Oil viscosity
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Joined: Aug 2014
Posts: 63
Likes: 15
From: St. Petersburg, FL
You don't mention what year. For 2003 Softail, the manual states using 20w-50 (preferred), 15w-40 or 10w-40 in the crank case. It does not state the viscosities of the oils for the Primary or Transmission, only the HD part number. Some Harley dealers put the same oil in all 3 holes.
Tourer
Joined: Apr 2018
Posts: 280
Likes: 103
From: Manitoba
Road Master
Joined: Sep 2016
Posts: 1,048
Likes: 492
From: Heart of Georgia
Your manual doesn’t say because it really isn’t all that critical. Just don’t put gear oil in there. It tends to be too heavy. Some guys use 20w50 motor oil and some guys use ATF fluid. Me? I prefer primary chaincase oil since that’s what it’s for. Right now I’m running HD Formula +, which is basically straight 50w oil. I’ve used Lucas and Bel Ray in the past and can’t really tell any difference between those and the Formula +. Some people say you should avoid oils with extra friction modifiers because they can cause clutch slippage. Personally I just figure if it says primary chain case on the bottle I’m good to go regardless of the actual viscosity.
Last edited by blackxpress; May 28, 2018 at 03:01 PM.
Stellar HDF Member
Joined: Oct 2010
Posts: 2,594
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From: east texas
Same here in all my bikes, 30 years and still running
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Seasoned HDF Member
Joined: Nov 2009
Posts: 15,704
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From: Farmington ,MS
Been running gear oil in mine for 10 years, with no problems...really not critical
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