I am summarizing my practice based on Shell's information about minimizing corrosion in engines.   Protection from Aeroshell oil works for about two weeks which means to continue protection the engine should be run that often.  It does not appear to be proven that you need anything more than coating the surfaces so runups are fine as far as I can tell and flights are not needed for that protection to renew itself.

Corrosion from acid is the next problem.  Acid forms from combustion and increases with hours in oil.   Engines that sit should have clean oil to remove that corrosion factor.    Additionally, oil should be changed early so that acids can't accumulate.

My experience, backed up with oil analysis numbers, says running every two weeks minimum and leaving clean oil in for extended periods is the minimum.  Removing water with a dehydrator must be a positive addition but I don't believe it solves all the problems if the above recommendations haven't been implemented.

I currently use A/S W100, changed after 20 hours and I shoot for 25 maximum.  After 20 hours my wear numbers (ppm metal per hour) go up faster per hour than under 20 hours.  I found this relationship to hold true for the TSIO engines as well.  Leaving an engine unused one summer trashed my wear numbers and resulted in a call from the oil analysis folks.  Now, when I'm away I have someone run up the engine every two weeks, leave clean oil for extended periods away and have never had a flagged analysis since.  My experience with the multigrades is less positive than straight weight oil, particularly if multigrade is left in for more than 25 hours.  At 25 hours between changes, I found them to be similar except the A/S W100 (or W80 in winter) is far cheaper.

Paul
IO550 Legacy  720 TT


On 2013-07-03, at 11:49 AM, "William A. Hogarty" <billhogarty@gmail.com> wrote:

> Hi Colyn:
>  
> Not much use for an engine drier when the engine hasn't run since last August.
>  
> BUMMER