I was replacing the lowers on my FXSTC and while draining the R fork the oil ran out a dark brown color. In contrast the L fork was the exepcted Red color fliud. Also the amount from the R fork was probably about a oz less than the L fork.

A friend thought that maybe it was from water intrusion into the fork and the brown was from rust. I dont know about that. There is no leak on either fork. The dust and oil seals look good so Im not sure as to what caused the oil to turn browm.

I plan to check the fork oil after about 2K miles or so and see if it has changed color again. Anyone have any thoughts or experienced this before?

I bought the bike used (1yr) and this is the first fork oil change as far as I know.

 

Could very well be the previous owner did something.

 

Good idea to reinspect in 2K mileage.

Thoughts: Brown could be a fiber washer that is wearing. If grey I would be swaying toward a metal washer wearing - that color I have seen. Rust from water intrusion I am not sure as I would think you would find some oil traces at the spot it is leaking, yet possible. If you have airforks maybe water instrusion from the air compressor/ gas station air pump.

Did the previous owner install aftermarket springs? That would be major suspect as to what may have happened.

If brown again, I am sorry to write you have to more than likely remove and disassemble the fork to diagnose.

 

Fork oil cooks. A lot of people don't change it or change it enough. I would change it again and look at the color again in a few thousand miles or six months. Whichever comes first. You don't know if previous owner used two types of oil. This is what I do on both of my HD's. I change the fork oil twice a year. Might be overkill but the fork oil always looks and smells like it got real hot.

 

My left fork goes through seals about every 2 years. The oil in the left fork is black as used motor oil while the right fork is nice and red. The right fork seal holds up. There is no visible damage I can see with the left side but it is what it is for whatever reason. I deal with it and change them when it starts leaking.

 

Oil turns dark from contamination...normal. Do nothing unless your fork is leaking.

 

I'd change the fork oil again in about 5k miles to be sure. As others have said, the oil will heat up the more you ride and the more the oil is forced through the damper.

 

It is normal for it to turn color. Mine comes out black.

 

Update... 300ml came out of both. One fork had blood red oil, the other had brown and ran like water. Hahahahaha guess it was built on Friday. 2013 RG Custom, 1100 miles

 

Very likely there was a fork seal problem that was repaired by a dealer under warranty. They put new oil only in the side that was repaired which explains the difference in oil colors.
Happened to a bud and we found it when he came over to have me do some service maintenance for him.