So our GS's take SE and SF rated oil but no one manufactures that anymore.  All they had at the auto store was SM and SN rated stuff.  They say its always backwards compatible but then I came across this:

http://www.aa1car.com/library/api_motor_oil_classifications.htm

Bottom section says SM oil are no good for flat tappets. I believe our cams are flat tappets also.

How true is this? Has anyone been using the SM rated oils?

As far as I know, and I've followed this for a long time, the only thing we need to worry about for our bikes is that the oil DOES NOT have the "Energy Conserving" certification.  Any oil rated SE or later, and NOT energy conserving (which implies fancy friction modifiers that don't play nice with a wet clutch) is going to be fine in your engine.

And change your oil at the recommended intervals.

Ummm no.Read a manual on the GS and check the oil specs.API SG 10-40W and it's all I run in either Valvoline or Castro(preferred).After having a PO sell me a GS with a fresh oil change that destroyed a clutch,I only use API SG 10-40w oil.

Shell Rotella T6 Synthetic oil will work just fine for your engine and is perfect for wet clutch use. $20 for a gallon at Walmart.

i checked a bunch of different brands at the auto store yesterday and they are all SM & SN. where do you find the older oil?

I ended up grabbing a jug of rotella T 15W -40, I know its not the recommended spec but alot of people here seem to be using it and I have no idea how they would be able to obtain an older version unless they stockpiled a bunch of it.

Motorcycle specific oils should still be SG type but hardly worth their premium price I think.  Biggest difference between them and API rated oils like current SM,SN etc is the removal or reduction in the film strengthening additives like zink which were harmful to auto cat converters.   Such additives are more important in motorcycles using the engine oil to lubricate the trannys because the shearing action of the gears breaks down the oil faster.  Other major factor is the energy conserving additives that can cause a wet clutch in a bike to slip but there are 10W-40 and higher viscosity API SM oils that don't have these.  

The heavy duty oils aka truck/deisel oils like Rotella T, Delvac, Delo, etc have more of the desirable zink additive and no energy conserving additives making them desirable for bikes.  Also the the Rotella T now has the JASO MA rating meaning it meets motorcycle specs, JASO is the Japanese agency like our API that rates motor oils.  There is also a JASO MB rated oil with energy conserving additives for bikes with dry clutches so make sure you get MA.  

As far as meeting the recommended viscosity spec this should cover it:

ok cool, that helps alot. thanks!

so basically, if im going to use car oil then avoid the SM SN because of the decrease in zinc additive and energy conserving chemicals

or

go for motorcycle specific oil but this can be expensive

or

go with the heavy duty diesel oils like rotella and generally do not have additives and has plenty of the zinc additive.


am i missing anything?  if not i will go ahead with the rotella T SN oil that i purchased. cool?

The Rotella T 15W-40 conventional oil is my current choice for use year around here in NE Ohio until something better comes along.     I used 15W-50 Mobil 1 synthetic for the first 50k miles in my 97 GS and after oil consumption increased considerably with advancing milage I switched to the less costly 15W-40 Rotella/Delvac type heavy duty oils.  I've used only the heavy duty oils in my current 02 GS for over 80k miles now.

I give 3.99 (x 4=15.96) a quart of MC oil at Auto Zone.That's cheaper that a gallon at $20.I was getting a case of 12 quarts for $32 through my local NAPA,but it went out of business.

...I've been going on for months about the heavy duty "diesel" oils but no one seems to be catching on, I've been using it for years, ever since a bike mechanic told me it's the best kept secret in the business, he said it is every bit as good and even superior to 6 and 8 dollar a quart motorcycle specific oils in every way.

Quote from: ojstinson on May 13, 2011, 09:09:49 AM
...I've been going on for months about the heavy duty "diesel" oils but no one seems to be catching on, I've been using it for years, ever since a bike mechanic told me it's the best kept secret in the business, he said it is every bit as good and even superior to 6 and 8 dollar a quart motorcycle specific oils in every way.

No secret at all here my friend, many of us use that, I however went from it to the accel oil from walmart - sf rated oil that is actually just about a hair cheaper than the rotella/delo ones.
Cool.
Buddha.

Never heard of it but I think I'll check it out on my next trip to Walmart. I looked around the various oil forums and it seems to be very popular.

Thanks for the heads up.

You talking about accel - I haven't bought it in a year or so, but they should still have it. Its 10w40 and best of all its SF rated and it says on the bottle not for cars newer than 1990. Lots of phosphorus and zinc I believe, which really work to save the bearings.
Cool.
Buddha.