Yes, most deviations must be self declared. SDMP works great and we have it on most of our aircraft. The maintenance organization where we do most maintenance could not care less.
You are lucky with the MO and with your MM contents 
Anyway, the point of this thread was whether going unleaded was really able to extend the service internal, and why. I suppose there is both the legal angle and the technical angle.
I would also add that decision to extend the oil change interval should very much depend on the oil condition itself.
Some engines have more blow-by some less. If you see that your oil becomes very dark or even black after 20-30 hours – replace it. It just became saturated with combustion products which heavily decrease its qualities.
Yes it would be interesting if those who use 91UL find their oil stays clean for much longer.
I always thought the oil going dark was due to combustion products, not lead in fuel.
Yes. The oil becomes dark from combustion products.
You will probably not see the lead inside it.
What I was saying is that is good to check the overall condition of your oil because even if there is no lead there may be still plenty of carbon products if the engine has blow – by.
A mate of mine brought a C150 and put 2000 hours on it with the last 1500 hours being solely on UL91 as at the time it was cheaper.
It was run in a school environment and was never leaned and it didn’t even had a oil filter just a screen.
I can’t remember much about the first 500 hours but after that it never missed a beat. No fouled plugs and not a single stuck exhaust valve. It needed one cylinder replacing but I can’t remember why as for the others they went all to TBO without work.
I would say without doubt the oil was cleaner. The silveriness that you get when the last dregs come out at an oil change were not there.
It was then sold to some kids who just ran it on Mogas and the engine did 4500 hours.
I know that’s only a sample size of one. But I have quite a lot of experience with O-200 it two other school environments which run on 100LL and they are plagued by sticking exhaust values and fouled and common. By and large all 4 cylinders will have been off reamed and lapped at under 1000 hours hours. Fortunately they usually then go all the way to TBO. With Superior lasting longer than Conti.
