I'll throw this out there, FWIW: Let's say your bike is still under warranty and you want the benefits of ATF in the primary. But you are concerned that blood red fluid in there will raise all sorts of red flags (pun intended) should you require any warranty work. A perfectly acceptable alternative would be to run a straight 20 weight motor oil. (And no, I don't mean a non-detergent oil. I'm talking about a modern API SM rated oil, but a straight 20 grade. Valvoline makes it and so do a few others.)

A straight 20 would essentially perform like Type F ATF since neither have any friction modifiers. One advantage straight 20 may have over ATF, however, is shear stability. Any modern (non synthetic) ATF is going to attain its working temp viscosity thru the use of polymeric VI improvers. These are subject the shearing. A straight 20 motor oil has no VI improvers, thus shearing is not an issue.

NB: Please understand that I'm talking about a straight 20 motor oil. It will be labeled as SAE 20, SAE 20W, or SAE 20W20. I am NOT suggesting the use of the more commonly available 5W20 motor oils in a Harley primary. Those are loaded with friction modifiers and VI improvers.

 

By "advantages" I'm assuming you mean the cost differental?

ATF is closer to a 10W and I don't know the composition of the new linings they are using, but assume they are compatible with 20-50W synthetic motor oil, since that's all they sell at the dealer for all 3 holes these days.

I've run ATF in my old bike with great results. I did get bit more external noise from the moving parts, but the friction discs loved it. After many hours of research, I found that "genuine" primary fluid was nothing more than hydraulic oil, type R&O... yep, just like you put in a farm tractor and I'll spare everyone the chemical properties, since I can't find my notes and hate typing anyway

Can't find that stuff around here except in 5 gal. and even then, it's not much difference price-wise from aftermarket "primary fluid" so I just run that. I mean, do the math - you only change it 3000 - 5000 miles plus once in the spring if it sits long. So, say you ride 15,000 miles a year, on a newer bike that only holds one quart, how much cash will you save by using generic ATF @ 2.19 a quart?

just my thought

 

Any modern ATF is the equivalent viscosity of 0w20 or 5w20 motor oil. Look up the specs for any modern ATF and you can see for yourself.

The primary advantage of using ATF or a straight 20 in the primary vs 20w50 or Formula+ is much smoother clutch engagement and less grab when cold. Also, with a lower viscosity fluid you're going to get less viscous drag on all primary components, most notably the chain.

 

Fluid used in the primary isn't under any type of 'stress', and it's only purpose is to control heat and splash lube the chain.

ATF type F works fine, and the same can be said of just about any other synthetic or dino fluid that says "Oil" on the container and has a moly content of <100 ppm.

I myself will stick with low cost Rotella T 15W40 as it's low cost, works perfectly, smooth shifts, and can be found just about anywhere you happen to be.

(BTW, it meets API Service CJ-4, CI-4 Plus, CH-4, CG-4, CF-4, SM, SL, SJ, and also JASO-MA for use in wet clutch applications).

 

To answer your question I took my bike in for service with redline MTL in the primary and Redline shockproof heavy gear oil in the trans. They asked if I want an oil change and I told them what I was running. The Service Manager told me most of the guys run TypeF ATF in their primarys and I could save a few bucks over the redline. I asked him about the HD primary oil and he said it is a straight 50w oil and most of the people he knows thinks it is too thick.

BTW, I was having warranty work done when I spoke with him. My dealer said the only time they would question what oil you use is if you didn't change it at the recommended intervals and upon disassembly there was evidence of sludge or severe heat distortion of parts indicating an oil failure.

 

I've used Harley's primary fluid, motor oils of various weights and red ATF and have never noticed any difference in performance, noise, feel or anything else. In the primary, it just doesn't much matter. I use red ATF so I know what's leaking.

 

I like the way you dealer thinks, unfortunately most have their head in the sand
Ron

 

What about the temperature limits that ATF has in a automatic trannsmition? I remember reading that the temperature of normal operation isn't that high, for example, at 170 deg. as being normal in a auto tranns, but at 185 deg. the atf fluid is near burnt and smells like toast... woulden't the 20 weight oil be able to handle the higher temps? I know when I'm riding 500 miles at 75mph in 90 deg. temps that my primary is still to hot to touch even after sitting for 5 hours,,, just a thought

 

Well, a modern ATF is the same viscosity as a 0w20 or 5w20 motor oil, so from that standpoint, no, a straight 20 would not be able to handle the heat better.

Your numbers are low regarding the operating temp of ATF and how high a temp ATF can take. I seriously doubt a Harley primary gets any hotter than the automatic transaxle in a modern front wheel drive car on a 90F summer day. Try sticking you hand on that and see how long you can hold it there.

 

Atf for all practical purposes is a life time fluid in automatic transmissions in regular cars which means it won't break down in normal use. Severe use may contaminate it beyond the filter capability as in trailer hauling but otherwise even some owners manuals claim it don't need changing in passenger cars. One of the most refined oils there is. Can't say that about regular oils. Many engines run in the 190 degree range, so the heat exchanger in the rad with trans oil will be that or more. The burnt smell you are referring to is fried clutch plates, not the oil itself.
Ron