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Thats because m1's v-twin syn oil isnt designed for or intended to be used in a diesel app in the 1st place.

I have been researching motor oil since 2006 for reasons i wont get into here but none the less have obtained a lot of info & experience of thats going on with motor oil along with also having 4.5 decades 1st hand exp restoring,wrenching & building motors in classic 60's-70's muscle cars & bikes too so have a decent back ground when it comes to wrenching motor etc along with the oil research too.

OK,15w-40 diesel oil thats most common isnt best choice for a lrg disp HD v-twin,but as HD states it is acceptable to use in the motor in a pinch which i feel isn't an issue short term either.

They did that because the 15w-40 D oil in the past all had decent anti wear/zddp of approx 1500ppm or so that protects air cooled HD's that run hot at times pretty good vs std pass car motor oil that on avg has a considerably lower 800-900ppm zddp lvl anti wear agent to prevent cat converters from premature failure causing emission & mfg/warranty issues.

People say/think the avg diesel oil like for ex chevron delo or retella 15w-40 doesn't contain a small amount of friction modifiers that arent so wet clutch friendly they do in fact contain them which is a fact got from oil engineers i spoke to from Chevron concerning Delo & shell 15w-40 diesel oil.

But,in a pinch chevron Delo 15w-40 has a decent 1300ppm zddp/anti wear agent lvl thats good for protecting motors against excessive heat etc ,shell rotella has approx 1150ppm which isnt quite as good an anti wear agent lvl.

approx 1200ppm or higher to max of 1800ppm zddp/anti wear agent lvl (long term) is very beneficial to protecting any lrg HD v-twin from scufing/scrtching/gailing in times of excessive heat cond's along with also being great protection for the valvetrain too.

But for guys still running cat's if your bike uses/burns any oil over many yrs/mile can poss foul a cat rendering it inoperable so keep that in mind when using oil that got over approx 800-1kppm zddp/anti wear agent lvl.

Bottom line is for what you spent to buy your HD why try to cheap out using not best choice or not proper oil for best protection in the motor/prim/trans of your expensive bike?

Will your HD self destruct any time soon if you run improper automotive/truck oil in all 3 holes,NO.

Is running oil specifically designed for HD v-wins,HD prim case & HD 6spd trans that only cost a few more bucks going to better protect it,YES.

I run Spectro oil specifically designed for lrg HD v-twins,i use either their semi blend or full syn 20w-50 in the motor,their 85w std dino prim oil in the prim case along with their full syn 75w-140 specifically designed for HD 6spd trans with great results.

1) I change the motor oil @ approx 3,500-4k miles vs HD's rec 5k miles.

With cam chain tensioner,cam bearing & even some lifter issues i figure proper fresher oil cant hurt because less friction with fresher proper less contaminated oil = less wear.

2) Change prim case oil @ either every motor oil & filter change or @ 5k miles max vs HD's 10k rec.

With compensator,prim chain adjuster,IPB issues etc ,again i figure proper fresher oil cant hurt because less friction with fresher proper less contaminated oil = less wear.

3) Change trans @ 10k miles or 1yr,which ever comes 1st vs HD's 20k rec.

With the general bearing issues HD has had in earlier 6spd trans again i figure proper fresher oil cant hurt because less friction with fresher proper less contaminated oil = less wear.

So some people may still wonder why i change the oil in all 3 holes earlier then HD recs'?

Thats simple,it's because ensuring there is always cleaner fresher oil with less dirt & contaminants in it thats properly formulated for application being used in (a motorcycle,not a car or truck!) should in theory extend srv'c life of all those components lubed by the fresher oil thats properly formulated for app it's used in.

But,THAT'S AS LONG AS THERE AREN'T ANY MFG ISSUES/DEFECTIVE PARTS IN THE MOTOR/PRIM CASE/TRANS AS RECEIVED NEW FROM HD IN WHICH CASE THEY ARE GOING FAIL PREMATURELY NO MATTER WHAT YOU DO.

Scott

 

Excellent post,
Unlike internet chatter and oil company marketing selling products with no true ratings at all. I do something different, I listen to the advice of the owners manual.

I run Mystik semi synthetic 15w50 diesel/gas oil, claims CJ4.
Mystik oil is well known in the heavy duty agriculture industry, it is a Citgo product, the same company that makes Harley Oil.

I suspect Harley is concerned about piston and ring cleanliness and why the CH4 or higher recommendation, Harley conventional 360 additive package is also similar to a diesel/gas oil.

Im unsure about pre Rushmore bikes, but the 103 HO engine sprays the bottom of the pistons with oil to help cool them and maybe why the call for the robust HEDO rating, to prevent piston and ring deposits.

I have also run MANY UOAs using Mystik, the last posted right in this forum under the UOA in the oil section, less the a week ago, also on bobistheoilguy.com

Ironically, this oil cost around $40 for a TWO GALLON jug delivered to my home, from ruralking.com.

Here is my UOA from just this week, I have run a total on FIVE UOA tests on my bike so far.
3 using Mystik and 2 HD 360 conventional.

Here is the link,
https://bobistheoilguy.com/forums/ub..._R#Post4483313

Im amazed that people pay $25,000 for a motorcycle and then ignore the oil requirements in the owners manual written by the people who built the engine, instead listen to unproven marketing crap from oil companies and well meaning people in internet forums.

 

Deleted, Double post to the above one. ...