I'm pretty confused at this point...

Time to change oil on my 2018 Heritage m8 114. So I popped into the Harley dealer to pick up supplies. 7 quarts of Syn3, an oil filter and 3 o-rings for the plugs. That's how I've always done the three holes. The guy at the counter looks funny at me and says "I'm not about to talk you out of anything" and hustles off to get my oil. The other guy behind the counter looks at the oil and does the funny face thing that the first guy did when he said he's not going to talk me out of anything. But this guy pipes up and says that's the wrong oil for the primary.

So the recommendation was to use the Heavy Synthetic Gear Oil 80w-140 for the transmission and primary. I pull up the owners manual to see what is recommended because I want to follow the guidance that comes from the engineers...right? In the manual it says to use Formula+ Transmission and Primary Chaincase Lubricant in the primary. And the tranny can use either the Syn3 or the Formula+. But nothing saying what weight that Formula+ oil is.

So where did I get the info to use Syn3 in all 3 holes? To be honest, I am pulling up an online owner's manual. When I get home I'll check the printed manual I have in the bike's saddle bag. I wonder if the recommendations have changed.

I read through a plethora of posts in the Oil section of this forum. Most of the meaningful data I saw was based on 2006-2010. Not that I could not find a post on the M8s...I just got lazy after 2 hours and quit looking. But before I pour this stuff in, I need expert opinions from my good friends at HD Forums on this issue. LOL

I always run heavy oil in say a differential where the gears are not running super fast. It makes sense to keep them lubed with a heavy weight. But the transmission and primary have smaller, faster moving parts. Not like a motor...but also not like a pumpkin on the back of my truck. Then there's my tractor...where hydraulic fluid is used everywhere but the motor. But I always default to what the manual says. And in this case the manual says 'pick something you like'?

 

The 80w140 is great in both
You should look at a viscosity chart, the numbers aren't what you think they are

 

I am aware that most folks do not understand viscosity. Viscosity is more about how the fluid flows at various temps. A gear oil will have larger numbers than a motor oil...but have similar properties. I get that.

But to me, gear oil is used in slow moving/ heavy pressure situations. The primary may fit that but the transmission does not in my mind.

I'm willing to try new things and learn new things. But when I get confused I feel like I need to figure out why I'm confused. Why did I think it was OK to use Syn3 in the primary when the manual clearly says otherwise? Did I follow some lackey's advice or does it say that in the printed manual I have at home? I'll find out in about an hour when I go home. But I'll be liquored up by then so maybe it'll be tomorrow morning with a hang-over. LOL

 

The synthetic is not that thick nasty stuff you might be thinking of, it really is an improvement, at least in my machine. Sure I was skeptical at first, too, but after the change, the clunk quieted going N-1, and I found neutral easier to find, which on this bike was a bitch from day one.

Try it out, you will not be disappointed.

You will also hear "don't put synthetic on a clutch" which is also BS in this situation, I am laying down 149 lb/ft out of my FM 128, and I have not had a single issue with the stock clutch disks.

 

OK...so that's good info right there. First...I did picture a honey like consistency based on the label of the bottle. Glad to hear it's not like that. Second...that clunk going to fist and finding neutral. I do have a really hard time getting it into neutral. It would be nice to see those two issues improve.

 

The 2020 Softail Service Manual says either Syn 3 or Formula+ for transmission and primary.

 

This is from my 22 owners manual

 

This is from the HD site:

Heavy Synthetic Gear Oil (description)

TESTED-CERTIFIED for use in Harley-Davidson transmission and primary chaincase applications. Exclusively engineered for Harley-Davidson Motorcycles, this Heavy Synthetic Gear Oil is intended for use in extreme temperature environments (desert heat or cold weather), frequent two-up riding and heavy load riding applications.
• Dual viscosity (SAE 80W-140) heavy weight gear & primary oil
• Developed with proprietary additives and pure synthetic base stock so it flows better at cold start-up then in high temperatures viscosity behaves like a 140 weight oil to provide maximum protection
• Formulated to maintain the proper coefficient of friction for clutch operation and provide superior lubrication for the primary chain drive
• Provides specialized lubricity for the anti-wear requirements of transmission gears across a wider temperature range than mineral based oil
• Approved by Harley-Davidson for use in all stages of transmission and primary chaincase life
• Not for use in the crankcase as a motor oil

This product was not available until a couple of years ago ( or at least, I was not aware of it). I used to use SYN 3 in all three holes. Now I use the heavy syn gear oil for the transmission and primary.

Nice to have options to argue over in forums...

 

I'm not an oil engineer, I go by feel and the seat of my pants. Not really understanding the recommendation of the 80W-140 in cold weather? Hot weather like June/July/August in Texas? Yes....

Last October for ***** and giggles before I rode to North Carolina from Texas on my Ultra Limited, I changed all 3 holes as usual, and for the ***** and giggles part I used the 80W-140 in both the transmission and the primary.

The weather was cool to chilly, and not a fan of the results. May try it when it gets hotter than hell this summer, but as soon as I got home I pulled the plugs and went back with my Redline go to.

 

I suggest you use what it says in your service manual. When Harley first came out with SYN 3, they said all three holes.

Years back, on a lot of models, the service manual said it was the second option now referring to Formula+ non detergent straight weight gear oil for the primary and transmission as first choice.

From an engineering stand point, you don't want a high detergent motor oil in a non filtered gear box. You also don't want a EP oil in a clutch box.

Now will you notice the difference? Years of trying things tells me no.