[axman88]

I bought a jug of Shell T5 Rotella diesel oil last year and ran it in my C5 over the winter.  I was quite satisfied, but it didn't have enough viscosity for summer running, and my valve train was noticeably noisier with a hot engine.  The Rotella product line is 40 weight or less, and the Royal Enfield manual calls for a 15w 50 weight oil.

I found the Mystik line of oil, which is produced by Citgo Petroleum, and I intend to try some in my C5 when I change the oil in a few weeks.  It's intended as a diesel oil, and does not have JASO rating, but according to an oil analysis someone had posted found online, there are no friction modifiers that might mess with my wet clutch.  Like the Rotella, it does have quite a bit of Zinc additive, which I understand is favorable for my machine's valves.  I've read that Zinc can cause problems for catalytic convertors, but, since my machine doesn't have one of these, this caveat doesn't concern me.

https://www.mystiklubes.com/do/product/663004002
The 2 gallon jug of Mystik JT-8 15w 50 semi-synthetic was priced at only $17.60 / gallon, which translates to a $12.50 oil change, INCLUDING a new filter.  Has anyone heard of or tried this stuff?

[gizzo]

I don't think it matters whether or not there is zinc in the oil. The Enfield has roller lifters. But it won't do any harm and the gearbox might like it. Sounds like a winner and a good price, too. Welcome to the (other) dark side (diesel oil). 

[axman88]

Here's an interesting resource I found, that compares various Heavy Duty Engine Oils, including additive content.

http://www.pqiamerica.com/March2013PCMO/HDEO%20SUMMARYrev2.html

[simasa]

I bought the addionl brand, thats amazing.
https://revitakhodro.com/brand/addinol/

[Richard230]

I bought the addionl brand, thats amazing.
https://revitakhodro.com/brand/addinol/

No doubt. Do you recommend it for cooking French fries, too?   

[AzCal Retred]

The C5 is all rolling element bearings, yes? As such, it should be relatively immune to viscosity requirements, cleanliness would likely be a larger priority. Maybe it's just the hydraulic lifters that need the thicker juice to stay quiet, not the rotating bits?

[ozpacman]

I use Penrite Diesel 15 in my Bullet. Also use it in my Harleys, Victory and just about everything else. I understand it could be difficult to source in the US though.

https://penriteoil.com.au/products/hpr-diesel-15-15w-50-semi-syn