Sigh.... So many opinions so little fact.

OP. What does your owners manual, or service manual say to do? Do that. You don't have to fall for the only HD oil bullshit but do go with the weight they say.

They only way I would deviate from what they say weight wise is if someone chimed in that happened to be a research scientist in this particular field that specifically knows about this stuff. Everything else is a users opinion.

 

I was told to use a dino (Formula +) in the primary..just how slick to you want your clutch to be ?
I also use Spectro 75w140 full synthetic in the transmission and it shifts a lots smoother than even the Bel-Ray trans oil.
Mobile full syn. 20w50 in the crankcase.

 

""[quote=FBFletch;9097959]Back when Harley started running Syn 3 in all three holes, I thought it was a load of crap and I still think it's a load of crap.

First, it goes against standard practice which has been around for at least the last 50 years. Second, if it was such a great idea, every other auto and motorcycle manufacturer would have already been doing it (as Harley has never really been an innovator or leader in motorcycle technology). """"



I think the other manufactures have been doing this for years..
My 33 year old Honda use's the same oil, matter of fact it only has one hole.
that oil lubes the engine/trans/and clutch..and ....and ...and It is all mixed together
....just saying

 

Most car manufacturers have not run "gear oil" in transmissions since the 80's...in fact many manual transmission run ATF...to make them shift better. Metric bikes have run motor oil in the motor/trans since as long as I can remember. Follow the owners manual and all will be well.

 

Yes, yes & yes!

 

Thanks, i may give that a try!

 

AMSOIL 20/50 in my 05 EGC, all 3 areas. 39,000 miles and going strong. It shifts smooth, runs cooler. Never a problem.

 

dang man....havin only one hole would suck.....i like using all 3 holes...

 

2008 Twin cam with over 38,000 hard-riding miles.

This is what I have been putting in it since 1200 miles...

Motor and Primary = Amsoil 20-50

Transmission = Amsoil 75-110 Severe Gear Oil.

I would never put 20-50 in my tranny. But that's just me.

 

The only reason to run "motorcycle" oil rather than regular automotive oil is in cases where the oil is meant to lubricate a clutch. The only difference between the two is that the motorcycle oil lacks friction modifiers (primarily molybdenum) which can cause a clutch to slip, but otherwise greatly increase the protective properties of the oil.

Since a "three hole Harley" has, well, three holes, the only one which might need motorcycle oil is the primary. Putting Mobil-1 V-Twin in, say, the other two holes simply results in less protection than you'd get with a standard automotive oil, due to the lack of friction modifiers.

As far as "heavy" gear oils, well, they really aren't that heavy. 75W-90 gear oil has the same viscosity range as 10W-40 through 20W-50. You're only looking at something heavier when you go with 75W-140.

The sweet spot for lubrication is any lubricant which winds up with a viscosity of around 13-17 centistokes (cSt). For a water-cooled engine operating at about 100 °C, this would be a 0W-40. For an air-cooled engine operating in cold winter weather and not getting stuck in traffic, it would be the same (as the oil still won't get much above 100 °C). For an air-cooled engine operating in anything warmer, you'll want something more along the lines of 15W-50. I say 15W-50 rather than 20W-50 because cold starts are where most of the wear occurs, and even 15W is still too thick (35 cSt at 40 °C), with 20W being even thicker.

There are too problems with going too heavy:
1. In some designs the smaller parts with smaller cavities, such as bearings, may not receive proper lubrication and could fail prematurely. It won't grenade in 10,000 miles, but it might present itself as failing at 167,000 miles when it otherwise would have gone 180,000 miles.
2. Fuel economy/power. With a thicker oil, the engine has to use more energy to fight its own internal resistance.

I often see the explanations "well we've always done it this way" and "it's a transmission, not an engine, so it shouldn't get engine oil" used in these threads, but these come from some misunderstandings.
1. "We've always done it this way" is just another way of saying "we should ignore advances in research". Well, this isn't a good way to approach the problem of proper engine (or transmission) lubrication. Just because something has worked in the past doesn't mean it's the best available option.
2. Getting hung up on labels ignores the actual properties of the lubricant. If we are to avoid "engine oil" in the transmission because it's for engines, then doesn't that mean we should use "transmission oil" in the transmission, rather than "gear lube" which is designed for differentials?

In reality, transmission lubricants are typically in the 5W-20 range. Gear oils are the same thing as engine oils, but with some additives thrown in which are designed for the specific environment that the GL number is meant for. Most of the higher numbers, such as GL-5, GL-4, etc. are designed for a high friction environment which a Harley transmission will never see.

Harley transmissions are sequential, constant mesh, and use straight-cut and helical-cut spur gears. This is about as far from a differential as you can get. While a 75W-90 gear lube will certainly work, seeing as it's the same viscosity as a 10W-40 to 20W-50, it also contains additives which the transmission simply doesn't need, because it doesn't see the kind of conditions they're meant for.

That said, you're fine using either an automotive oil or a gear oil of the appropriate weight in the transmission. Neither one will protect to any statistically significant degree more or less than the other. Just go with a quality brand.

So what do I now run?
Primary: 10W-40 motorcycle engine oil
Transmission: 15W-50 automotive engine oil
Engine (winter): 0W-40 automotive engine oil
Engine (rest of the year): 15W-50 automotive engine oil
All of these are Mobil 1.