The 'S' in the MC FL-820S part number supposedly denotes the (S)ilicone anti-drainback valve vs the non-S FL-820. For sure, none of the crappy Frams sitting on the shelf next to the MC's have it.

Regardless, you cannot go wrong with factory spec parts. I've learned the hard way on that comment. It's the marketing that makes us want to buy the other stuff.

 

Holy crap! Is it bad enough that I should drain the oil and buy a new filter?

 

From what I've been told by my local Ford dealership, even if you are using full synthetic. Whether using Mobil 1 or Motorcraft you can mix synthetic and conventional blends of the same oil. I use Mobil 1 full synthetic 15,000 mile oil, either 0w-20w or 5w-20w. Every now and then I run short and have to top off with the same weight with a quart either in a syn blend or conventional. Knock wood, have never had any issues on any of my Fords, especially that top end clatter.

 

I assume you are being sarcastic? But no don't be silly what you have now is fine but just keep it in mind for future reference. In the early days these engines had severe dry start/piston slap issues and was leading to premature engine failure.The Motorcraft filter with the special anti drain back valve (silicone) solved the issue and it has been good since 2002 its why most of use will not stray from it.

Here is some side by side of the Mobil 1 and Supertech filters could not find the cut away but these filters are the same just one is 7.00 more and don't be fooled what looks like silicone in the Mobil 1 is not that has been checked before it is actually buna rubber that is colored red. Not sure why they went to that level of deception but it must be for a wow factor.

http://img357.imageshack.us/img357/1500/dsc03220fa5.jpg
^ Boxes side by side.

http://img76.imageshack.us/img76/5561/dsc03221be6.jpg
^ Supertech ST6607 on the left & Mobil 1 M1-108 on the right.

http://img181.imageshack.us/img181/4999/dsc03222ub3.jpg
^ Supertech ST6607 on the left & Mobil 1 M1-108 on the right.

http://img136.imageshack.us/img136/9748/dsc03223hn3.jpg
^ Supertech ST6607 on the left & Mobil 1 M1-108 on the right.

http://img357.imageshack.us/img357/6861/dsc03227cz3.jpg
^ Supertech ST6607 on the left & Mobil 1 M1-108 on the right.

http://img255.imageshack.us/img255/7558/dsc03225ke7.jpg
^ Mobil1 M1-108 closeup.

http://img76.imageshack.us/img76/884/dsc03226vp6.jpg
Supertech ST6607 closeup.

 

I was always told you shouldn't mix fossil and synthetic oils. I know there's alot of misinformation out there. Oil seems to be a real touchy subject for alot of people, you should hear the carrying on in the Harley forums. I always do scheduled routine maintanence on my vehicles...I just thought I'd get on the synthetic 5K miles schedule and save myself a few trips to wherever I'm having it done. I had an Ford Explorer that went 250,000+ miles on fossil oil having the oil changed every 3K miles. Buying synthetic for my bike and other cars that recommended synthetic, I thought it'd be easier just to stick to one brand, albeit different weights.