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Glenn, As for one company saying a competitor's product is better, of course not and that is not the question that I ask the oil co reps. BUT Aeroshell makes both types of oil, actually all three types and more. So you can ask the reps and also read their literature on lab tests as to how their Shell 15W-50w compares to straight 100w (50weight). Or Phillips 20w-50 versus their single weight. If you go to Sun N Fun the reps may give a seminar or at least be at their booth to talk to. I don't start my conversation with talk of Merlins or just 120 W, I look at what facts they have.
Obviously,they say the multi is better when cold, flows better throughout the engine, doesn't make the oil filter go into bypass, etc. BUT THEY ALSO SAY that the multi is better on the HOT end. If I have the terms right from memory, they say there is more shear strength in the more modern multis at the hot end. It is not just a matter of which oil seems thicker when sitting at room temperature, and not a matter of one brand over another.
As I said these are lab tests, not actual engine test runs. Also the co reps might just be biased toward selling the latest product, the multis. But I have also looked at similar lab tests by Aviation Consumer and found pretty much the same results.
If rust was the big problem, one can even use mineral oil, which leaves a protective coating inside the engine, that is why it looks so dirty, and it resist rust. Guys in England are still running mineral ok, and some are using 100 not 120.
I have not seen rust inside a Merlin after running, that is my personal experience with 1000 hours on my current Rolls model 76 run since major on Phillips 25w-60. Also my experience of the 550 hours on my previous 76 which began on mineral then switched to Aeroshell 120 w, mostly. I never saw, heard, or thought rust was a big problem. Same for a few minor oil leaks. The big problem as I know it is cam and follower wear, though to be mostly occuring on dry start ups, worse in cold weather.
Colorado is very dry, sometimes too dry for our skin and hair. Florida is a wet, salty corrosive atmosphere, so maybe rust is a problem there when just sitting. As for oil dripping off the cams when sitting, it sounds like the 120 w would be better, at first glance. BUT when you shut down a Merlin after flight the engine is very hot inside, any oil will be thin and run off. Even if one oil did linger on the cams better, is that sufficent to offset startup wear or do you need good oil flow asap above all else? I am not certain, both types of oil seem to work.
It would be rare but it can get cold in Florida. Years ago we came down to an event at Tittusville and it was in the 30s, I think , plus the wind. Colder than when I left Colorado.
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Bill Greenwood
Spitfire N308WK
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and we had added the Hinz filter a couple of years ago. The chip light on the Hinz unit may have saved the plane and pilot about 16 mos. ago, so we're real believers in that system. We're using Cross Country multi-vis oil in this engine and change it every 25 hrs. I just pulled the cowlings for an oil change last week and there was NO oil on the induction trunk (or any where else around the engine) so it's all staying inside.
