Question: I noticed a few days ago some oil on the side of my oil tank just below the dipstick. It was just enough to make a film, and I guess it's leaking from the dipstick tube. My question is: I understand how the dipstick seal may allow some oil to leak past if the seal is damaged or has shrunk from heat, etc., but because the normal oil level is significantly lower than the top of the dipstick tube, how is the oil reaching the top of the tube to leak? Is it possible to get blow-by from the crankcase to the oil tank?

The dipstick is Harley aftermarket with temp indicator. I intend to replace it with the original (if I can find it) and use it this week to see if it makes any difference.

The bike is an 02 FLSTFI w/30,000mi., bought new.


And by the way, this is my first post, thanks in advance for you suggestions.

 

Bet this is oil coming from your crankcase breathers exiting through air filter. Pop off the air filter cover and you'll probably see some oil accumulated on bottom ridge. It's a common probable and oil overfill can make it worse.

Almost forgot welcome to the forum. You'll gain a lot of knowledge & good info here brotha!

 

Welcome. There is a lot of action happening in the oil tank with oil returning, steam etc, so all the oil tank surfaces will get a good coating. There is a small degree of crankcase vent impulsing that shows up in there as well. Breathers with umbrella valves (one way vents) vent it out in a controled fashion at the heads. It does take a slight pressure to open these so the pulses will show up in the tank too. At any time you reduce the air space on the top of the oil as in too much oil, or your rings are shot and blowby increases so does the pressure at the tank as the normal venting in the heads won't keep up. It will usually blow the dipstick out of the tank or fill the breather up with oil.
In your case the dipstick may not have enough pressure on the neoprene section to create a good enough seal. I also have the analogue type you have and it has less pressure than the oem when pushing it into the tank. It still doesn't leak, but yours may be damaged in the sealing area or it was too much undersize when new. I have not detected any amount of shrinkage with age, as it feels like it did when I first installed it 2 years ago.
Ron

 

Welcome Fatboy301. I think you'll like it here. There is so much to learn...
I too have the dipstick with temp gauge on it. After about 2 1/2-3 years, it started to leak down the side of my oil tank when riding. I found that the seal on it had gotten much looser over time. I replaced the dipstick with another one and the problem is fixed. Make sure that you aren't overfilling your oil, but the problem is probably just the seal on your dipstick.

 

Thanks everbidy, and to acchd: I took the air filter off just now, and there is a slight amount of oil on the bottom of the backing plate and filter lip, but not even enough to make a drip on the cam cover. I get more oil than this when I clean and re-oil my filter (yeah, I know, the knn oil is much thinner). Is some oil here normal? If my oil on the oil tank was coming from the breather, wouldn't I see evidence upstream from the oil tank also, maybe, like on the cylinder fins, or oil transfer lines? Not trying to knock down your suggestion at all, I agree its a likely culprit, I just don't want it to be. That means excessive blow-by, right? I'm gonna try the old dipstick and see how that works out. I'll let you know and thanks again for the prompt replies. Shiny side up and all that...

 

Normally you would see some drip on cam cover(directly below air cleaner cover) too so it could be the dipstick. I've had it blow back from filter onto the oil tank though and you see a splash of oil mist on the oil tank. Good luck with it and let us know it comes out!

 

Ok, problem solved, hopefully. I just went for a ride after installing the OE (unused) dipstick and no oil leak visible. I'll keep an eye on it this week to and from work. I did notice that the OE dipstick and the aftermarket Harley (analog temp indicator) dipstick are entirely different in the seal design. The OE stick has a plastic inner sleeve that uses an o-ring to seal against the dip tube, and the aftermarket is a ribbed plastic design which approximates the sealing action of really, three o-rings. The problem, in my opinion, is that the plastic used in the aftermarket piece has probably leached out all the plastisizer (softener) and become hard, and lost it's ability to seal. Just my two cents. Thanks for your comments.

 

I have the same problem with the H-D temp gauge dipstick. The original dipstick never did this. I returned the first temp gauge one I got because it leaked, but the new one does it too. I put the stock one back in and it doesn't leak. I too think the temp gauge one has a weaker seal. For $30 you'd think they could make something that doesn't leak.

 

Hey Fatboy301... Yeah... I had the same problem with the oil temp dipstick. I hadthe one with the Moco dial gauge, not the LCD one. Don't know which one you have. I brought it back and got a refund... piece of junk seal.

Hey... welcome.

 

Leaky dip stick huh? I had that once and had to go the the doctor for a shot!