straight 50 weight in my Milwaukee 8

[alarmguy]

@silver1
The Harley M8 Engine has an oil cooler, actually quite large and you can also buy the Harley Accessory oil cooler fan and add that to the existing oil cooler.

Milwaukee-Eight Oil Cooler Fan 26800195 | Harley-Davidson USA

Find Milwaukee-Eight Oil Cooler Fan 26800195 at Harley-Davidson.com. Free shipping on orders $50+ and free returns.

www.harley-davidson.com

If it is the water cooled M8 I believe it does not have a cooler.

I think you're relying on misinformation regarding 325 oil temperatures unless you measured that yourself.

 

[thastinger]

I would probably just run M1 15-50 in it but you could go with some 25-40 marine engine oil if you wanted.

 

[BigCahuna]

I don't know where you can get a good full synthetic straight 50 motorcycle oil, just about all are 20w-50 and that's fine to use. I believe you can use 20w-60 as well.

SAE 60 Synthetic Motorcycle Oil

AMSOIL SAE 60 Motorcycle Oil features superior heat resistance and wear protection. Unlike others, it contains special anti-rust agents.

oilordering.com

 

[DriveHard]

I would probably just run M1 15-50 in it but you could go with some 25-40 marine engine oil if you wanted.

I would run M1 15w-50 as well. Run that in my bikes (below), and in my wife's KTM

 

[alarmguy]

deleted

 

[853okg]

I don't know where you can get a good full synthetic straight 50 motorcycle oil, just about all are 20w-50 and that's fine to use. I believe you can use 20w-60 as well.

Dennis Kirk sells straight 50w Klotz full synthetic for V twins. For what it’s worth.

 

[alarmguy]

HD 20w50 if you want to go by the book
or
15w50 HDEO if you want to sort of go by the book being its diesel rated
or
15w50 Mobile 1

Or any number of 20w50 oils, such as Mobile 1, Valvoline etc. motorcycle oil
No way would I use a straight weight oil
Adding an oil cooler is not going to help the heat you feel off the engine which you may know. It maybe help reduce oil temperatures a little but being you have a liquid cooled engine I doubt its critical, cant hurt but would be good for you to get an oil temperature gauge (if possible on an M8 to see if its needed.