Mobil 1 15W50 or Mobil 1 V-Twin 20W50 in my R100 Airhead?

I'm thinking I want to use Mobil 1 in my 1979 R100RT engine but not sure if I should use Mobil 1 15W50 (auto) or Mobil 1 V-Twin 20W50 (motorcycle)?

There's a lot of chatter over on the oilhead side, but search comes up with nothing on the airhead side about either Mobil 1 oils.

So, any airhead owners using Mobil 1?

If so, are you using Mobil 1 15W50 designed for cars or Mobil 1 V-Twin 20W50 designed for motorcycles?

I know the Mobil 1 V-Twin 20W50 has stuff in it for engines that have common crankcases for engine/trans/wet clutch, like my Honda's and Suzuki's have, but the airhead engine does not share it's crankcase with the transmission and it has a dry clutch so it seems that the Mobil 1 15W50 designed for car engines would be the logical choice here.

Then there's the whole 15W50 vs 20W50 thing...

Anyone? Anyone? Bueller?

TINK

I'll dive in.......

You want an oil suitable for flat tappet OHV engines not fitted with catalytic converters.

Such oils come with plenty of ZDDP an additive used until quite recently in oils but taken out because it does not work well for catalytic converters.

I use a Valvoline VR1 20-50 oil marketed towards use in classic racing cars and bikes. It contains ZDDP. It's a mineral oil. API SL

Oils available in your country will vary and castrol 20-50 sold in Europe is probably formulated differently that Castrol 20-50 sold in the US.

Hello !
Your bike has a separate gearbox. So it is more like a car than another bike. (there are some cars with the gearbox in the same box as the engine but they are the minority).
But, I for one, disagree with synthetic oil in an airhead (and in an oilhead too). These oils have trouble conforming to the maximal viscosity (the 50 figure). So they often fail when we need them : when it's hot and we ride hard... (you can check this by comparing the viscosity of hot 15W50 synthetic and 20W50 mineral oil. The latter being more viscous than the former... )
Last but not least, BMW warn against using API SJ and above oils in an airhead because these oils lack a lot of additives which are very useful in an airhead designed a long time ago with the metal of the era. Metals used in today's cars are very different.... so oil needs are very different too.
I would stick to a car oil from mineral base 20W50 viscosity rated API SF~SG or SH as BMW advised to use... And this will save a lot of money too...

There is insignificant difference between Mobil 1 15w-50 and Mobil 1 20w50 currently available as shown by published graphs. i have been using Mobil 1 15w50 in seven of my air cooled motorcycles since it was available. I recently switched my 83 R100 over to it after a top end overhaul. This oil is a great choice and will do well in your BMW .Change your oil and filter at the prescribed intervals and ride knowing your motor is protected.

+20 on this!!!!!! From what I've experienced with Cast 20w50 auto oil in one old car, trashed cam and tappets, I will always use oil with ZDDP in old cars or the airhead!!! The ZR1 gets high marks, synthetic is not needed especially when changing oil every 3,000 miles. Yeah I know you can extend the oil change interval with synthetics, but I have problems getting past that...5-7,000 mile oil changes I just can't bring my self to do that!!!

But it's your bike and money do what you want....

I'm a believer in the ZDDP additive for my Airhead. I have seen pictures of other rider's bikes that have pitted cam lifters and cam shafts. This is usually where the problem starts and a common factor when this is reported is the oil that was used. The most well intentioned think they are doing the right thing by using a motorcycle oil or using Synthetic oil. I stay away from motorcycle oil and Synthetics and I use an oil that I know has ZDDP in it.

I'd like to know how much ZDDP is in the oil that Chas BMW uses. He's on top of stuff but I don't know where to get these figures. How does it compare to BMW Brand motor oil? BTW that's what I use because I'm sure it has enough ZDDP in it. Of course BMW has different oils for their different vintage bikes. They have one specifically for Airheads. And it's Dino Oil. It's 20W50. I really like something a little cheaper though.

Is this the first oil thread of this winter season? Took a while didn't it?

