I listened in on the "all About Oil" webinar the other evening that was presented by Mike Busch, of "Savvy Aviator" fame - Google and check him out if you are not familiar with his credentials. Thought I would pass along some highlights from his presentation:
Mineral (petroleum-based) oil is better than synthetic oils with respect to suspension of particuates, and also seals better
Synthetic oils have superior (less) friction characteristics and are longer lasting than mineral oil.
As long as we are relying primarily on leaded avagas, we cant take advanage of the benefits of synthetic oils. Our engines run rather dirty, and the oil has to be drained often to get rid of lead and particulates. Also, the superior lubricity offered by synthetics is less important in piston aircraft due to the relatively large clearances and slow RPM compared to turbine engines.
Multigrade oil offers faster lubing during cold starts.
Monograde oil offers better corrosion protection, as it is not as thin at room temperatures and will stay on parts longer.
Corrosion is the #1 reason for failure to make TBO. There is very little wear during steady-state flight conditions. The longer an engine sits between starts, the more wear/corrosion will occur due to lack of oil on mvoing parts. Engines are typically not worn out, they are rusted out! Therefore, monograde oil is preferred over multigrade unless you anticipate unpreheated, subfreezing cold starts. Alternatively, you could use multigrade in the cold season only.
Aeroshell W100 is the recommended monograde; Phillips x/c 20W-50 for multigrade use
Aeroshell 15W50 is specifically NOT recommended; this is a 50% synthetic blend and will not be as effective in suspending/removing particulates
Ashless dispersants (AD oils) are in oils to suspend particulates. There is no evidence to indicate that engines do not break-in as well using AD oils.
"Microlon" / /"Slick 50" NOT recommended; a Teflon product that is potentially harmful according to a NASA study. Dupont, where Teflon wasdiscovered has specifically said that Teflon should not be used in oil
"Avblend": no harm, but no demonstrated benefit either
"ASL Camguard": Recommended! Some reduction in wear, but very effective in reducing corrosion, even more so than the additives that are included in the Aerosehll Plus and Exxon oils, although those are good as well.
"Lycoming 16702": An antiscuff, boundary layer additive, same as used in the Shell 15W-50/Exxon Elite products. Effective, although Mike prefers Camguard. Regardless, if you are using the Phillips x/c 20W-50 oil, use either Camguard or the 16702 additive.
"Marvel Mystery Oil": Some effectiveness in unsticking valve lifters and not harmful, but otherwise not recommended as a standard additive.
OIL LEVEL and CONSUMPTION
"normal" consumption is quite variable; 1 qt in 4-20 hours is fine; do not want less than this as it may mean oil is not circulating properly. No advantage to having full oil. Pay attention to changes in oil consumption however, as this could mean future problems
All engines will run fine at half of maximum oil capacity, and most at less than half. 2/3 capacity, or 5-6 qts in an 8 qt engine is recommended (8 qts in a 12 qt engine; 1 additional qt if your oil consumption is high.
Air-oil separators are NOT recommended; they can hide important symptoms regarding oil consumption and also makes it hard for engine to purge itself of acids etc.
If using spin-on oil filter, change oil at no more than 50 hrs or 4 months; change at 25 hrs or 4 months if only using a oil screen. If significant metal found at oil change, reduce to 15-20 hr intervals.
Try to not let the engine sit with dirty, old oil; change it before a period of disuse rather than after.
Cut open the oil filter at every oil change or least at each annual. A small quantity of metal, approximately 1/8 tsp. or less is normal; more than this should be investigated further
If significant metal is found, send in to lab for analysis (about $100). Aviation Laboratories in Kenner, LA is recommended.
Oil analysis for microscopic wear metals can provide early warning of wear events. Blackstone Labs in Ft. Wayne, Indiana is recommended.
Ideal oil temperature is 180-200F; definitely want it above 170 to boil off water. Temperature on gauge is typically the temperature of the oil during the coldest part of its circulation cycle; temperature is typically about 40 degrees higher at hottest part of cycle, hence the above 170 requirement. Since water boiling temperature decreases at higher elevations, lower temperatures may be ok at altitude.
If engine not to be run for 6 months or more, a preservative oil ("pickleing oil") is recommended. Fill sump with preservative oil; fly or run up engine and then shut down. Install dessicant plugs and place dessicant bags in air intakes and exhaust.
Pre-heating of engine to minimize wear at startup should be done any time temp is at 32F or lower. Starting without preheat at 20F or lower is a very severe wear event.
Lycomings are susceptible to wear on cams and lifters due to their high position on engine and difficulty in getting oil to these parts. Use of a Nay Nozzle (sp?) that squirts oil on cam shaft can help this. Installation of the nozzle would have to be done at engine build or upon tear down, but is relatively cheap and worthwhile.
Next webinar: "All About Cylinders", October 5 (free)
Mike can be reached for questions at firstname.lastname@example.org