Not just Harley's. I've heard this myth repeated with conviction among car wrenches too.

 

You lost everyone with the first six words of your question, good job.

Anyway, synthetic in all the things.

 

I meant downgrade in size, not quality!

 

Synthetic oils don't cause leaks, if you have synthetic oil and a leak somewhere, the issue isn't the oil.....something else it messed up (gasket, seals, crack, etc...). The reason you might see more leaking with synthetic oil is because if there is a problem, the synthetic oil will find it.

Since synthetic oils are "man made" the molecules are all identical whereas mineral oils and even blends contain a range of less precise and varying sizes of molecules. If one molecule in a 100% synthetic oil can find its way through an opening of some sort, then they all can.

Mineral and synthetic/mineral blends can actually help to plug up small openings because the varying sized molecules can act as a barrier, some of the smaller ones might get through, but once larger molecules start to back up on each other, they can then block out the smaller ones. It sounds nuts, but yes....it's true.

Another reason a person might experience some leaking when they switch to a full synthetic is because they typically use much better detergents. Those detergents might do to good of a job and begin to strip away carbon buildups that might have been plugging up potential leaking areas.

 

Bike looks good Smitty

 

Harleys don't leak they mark their territory.


I like the synthetic even though it's more expensive. Better oil better scoot?

 

Went synthetic all 3 holes and no leaks, all is good so far.
Thanks for all the feedback.

 

Synthetic Amsoil 20/50 in all three holes...no issues... I heard that the bike should be running cooler with synthetic over conventional...true or not..who knows for sure?

Sharp ride...congrats!

 

Classic!

 

Amsoil full synthetic. Just up graded pistons and cylinders. Mechanic said engine internally looked spotless. Oil change every 3000 miles. 2004 with 50,000 miles. Actually I've never seen or heard of anyone's bike marking there territory either.