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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> Best oil content
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Best oil content - 5/17/2006 8:24:56 AM   
CARTERrc


 

Posts: 102
Joined: 12/5/2005
From: BundabergQueensland, AUSTRALIA
Status: offline 		G'day
What seems to be the best oil content in fuels for OS engines? I started off with 20% oil a mixture of 50% synthetic oil and 50% castor oil. Now have gone down to 15% oil both agin a 50/50 belnd of castor and synthetic and my engines seem to react extremely well to it. I believe that have gained 100-200 rpm out of the less oil. why would this be happening
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RE: Best oil content - 5/17/2006 9:45:25 AM   
XJet


 

Posts: 3464
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline 		Less oil means more methanol (in a given volume of fuel) and more methanol means more power. It's not actually that simple but basically oil doesn't add any energy to the combustion so it's reasonably true.

I would not be tempted to go below 18%-20% oil content on any modern 2-stroke (or 4-stroke) model aircraft glowplug engine (large SuperTigres excepted).

While you may well get away with a 15% oil content for some time, it will only take one lean run (due to a split fuel-line, air leak around the carby or whatever) and you could ruin your engine.

Rather than a 50/50 blend of synth/castor at 15%, I'd recommend that you go for a 80/20 blend of synth/castor run at 20%. This formula will give you 16% synth and 4% total oil in your mix. The small amount of castor will provide a huge margin of safety for your engine and the synth (being less viscous) will gain you a few hundred RPMs without sacrificing total oil content.

Modern engines will run on less oil, but not for very long -- just look at the short life of model/truck nitro engines where oil percentages are sometimes less than 10% and lifetimes are measured in a few short hours.

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RE: Best oil content - 5/17/2006 3:41:13 PM   
downunder



Posts: 3198
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline 		My personal preference is 20% oil for the majority of engines. For a bushed crankshaft I'd go up a bit more to 22%. If you want to experiment on using less oil then I'd suggest getting a thermocouple and checking the head temps. If it suddenly rises then you haven't got enough oil. But really I think it's false economy to go away from what's known to be a safe amount of oil because the cost of the small additional oil to go from 15% to 20% compared to the risk of quickly wearing out an expensive engine doesn't make it worthwhile.

You don't gain any power by reducing the oil content because the needle valve only tunes for whatever amount of methanol the engine needs. In other words, if you add oil then you open the needle slightly to account for it and let the same flow of methanol go through.

(in reply to XJet)
       Post #: 3

RE: Best oil content - 5/25/2006 2:44:15 AM   
howardflat


 

Posts: 15
Joined: 1/6/2005
From: Center Point, TX, USA
Status: offline 		I blend my own fuel, and use Klotz for the oil content. I use 16%, as per their instructions of using 15 to 18% total oil. If I were running store bought fuel, I'd run 18% as per OS's instructions. Generally the .60 sized and up engines can get away with less oil content, but I wouldn't want to risk it.

(in reply to downunder)
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RE: Best oil content - 5/30/2006 3:46:40 AM   
RaceCity



Posts: 1842
Joined: 7/10/2002
From: NotUpNorth, USA
Status: offline 		I also blend my own fuel and note closely that the oil percentages recommended by the engine manufactures are MINIMUMS. In light of this, 20% oil content by volume is a decades long standing, proven oil percentage that will work well, and provide good protection in virtually all modern engines. Whomever stated that it was "false economy" to scrimp on oil (even a few percent) was absolutely correct.

Also agreed with is Downunder's comment on oil content not reducing power. Unless taken to ridiculous extremes...he is very correct, and I have proven this to myself. One might fine tune the oil percentage for a given engine based on it's application, but top end power tends to remain unchanged.

If you're using good oils....a 20% oil/vol mixture will keep you, and your engine happy for many, many seasons.

"BEST" oil content? Probably no definitive answer to that since it depends on a number of factors, but using the engine mfrs recommended MINIMUM oil content as a guideline....you should be able to arrive at a suitable amount to use on your own.

< Message edited by RaceCity -- 5/30/2006 3:57:09 AM >

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