Greetings,
Due to traffic, I am posting this here for the experts. I recently picked up an 08 SG at a great price. It only had 780 miles on it. I just changed out all the fluids at 1000 miles. I put redline in the tranny. Mobil 1 15W-50 in the engine and primary. Is the 15W-50 going to be ok in the primary? I read something about moly in this oil and didn't know if it will cause any problems. Thanks
-sunnenman

 

I run that in the primary or 20w-50 v twin and I have had no problem with either one. You should be fine. Of course with oil everyone has their own opinion.

 

I use the Mobil-1 syn automatic transmission fluid. There are friction reducers in oil which you don't want in your clutch. 15-50 does have as many as the light viscosities but you don't need any in a wet clutch. Some say it doesn't matter, maybe it doesn't but I have not had a single clutch burp, smooth a silk and neutrel is now a perfect click in every time since I started using it.

 

My last change the Indy told me to run 10w40 amsoil in the primary and of course 20w50 in the engine and the amsoil gear lube in the tranny. Ive recently switched to mobil 1 v twin oil in the engine but next time im gonna do the 15w50 in the engine and then decide what to run in the primary..

 

You can get some clutch slippage if you're using an oil with friction modifiers in it. The oils made for gassers will tend to have this in them. Most diesel oils and motocycle oils don't. The diesel oil won't say this on the bottle, but the motorcycle oils will.

 

Running a synthetic in the primary is a waste of money. The oil used in the primary is more for cooling than lubrication. A good 10w40 is more than adequate. I use Castrol GTX.

 

Thats what I've used for many miles. Buy the 5 qt bottle at Walmart, 4 for the eng and the other primary. Its overkill but handy.

 

I personally don't think we need high-tech oil in the primary, and I use a common fossil 20w50 which works very well. All you need is something to cool the cluch disks and lube the chain, which doesn't take much. A friend who's an engine builder uses ATF Type F with success.

The use of some additives like moly is good for the engine but has no place as a coolant for clutch disks. That said, I've never heard of an HD owner who's had a problem with using a high-grade synthetic in the primary, except possibly one. Someone in a recent thread here mentioned clutch slippage after swapping cams (to 255's), and he was using Amsoil 20w50. He was going to try a more mundane oil and report back but if he did I never saw his response. There was no indication that the oil was the culprit, but I have the same engine/cam setup and have no clutch slippage.

 

I run Formula+ in the primary.

 

Redline MTL works well in the primary.