)

The FD does warm up; as a guess it's somewhere above 40C but not close to 100C. I think the message from Valvoline and Redline is pretty clear: the 80W-140 when warm is significantly thicker than 75W-90.

Will thicker oil cause an FD failure? I don't want to conjecture. BMW wants 75W-90 in there. Enough said.

 

[feds27]

Yep, which brings up the question that others have posted - why are dealers deviating from 75W90?

While checking for recommended final drive viscosity in my manual I double checked the oil table. Guess what I found when I flipped the page.....

Permissible viscosity classes:
SAE 5W >= 30
SAE 10W 40
SAE 15W >= 40
SAE 20W >= 40
SAE 5W >= 50

and on the back side of the page.....

SAE 10W >=50

FYI for those jumping in mid-thread my bike is a R1200S.

 

[BeemerMike]

Yep, which brings up the question that others have posted - why are dealers deviating from 75W90?

While checking for recommended final drive viscosity in my manual I double checked the oil table. Guess what I found when I flipped the page.....

Permissible viscosity classes:
SAE 5W >= 30
SAE 10W 40
SAE 15W >= 40
SAE 20W >= 40
SAE 5W >= 50

and on the back side of the page.....

SAE 10W >=50

FYI for those jumping in mid-thread my bike is a R1200S.

Uh, not sure what you are saying. The 75w-90 is gear lubricant (FD and transmission), while the "permissible viscosity classes" are engine motor oil. What is the connection between the two?

 

[soffiler]

Yep, which brings up the question that others have posted - why are dealers deviating from 75W90?

Exactly the question I've been trying to get you to ask yourself since you posted that your dealer used 80W-140!

 

[tbryant]

The "W" stands for "Winter"

The oil doesn't literally thicken, it only behaves as if it did. Have you ever seen the oil when it's hot? More like water. Following that logic, you wouldn't change the oil when it's hot...if it's thinner when cold.

 

[soffiler]

The oil doesn't literally thicken, it only behaves as if it did. Have you ever seen the oil when it's hot? More like water. Following that logic, you wouldn't change the oil when it's hot...if it's thinner when cold.

Yes. That was covered:

http://forums.bmwmoa.org/showpost.php?p=328506&postcount=156

 

[TomR1200]

Interesting discussion!

I thought perhaps I had misread the lower temp limit for 20W-50 oil based on some of the discussion above, so I just reread my owner's manual (2007 R12R). 20W-50 oil is in fact only recommended down to 32F in my bike, not 14F like the 2005 R12GS and the later R12S. I wonder what the 2007 or 2008 manual for the R12GS recommends?

Cheers, Tom

 

[TomR1200]

Conventional oil wisdom says viscosity modifiers aren't lubricants, so the less of it, the better. I do not disagree with that philosophy.

Steve, I agree with what you said, but my primary objection to "wide spectrum" multiviscosity oils is that all modifiers break down as the oil cycles and ages. You start out with 10W-50, for example, then it slowly goes out of spec. After 6000 miles, perhaps you have 10W-40? Who knows? In theory, if you ran the oil long enough to exhaust the friction modifiers, you would be running straight 10W. How long is too long for any particular grade? A wide-spectrum oil, which by definition depends more upon its additive package to deliver its advertised performance, seems more vulnerable to falling out of specification as those additives inevitably degrade.

Anyone who is still reading at this point is one of the people who cares enough about his or her oil so that they are in no danger of leaving it unchanged for 10,000 miles. But there are some good charts on RedLine's site that discuss oil falling out of spec, and that's really what I was driving at with my criticism of using 10W-50 in an air-cooled engine over 6000 mile drain intervals.

 

[feds27]

Uh, not sure what you are saying. The 75w-90 is gear lubricant (FD and transmission), while the "permissible viscosity classes" are engine motor oil. What is the connection between the two?

You jumped in mid conversation. Read a few posts back. When I posted about 80W140 I also mentioned my dealer used 10W50. I was just confirming for the skeptics that 10W50 was in my rider manual.

 

[soffiler]

... I wonder what the 2007 or 2008 manual for the R12GS recommends?

I have a good friend with an '07 GS-Adv. I have asked him to check. Will report back.