20w-50 Harley Sceamin Eagle oil is 2nd on the list of acceptable oils for this bike in the owners manual. Yes, it is full synthetic but that really shouldn’t matter. If anything the heavier weight should hold up a bit better than the 15w-50…especially since it’s been so hot in MA this summer. The oil was definitely broken down. Much thinner than I would have guessed for 2k old oil and darker in color (black coffee vs. amber). There was still some viscosity in the old oil, but less than I would like. YMMV but I will change the oil on this bike more frequently than I would with a lower revving engine.
I poked around on the H-D SIP site this morn (I have a subscription) and couldn't find any reference to semi-syn only. I did have below saved from last yr. Your dealer should say only semi-syn is recommended (mine does). After the debacle with checking oil levels (there's a TSB out for checking that supersedes the manuals), I really don't really trust their manuals lol. H-D oil service level is 5K miles, I am changing every 2,500 myself.
I had a 2 yr/15K mile PSP from my dealer, and my oil was changed every 2,500 miles. I used it up before the 2 years (am at almost 19K miles now, will own 2 yrs in Aug). I'm going to continue that every 2,500 mile service myself. I am currently using Shell Rotella T5 Syn blend 15W-40. API Service = CK-4, CJ-4, CI-4 Plus, CI-4 and CH-4. Mainly using this oil because I refuse to pay $14+a quart for H-D oil. I'll be changing my oil again around 20K and will see how it looks. Their T5 15W-40 is the highest weight I can find locally. Sam's Club sells it in 4 gal boxes and is a great deal, otherwise it is about $30ish a gal in auto parts stores. Advance Auto has it on sale right now for $24.99 per gal.
From the manual:
"If necessary and SYN-BLEND, SYN3,or HD 360 is not available, add oil certified for diesel engines. Acceptable designations include: CH-4, Cl-4 and CJ-4. The preferred viscosities, in descending order are: 20W50, 15W40 and10W40."
I'm curious what your mileage is and are you having any clutch slippage going on maybe that is causing the dark oil?
V/r
Jesse
