Synthetic oil for GA air-cooled recip engines?

[PeteCO]

I seem to remember some uproar a few years back when a synthetic oil released into the market was allegedly causing all sorts of problems.

With the cost of a Lycon, and the great reputation of synthetic in other engines (and gearboxes, hydraulic systems etc) it makes sense to me that you'd want to run a synthetic lube whenever possible.

 

[troy]

the 15-50 oil we use at the FBO (can't remember the brand now) is already a syn blend. Nothing wrong with using syn oil, your engine will not know the difference.

 

[spngbobsqrpilot]

There was a problem with using a certain FULLY synthetic oil a "few" years back. I remember this as I was instucting at the time in a C150 and shortly (in less than 100 hours flight) after the boss (an A+P) switched to the 100% synth, the a/c would not make 5000' with instructor and student (this from the same a/c I had instructed in for years up to and immediately prior to the switch) and we could easily do 8500'+.Prior to the fully synthetic oil we had been using the 15W50 SEMI synthetic... an as I said, we never had an issue with the blend.


BTW, I did bring up the issue of decreasing performance... but I was "just a CFI" and the boss was "The A+P".

 

[avbug]

The oil will not limit the altitude to which you can climb. That's not the most ridiculous thing I've ever heard, but it's pretty darn close.

The ruckus about synthetic oil was with Mobil's ill fated Av1 effort a few years ago. That's gone away, isn't available, and isn't an issue. Almost as much fun as the Phillips XC saga, which wasn't synthetic, but did cause a lot of problems.

The current crop of semisynthetic offering is fine. More important is frequent oil change, which must be done regardless of the type of oil, and an ongoing spectrometric oil analysis program. While not the be-all and end-all of maintenance practices, it's a viable and useful tool for looking at engine health, whe properly applied.

 

[moving2vegas]

avbug- isn't there still an ongoing debate on sythetics among A&P's, especially when it concerns hardening of rubber components (seals)? Also, IMHO care should be used regarding engine times and synthetics. With new overhauls, just because you're through the mineral oil phase doesn't mean the break-in is over. It takes awhile to seat the rings completely and I've heard a number of A&P's say that synthetic works so well it can prevent the seating. What's your take?

 

[avbug]

Mostly bunk. The traditional thinking that mineral oil is necessary to seat rings doesn't hold too much water; many engines are broken in today using other oils, and a multi grade oil may be used just as well to break in an engine.

Always use the manufacturers recommendations.

As for concerns regarding hardening of seals, ridiculous. If the oil meets the appropriate Milspec, it meets the milspec. The oils aren't incompatible with seals, gaskets, etc. Synthetics tend to be more susceptible to find places to leak, but this isn't due to seal deterioration, but only to characteristics of the oil itself.

The only concerns with seating issues are glazing taking place before an adequate wear pattern has been established between the rings and cylinder walls. However, remember that the crosshatching that takes place during honing in cylinder refurbishment or production is a form of wearing in...glazing that takes place interrupts contact between the rings and the cylinder wall, resulting a poor seal, bypass, leakage, and increased oil consumption. that's more likely to occur with mineral oils (which include multi grade, single grade, and AD oils).

Remember also that "synthetic" oils and mineral oils come from the same source; they're all petroleum products. Many folks, mechanics included, believe that synthetic oil isn't really oil, but some made up product that's used in its place. Not so...all are petroleum products, just different formulations.

Mineral oils form glazing and deposits, whereas synthetics tend at the most to remove the deposits and glazing. Lacking the glazing, some minor increase in smoking may sometimes be seen, and may be misinterpreted to mean that "break-in" hasn't occured, when in fact, it has.