Rotella T 15w40

“For heavy-duty transmission applications, ROTELLA T Multigrade SAE 15W-40 with Advanced Soot
Control meets the requirements of the Allison C-4 transmission oil specification. The manufacturers’
recommendations should be consulted for specific types and equipment models and for appropriate
temperature range applications.”

I’ve heard of people just using whatever oil they use in there engine in there primary. When I was at Harley saying I was going to change all my oil (2008 Nightster) the guy handed me four quarts of Harley’s goop. I’m assuming he gave me four quarts so I use three in the engine and one in the primary.

Long story short, I recently have switched to Rotella T 15w40 for engine and read the above quote from Shell. Is this ok to use in the transmission?

 

My FZ1 uses the same oil for engine and trans. I run the Rotella T6 synthetic in it. I'm not sure about a Harley though. I run Redline oil and Redline primary fluid in my Sportster.

 

Have you read your Owners Manual regarding recommended engine & primary oil viscosity?
A 15w-40 is a bit light unless your in real cold weather, and is not recommended in the warmer months.
A 15w-50 or 20w-50 meets the manufacture's recommendations, especially when the weather happens to warm up for a few days during the colder months.

 

I run Rotella T 15W40 in my Sportster's engine as well. It's a great oil and I use it in everything I can and have had no problems with it in the Sportster, or anything for that matter. If you do some research, many Harley owners (and other motorcycle owners) use Rotella T with no issues. However If I lived in a real hot climate, I would probably run a heavier oil. But here we are lucky to see days where temps are above 80 in the summer months, and if we do it's only for a few days.

As for the primary I run Mobil 1 Synthetic 75W90 gear oil.

 

I have no problem running it in my engine, I'm curious thought about the transmission... From my understanding eventhough you would think the gear oil being 75w90 is more viscos than 15w40 engine oil, gear oil uses a different scale? And like the quote above, the Rotella T 15w40 has C-4 transmission oil spec, does that mean it would work?

 

I don't really know what the Allison C-4 spec amounts to, nor whether it is applicable to your HD tranny. I would make sure that it is recommended for use in "wet clutch" applications and does not have a high moly content, as that is bad news for wet clutches.

Yes, Motor Oil and Gear Oil are measured on 2 different scales.

 

It has no friction modifiers and plays well with wet clutch- I've used this in several sport bikes that share engine oil with transmission/clutch. I just don't know why the Harley would require gear oil for it's transmission...

 

Harley doesn't "require" Gear Oil in the tranny, they recommend it.
Motor Oil contains an additive package designed to deal with the by-products of the combustion process in the motor, it's of no use in the primary/tranny. Gear Oil contains an additive package designed to deal with "shearing", which occurs in gear boxes.

Most people prefer to use products that are designed to best fit a specific application, but if your goal is to make do with a "one size fits all" oil, fell free.

 

The allison C4 is uses ATF type fluids because it is a diesel automatic transmission. Yes Rotella is listed as an approved fluid and would need to be probably no higher than a 40 wt. Rotella is very good oil, but as stated I would run a 40 wt based on the owners manual outside temp range. In hotter climates I would stick with a 50 wt. The rotella T6 is an outstanding synthetic, but is hard to get just like mobile Delvac because they are for use in over the road tractors. Use it as long as you understand the viscosity rating and most if not all diesel oils are compatible with wet clutches. There are a lot of great oils out there and all will work just fine. Too much voodoo and myth on the internet about lubricants.

 

Thanks for all the good info, much appreciated.