Synthetic vs Blend

Simple safe answer - use what your engine manufacturer recommends.

Some fuel companies say use blend for ABC engines and synthetic for ringed engines.

Magnum four strokes are ringed and the book specifically calls for castor in the fuel or you have no warranty. Saito four strokes are ABC or AAC and they recommend Cool Power Helicopter fuel which is all synthetic.

I like synthetic oils. My engine is a Thunder Tiger 61 Pro which is ABC/ABN, and the instructions call for castor oil. I do not run the engine extremely lean and it runs just fine with synthetic. The slime is easier to clean off of my plane than when I used blended oil.

Depends on the engine and type of use.

Morgan's, among others, recommends a blend for ABC/ABN engines, and straight castor for ringed or lapped iron engines. I've always followed this, and haven't have any trouble. Dr.1 Driver "There's a Hun in the sun!"

Straight castor for ringed engines? Not likely. They recommend straight synthetic (Cool Power) for ringed engines. I wouldn't recommend straight castor fuel for anything other than old iron piston, steel liner engines.

Interesting. My preference has always been castor/synthetic for ringed engines as well, though this is based on one particular experience. A friend of mine and I were running an ST .35 (broken in) on synthetic and it was unhappy no matter how much time was on it, needle fiddling etc. We switched to castor/synthetic blend, same mfg, same nitro content, and the motor immediately changed it's character totally, running stronger, consistently, throttling, idling better etc.

Beats me what other factors could account for that, but to us it was apples to apples and the difference plain as day.

As to straight castor - I agree, no way. That I would tend to think is one of those archaic "play it safe" manufacturer's suggestions harking back to lapped engines. Has it not been demonstrated by many knowledgable engine people that a certain percentage of castor is sufficient to provide the benefits without the horrors associated with pure castor?

Mike D.

Yup. That dates back to when Fox said use their fuel or void your warranty. Dr.1 Driver "There's a Hun in the sun!"

Mainly because if you DIDN't use their fuel, you would likely ruin their engines! They were so crudely made that they needed the 25% castor to keep the parts from grinding together.

We Ran all castor ( because thats all there was at the time ),in all our Mcoy and ETA ringed engines and never had a problem. I tried using it in a new Saito 130 twin and it did not like it at all. In my first YS120 i used a blend of 3% castor and 12% synthetic and never had a problem with sticking ring or carbon build up,motor ran for years on the original bearings and ring. DOUg

Agreed...we ran all castor in our ETA's, McCoy's, Doolings, MS29's...you name it. I ran 25% all castor in my Enya 45 for more years than I can remember and still use 25% in my ST G51. Not once have I ever had this so-called stuck ring problem. I use all castor in my ABC, ABN and AAC engines (all 2 strokes) because I KNOW it works.

I never had the stuck ring problem either, but the goop is certainly there. I have had to devarnish cylinder internals before though. I quite agree with the benefits of castor oil, but I'm pretty convinced that using a percentage of castor is sufficient and gives you some of the benfits of both types. I use 50/50 blend (20% total oil) in my 1/2A's and they run like a champ. I use lower percentages of castor in larger engines.

Mike D.

They weren't crudely made! Well OK the needles and carbs were, but the rest of the engines were well made. I have a Fox Stunt .35 that I have ran 100% synthetic oil on. Ran OK but hard to start afterward, not that the engine was overheated, its just that the thinner synthetic doesn't provide enough compression seal.

IMHO FOX engines were/are a "Curate's Egg" - meaning some parts are excellent. Others.. well.. ;-)

My old Hawk .60 ran like a bear, er, hawk. I liked the look of the tapered cylider fins, like that matters running-wise..

Mike D.

IMHO, the 'stuck ring' problem came from lean runs that burned the castor in the ring groove.

David

Castor has a lot higher flash point than synthetic oil. we used castor when thats the only oil for models, in ringed engines and never had a stuck ring. I used some Cool power 30% heli fuel which is all synthetic in a YS 63 4 stroke and after 3 gallons the valves were totally coked up with burnt on oil. DOUG

They were about the most crude looking engines I have ever owned. That says nothing about how they ran. All of mine ran great, once you understood Dukies' methodology.

If the synthetic oil was too thin, then there was WAAAAAAY too much clearance.

You didn't use the recommended fuel. What do you expect?

The only Fox engines that required castor oil was the lapped iron piston models. Duke claimed that the lifetime warrenty was void if synthetic was used on any of his engines. That didn't mean that they would not run on synthetic oil. He just did not like synthetic oil. I have a Fox Eagle from the 70's that I run occasionally on Omega fuel, that about 30% castor and 70% synthetic. It runs about as well as my K&B .61 and about the same weight but can be tricker to tune. Oh,and the finish is ugly.

I had an Eagle IV .74 that almost refused to run on anything but Duke's Fuel (10% nitro and 20% castor). Ran great on it and ran terrible on Powermaster.

It is rather strange that I got a gallon of Duke's Fuel that has a sticker on the top stating "100% synthetic". I still have the can with that sticker!

David