But I don't have a dog in this fight, since I just use BMW 20w50, but I thought the ratings for motorcycles were API/SAE SJ and JASO MA. I'll verify what's on the BMW bottle when I get home tonight.

*EDIT* well, whaddya know, it's SG

I love Mobil 1 and have not run anything else in any of my motorcycles (or vehicles for that matter). But I've read enough now about airheads and the reasoning to go with "older" dino oils with higher ZDDP contents that I have been swayed.

I found this interesting response from Pennzoil while searching info on oils. It gives PPM (part per million) ratings on various API oil ratings (SH, SJ, SL, etc).

http://xs650temp.proboards.com/index.cgi?board=EngineStock&action=display&thread=14648

Well if you want the best of both worlds try 1 guart of Valvoline VR1 20-50 1900 or so ppm Zddp and 1 quart Rotella T 15/40 maybe 1300 ppm zddp mixed......ah wtf......xsjohn

Now for something completely different...

What about Castrol 4T, anyone using this? It's an old school mineral base SG oil.

TINK

Best part about this thread is that Tink is finally getting his bike finished. Can't wait to see it at the next OC vintage meet.

True, I'm moments away from firing her up. Still have the two brake masters to finish up and some other odds and ends, but I figure she should come back to life before the end of the month! I've event taken care of the insurance and will drop by AAA this week to bail her out of non-op status with fresh CA DMV regisration.

That's what I use. Meets BMW specs and is available everywhere.

In the winter I use Rotella 15w40 - 20/50 otherwise. Once I rebuld this engine I may go to synthetic, however conventional has done just fine. My 2 pennies.

I have used Mobil 1 15w-50 and the Mobil 1 motorcycle 20w-50 which Mobils markets as V twin, for Harleys. I found that the 20w-50 is quieter than the 15w-50. Some airhead gurus on the airlist do not like the car 15w-50 Mobil1.

Form the Mobil website:

"Mobil 1 V-Twin 20W-50 motorcycle oil will help provide excellent performance in motorcycle engines that are designed with a common engine/transmission lubrication system or where the engine lubrication system is separate from the transmission system. In the case of the latter, follow the manufacturer's recommendation for the type of fluid to be used in the transmission. It is also designed to help provide the proper frictional characteristics necessary for wet-clutch engine/transmission systems."

It's really quite simple. API spec SG, 20w-50. It's an air cooled engine, with it's much larger clearances at piston/cylinder compared to liquid cooled engines so 20w is better than 15w. ZDDP is exceedingly important, so some research may be needed for this as even some 'bike' oils are now using reduced ZDDP additive.
As much as I'm a strong proponent of FULL synthetic oils, I think that extending oil changes because it's synthetic is misguided. Synthetics don't break down near as fast as non-synthetics, but, they get contaminated just as fast with acidic byproducts of combustion sneaking past the bigger clearances of an air cooled piston rings. Changing the oil more often using less expensive non-synthetic oil is by far a better way to go.
If only there was available a 20w-50 diesel spec oil [api spec CC -CD], which has very high ZDDP, but most all are 15w-40, too thin for an airhead on a hot summer day.
BTW, I use Castrol 20w-50 bike oil, api spec SG.

Go to your BMW dealer and buy BMW oil. When Castrol lowered their zinc content like all the other oils I switched to the BMW 20/50. I have put over 100k on an R100 motor and every bike I build I use BMW oil without any problems. The one exception is breaking in a new motor and that is another topic.

From Mobil's website.
The 15-50 is recommended for flat tappets, but the V-Twin 20-50 has even more ZDDP.


http://www.mobiloil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf

Thank you all for playing our game today.

I decided to go with the old school oil for the old school bike, mineral base Castrol 4T 20W50 SG. Picked up three quarts at Autozone for just under $20 (5.99 each + tax)



TINK

As the airhead forum moderator on the BMWMOA forum has a call out for new oil analysis info, it's obviously not easy info to come by? How/where are you guys getting the ZDDP content for the various oils mentioned here. It seems like a no brainer to use the cheapest dino oil in the correct weight & also containing adequate zinc. So, where do you go for these figures mentioned?
FWIW, in my oilhead I use Syn Rotella T-6.