I do engine and primary once a year. Synthetic in the motor. 15w40 Rotella in the primary. We ride about 6000 miles a yr. I do this late fall. The trans gets synthetic gear lube every other. I do replace the oil filter every 6 months.

 

Just for the heck of it . In the past I have run oil samples at 4-5 k just to see what they said. I had the resources to send them in cost me nothing but a little time.
What I found on the TC engines post 2007 was at 4-5 K the oil was fine. I still change it around 4-5 K on them .
Gave up on all that stuff now I just ride them and change oil and lubes when it is near the the time.
What I learned for all the messing around was. It really did not madder long as you ran a Quality oil.

 

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Good question.

HD motors(even newer SEMI cooled oil/water) have much more variance in op temp then the avg automotive engine does by a long shot which is much harder on the motor & oil itself too.

Its comparing apples to oranges as far as temp & op cond motor oil see's in the avg car or light truck vs an HD v-twin like for example riding 2up & bags fully loaded in summer heat cond & or when in traffic @ stoplights
,etc.

Here's what i do for my 09 FLHTCU & rec too:

* Motor oil & filter change using motorcycle specific oil (Spectro 20w-50) that has proper zddp/anti wear agent lvl to better protect hot running HD V-Twins and no friction modifiers that arent always wet clutch friendly.

HD rec's 5k miles,i do/rec 5k miles max on full syn,4k max on semi blend,3k max on std dino vs HD's 5k mile rec.

* Primary case,HD rec's 10k miles,i do/rec max of 5k miles using Spectro primary oil specifically formulated for HD prim case. So i generally change prim case oil @ same time i do motor oil & filter change.

* Trans.HD rec's 20k miles,i do/rec max 10k miles & or 1yr,which ever comes 1st using Spectro syn oil specifically formulated for HD trans which in my case in an 09 6spd.

BTW,i rec changing the oil earlier then HD rec's in all 3 holes for the following reasons:

* Motor,in my HD's motor no matter what mfg or type oil (syn/semi blend/std dino) i have used i notice when i get over 3k miles on std dino or semi blend i can hear/feel a diff in engine perf like valvetrain stats to make noise & hot oil pressure is a few lbs less across board too.

Using quality syn i notice that doesnt happen until i et approx 4k-4,500 or so miles on the oil so going 4k-5k miles on fully syn is ok.

* Primary case,the oil comes out horrible/stinky/black along with a ton of metallic and clutch fiber particles in it @ 10hd rec 10k mile change and when you have that much contamination in the oil it increases wear of all components in prim case lubed by that dirty oil laden with metallic & clutch particles.

But when changing it at 5k vs HD's rec 10k miles the oil doesnt stink/smell burnt but is still discolored / somewhat dirty but doesnt isnt pitch black with considerably less visual contamination in it too not near as bad as when when changing it at HD's 10k miles.

And we all know HD has had issues with compensators,IPB's,auto prim chain tensioners etc in prim case crapping out early so why take measures to help that situation keeping fresher oil in prim case.

* Trans ,HD recs 20k with can easily be 2-3yrs for the avg rider and i have noticed @ 20k miles the oil is sig discolored with some contam too,not horrible like prim case.

I figure since it's easy & cheap to change trans oil only being 1qt why not change it @ 10k miles or 1xyrly esp when some trans having had known bearing issues .

Bottom line is when you ensure there is always cleaner/fresher motorcycle specific oil in the motor/prim/trans of your HD doing so should extend srv'c of all those components .

But that's as long as there are no mfg defects from day 1 when bike was mfg'd and or wasnt bought used where oil maint may not have been done that often resulting in premature wear.

Scott

 

"I know a guy that never changed his oil"

That's most women I know. Had a GF about 25 years ago; we both h ad matching GMC Sportside PUs. She bought hers new;it had 25K on it without an oil change, mine had 8K when I bought it. Ran into her a couple years later, asked her how her truck was & she said "My engine blew".

Wonder how THAT happened?