synthetic engine oil for Lycoming engines?

[oscarm98]

I had someone mention to me the other day that they were going to use MobilOne Synthetic oil in their Lycoming O-235 because he had heard of someone else getting better Static and cruise RPM by using synthetic oil.

 

What is the general consensus on using Synthetic engine oil in these old technology engines?

[Waiter]

I don't know about the Synthetics, but I'll caution you about oil that to thin. I've been running Castrol GTX 20x50 in my Lyc since day one. At one point, I thought (Actually, I wasn't thinking at all) to use 5x30. Within 10 hours, I had a valve sticking.

 

Seems the thinner oil can more easily make its way between the valve steem and guide. It then cokes up and causes the valve to stick.

 

Waiter

[argoldman]

One of the reasons that using automotive oil is a no-no for aviation engines is the additives and the way that the detergent works. Aircraft engines (non-auto conversions) are rather loose fitting beasts and as such have more blow-by, etc. It is my understanding that aircraft oils handle this crap in a different way than automotive oils. I would assume that the automotive oils, be they synthetic or mineral have the same type of detergents in them and thus, other than the thinner lubricity, they act in an aircraft engine much like standard automotive oils do.

 

As a side note, Mobile 1 has been used in Rotary conversions with great success. However, there is no blow-by. I am led to believe that when oil change happens, the oil looks new.-- Perhaps that is rumor. However, on rebuild the main bearings seldom have to be replaced.