Question about Harley Davidson FLSTFI Fat Boy Motorcycles

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Oil type and weights for my fat boy - FLSTFI Fat Boy Harley Davidson Motorcycles

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Your bike came with H-D Syn 3 , 20W50 synthetic oil from the factory. You need to stay with 20W50 oil unless you live in some extremely cold or hot climate. For ambient temps running anywhere from 0° F. to 100° F., 20W50 is fine. You can use either petroleum based or synthetic oil. Other brands of oil that you can use are Mobil V-Twin, Amsoil, Revtech, and many others but go online and check for each manufacturer's recommendation. Harley says that you must use an oil that is rated for use in diesel engines due to the high pressure additives that these oil contain.

Good Luck

Posted on Apr 04, 2011

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How to convert standard to synthetic oil in all three chambers of a 2007 harley-davidson fat boy

Drain all the oils. Replace the oil filter. Fill all three cavities with synthetic oil.

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Feb 01, 2012 | 2003 Harley Davidson FLSTFI Fat Boy

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What is the proper weight of oil to use

depending on the temperature where you ride these are the listed weights
below 4 C (40 F).......10W40...starting below 10 C (50 F)...excellent
above 4 C (40 F).......20W50...starting below 10 C (50 F)...good
above 16 C (60 F)......SAE 50...starting below 10 C (50 F)...poor
above 27 C (80 F)......SAE 60...starting below 10 C (50 F)...poor

These weights are the recommended ones if the temperatures are basically constant.

hope this helps

Aug 27, 2011 | 2004 Harley Davidson FLSTF - FLSTFI Fat...

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What type of oil for the primary cover on 05 fat boy?

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Apr 07, 2011 | 2000 Harley Davidson FLSTF Fat boy

1 Answer


Three quarts of 20W50 oil

Good Luck

Jan 19, 2011 | 2003 Harley Davidson FLSTF Fat boy

1 Answer

I hit a medium size bump and hear a clanking noise in the forks

Well, this is not unusual, especially on the Fat Boy or the dressers. You've got a lot of stuff up there that will rattle if you hit a big enough bump.

It could be being caused by either too stiff of a fork assembly or too soft in the case of it bottoming out. Bottoming out is a dangerous situation. The way you change the "stiffness" of the front end is by change the viscosity of the fork oil. Most Harleys use "H-D type E" fork oil that is stated by most websites as being close to 30 weight. A 20 weight oil would make the forks "softer" while a heavier weight oil would make them "stiffer".

On dirt bikes, I've drilled additional holes in the damper rods inside the forks to give them quicker action and more bump dampening but I've never done it on a Big Harley.

Good Luck

Sep 23, 2010 | Harley Davidson FXDWG Dyna Wide Glide...

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Can't get my oil port open/off on my Fat Boy....To check it.

lightly heat the dip stick, then use a rag and longer pliers to gently but with power twist off = twist parallel to threads and be careful not to scratch. b blessed

Aug 01, 2010 | 2003 Harley Davidson FLSTFI Fat Boy

1 Answer

Right side where speed cable goes do i need oil its a 99 fat boy pulled plug no sigh of oil or anything

The '99 Fat Boy was equipped with the Evolution engine and five speed transmission. The TC88B engine wasn't introduced until the 2000 model in the Softail series. The speedometer cable should come from the front wheel. On the right side of the transmission, there is a plug and a cable going into it. This is the clutch cable. If you can't see any oil on the plug with the bike in the vertical position, you need to add oil. The transmission capacity is 20-24 ounces of Harley-Davidson semi-synthetic transmission lube or H-D Syn3. The drain plug is a Torx type pipe plug below the chrome cover on the right side.

Oct 14, 2009 | Harley Davidson FLSTFI Fat Boy Motorcycles

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