I agree to disagree.....m1 in all three holes has been done for years with zero ill effects....kinda blows that ''must '' wording out the window,down the street and into the sewer.

 

20w50 is motorcycle oil and good for all 3 holes if you'd like.

15w50 is car oil....bad news for a clutch.

On the bottle, the 15w50 says it's great for all "motorsports" and it has 'high zinc levels'. Perfect for the engine part of a Harley....but not the clutch/transmission.

The engine oil gets dirty fast, the clutch not as fast, the transmission takes a long time to dirty up.

My Routine:
$15 (1qt) Amsoil in the Transmission - change at 5000 miles.
$10 (1qt) Mobile1 20w50 in the clutch - change at ~2000 miles.
$4 (3qt) Mobile1 15w50 in the engine - change at ~2000 miles.

At 2000 miles, the oil is still good, but dirty...I run it through a home made filter system and reuse it in my lawn equipment and an old car.

 

Assuming you use the term clutch for the primary compartment, I wouldn't use 15-20 or 20 w -50 in there. esssentially a bath oil to keep the compensator and drive train quiet . I only use redline primary oil........I have no idea what the previous owner used but I can tell you it was old and dirty., amsoil is an excellant tranny choice btw.

 

the mobil v-twin has higher amounts of zinc and phosphorus in it than the 15-50 oil. do you need it ? maybe , maybe not, but i use the best oil i can find in my expensive truck and bike. cheapest thing you'll ever do to you bike is change oil.

 

The best test has been done by others on here, 15-50 works in these hogs. I've been using it long enough to say it works also, about 30,000 miles on bike with 108,000 on it. It's even cheaper if you get the rebate twice a year, can do up to 2 jugs at a time. Then it comes out to $3 a quart. I change often at these prices. Some think they get more if they spend more. And Bosch filter is awesome too.

 

I use NAPA 15w50 full Synthetic , made by the same folks that make Valvoline , l pay like $4.99 a quart. Unless I find a case of other 15w50 or 20w50 on clearance...

 

Bottom line:

Automotive oil and Motorcycle oil is not the exact same thing, regardless of what numbers are either side of the W. The question is "do you care"? If yes, pay for the MC oil, if no, save some $. When it comes to oil, you can spend 17 bux a quart or 2. According to the Internet, V-Twins are getting 100,000 mi either way. The less you care the more you save, and that's about it ! The proof; $2 a quart guys join oil threads only to crack wise, guys who spend $17 go on and on about minutia.

 

Kinda interesting that Briggs finally moved in to the current century and now recommends 15W50 syn for hot conditions.

 

If you're going to change often, why not just use conventional. The only thing synthetic has over conventional is length of service intervals. Engine protection is no better or worse. But if you're getting it cheap...
I change often too. That's why I run convenational in everything I own. Valvoline 5w30 in my car and Valvoline VR1 20W50 racing oil (high zinc) in the bike. Valvoline VR1 sae 50 in the primary. Harley's F+ is sae 50.
You wouldn't believe how clean the inside of the motor is on my 01 Bonneville SLE with 185,000 on it. 1500 miles on the oil and you still can barely see it on the dipstick it's so clean.

 

If that were true I'd go cheap too but it isn't. Best you just do a bit o Googling rather than me launching into a full Monte diatribe about the differences. There are many.