QUESTION: Oil additives VS Oil brand?

[GAHorn]

In my opinion, the best way to avoid sticking valves is:

1. Confirm that valve-guides are reamed at rebuild to the proper clearances. (Using valves from a different mfr'r than the guides without confirming those tolerances is a set-up for problems. This sometimes occurs when factory-new cyls are obtained as incomplete assy's, or cyls are rebuilt and aftermarket valves are installed. I'm amazed at the number of times "field overhauls" are assembled without careful confirmation of clearances....new parts do NOT guarantee compatibilty.)

2. Use TCP with leaded fuel.

3. Stabilize engine temperatures before shut-down. (Avoid landing turn-offs and shut downs. Allow engines to idle at approx. 800-900 rpm for three minutes before shutdown.)

4. If the engine has not been started in a long time (several weeks or longer), pull the prop thru at least 6 revolutions (for a 6 cylinder) before attempting a start. This practice is one which has been virtually abandoned in modern times, and is unfortunate because it not only "limbers" and pre-lubes an engine, but it is an excellent pre-flight-inspection practice because (if done by hand) it allows the pilot to determine relative compressions among cylinders and listen for unusual noises. (or lack-therof, i.e., no "clicking" of impulse-couplings.) As always, be alert for the possibility of an engine-start. (Chocks and tail tied down, or brakes/ignition-educated occupant in the cockpit. (Another old-timer trick to limber an engine with less fear of starting is to pull the engine thru backwards but I don't like doing that because of the potential stress placed on generator and vacuum pump brushes when they're run in reverse.)
Some pilots motor the prop thru with the starter, but I do not feel that is as useful as doing it by hand for several reasons.... one cannot detect a "dead" cylinder as easily (an excellent opportunity is lost to detect no compression due to stuck valve).... and it drains the battery and heats the starter unnecessarily.
On an engine that is run regularly/recently I do not practice "limbering" an engine unless it is one I've not personally flown before. (If it is run regularly/recently it does not need limbering, however if it's one I've never flown, I like to determine relative compressions on all cylinders as part of my pre-flight.)

5. Use straight-weight engine oil. It "sticks" on parts of stationary engines longer. (Better for less wear/tear at start-up.... a thing Kas seems to forget he had promoted before he got consideration from the AvBlend folks.)

In 7,000 hours of reciprocating engine experience I've never had a stuck valve (knock on Ol' Gar's noggin) using those techniques. (Although I did have one in-flight once on a new engine that had improper valve-guide clearances. After they were properly reamed no further problem occured.)

[Showboatsix]

It sounds like a little "Marvel Mystery Oil" is needed in the gas. It works wonders in the round motors.

[GAHorn]

Marvel is no better than diesel fuel or jet fuel, which in gasoline is a contaminate, and creates carbon deposits. In the oil, it is a solvent which, once again, dilutes the oil and loosens sludge and therefore is bad for the interior of running engines.
I"d sooner add ordinary engine oil before I'd add MMO. (Besides the fact it'd be cheaper.)

[170C]

Regarding MMO--but George, MMO is pretty, red & smells pretty too (not as pretty, smell-wise as WD-40)

[Farnold]

I had a bad experience with the Exxon Elite in my 170. I had used it for one year then during a cold winter problems developed. I noticed that the breather tube was spitting out some thick crud that would not disperse into the ground like normal. It would sit there for weeks like a brown yellow glob. Then started the feeling that the a/c just was not performing adequately. Pressurized the crankcase with the resultant blowing out of a large glob of gunk with improved performance. Repeat scenario. Switched back to Phillips XC and no more problems. Now running Aeroshell straight in my 180 with no problems. I think that Elite just congealed in the crankcase. Only problem was that exceptionally cold winter for coastal New England. Other friends are still using Elite in their aircrafts. I would not recommend it in the O-300 however from my unscientific observation.