best fuel to use in cox engines

Thanks for the vote of confidence, John.
John is right, you must have castor for a Cox engine. The percentage of castor to synthetic and total oil content is argued to death on some forums. But 20% castor is guaranteed to suit the needs of a Cox engine. The piston and rod will die a violent death without it.

I've tried a few since Cox fuel disappeared. The best running fuel I've used is GlowPlugBoy Rocket 24 All Castor.
http://www.gcbmrc.com/GlowPlugBoy_prices.htm He has an eBay store too. Both take Paypal.
It has 24% nitromethane but only has 17% castor, so I go to the Dollar store and buy 2oz bottles of Rexall pure castor for $1.50. Adding 1.3 ounces to a quart will bring it up to 20% oil. Some say higher end castor causes less varnishing, so if you prefer, Klotz sells racing castor called Benol. http://www.klotzlube.com/Index.asp

The Rexall oil works fine for me. And I've used plain Glowplugboy with just the 17% oil with no trouble too, but I say play it safe and add the oil, I want my engines to last a long time.

Lots of people swear by Sig fuel which is half castor, half synthetic for a total oil content of 20%. I have tried their 20%, 25% and 35% nitro fuels and they never run any of my Coxes as smooth and easy to start as Glowplugboy. I have had Sig foul glowplugs if I flood an engine or run it very rich, something that happens often when I'm tinkering with one on the bench. And it make a greasy mess and stinks too. But that's only my opinion and experience. Others love the stuff.

You can run fuel with only 15% nitro, but I prefer 25%. For me, it seems to make starting easier and they run faster. For sport flying, I see no reason for higher nitro than that.

Ditto Rusty's post ! Go ahead and treat your Surestart to some good stuff ! Glowplugboy is a square, honest dude !!!!

Kim wrote:Ditto Rusty's post ! Go ahead and treat your Surestart to some good stuff ! Glowplugboy is a square, honest dude !!!!

I should also mention, he told me he would mix any combination of fuel I want if I'll buy 2 quarts (or was it 4, I forget). Shipping is either reduced or free after the first quart. I forgot that too. I usually get it 3 or 4 days after I order it.

I have been trying to get Sig 25% "1/2A" but that stuff has become hard to get recently (the guys at the rudest LHS refuse to stock it as they "have no reason to"). The best fuel I have used is Sig 25%. The last fuel I have been using is some Byron 25% with 16% all Castor. I added some extra Castor to bump it up to 20%.

Download this Guide

Sig Champion 25% (mentioned in the linked guide) is available mail order, in quarts. It is half castor/half synth. I have been using that in my PeeWee, QB, and TD .051 and starting seems fine (by hand, no spring or elec. starter). TD is a bit touchy, but I think that is just the nature of the beast.

They also bottle straight castor fuel, in 20% and 25% oil mixes, but 15% is the highest nitro content. OK for sport use, probably a little light for a TD. These are only available in gallons, so you get into hazmat shipping fees which more than doubles the cost.

Sig charges 9.95 for orders under $150, so it is kind of expensive just ordering fuel. But if you order a kit, bunch of hardware and couple quarts of fuel, the shipping offsets local sales tax (unless you live in IA).

Disclaimer: I sound kind of like a cheerleader in the above, but I am not now, nor have I ever been, an employee of Sig. Just nice to see one of the old line businesses still going and supplying the kind of stuff you can't get at the LTS anymore.

ahrma_581 wrote:Sig Champion 25% (mentioned in the linked guide) is available mail order, in quarts. It is half castor/half synth. I have been using that in my PeeWee, QB, and TD .051 and starting seems fine (by hand, no spring or elec. starter). TD is a bit touchy, but I think that is just the nature of the beast.

They also bottle straight castor fuel, in 20% and 25% oil mixes, but 15% is the highest nitro content. OK for sport use, probably a little light for a TD. These are only available in gallons, so you get into hazmat shipping fees which more than doubles the cost.

Sig charges 9.95 for orders under $150, so it is kind of expensive just ordering fuel. But if you order a kit, bunch of hardware and couple quarts of fuel, the shipping offsets local sales tax (unless you live in IA).

Disclaimer: I sound kind of like a cheerleader in the above, but I am not now, nor have I ever been, an employee of Sig. Just nice to see one of the old line businesses still going and supplying the kind of stuff you can't get at the LTS anymore.

Yeah, its the Champion 25 that I used to use before Hub Hobby quit stocking it. Actually, I think the reason they stopped stocking it is not only because they don't sell 1/2A engines anymore but the regulations have become stricter and the fire marshal limits them to so much. They mostly have helicopter fuel, car fuel and a small selection of airplane fuel now. They did have a bottle of Sig 100% castor to add to fuels but I believe they never restocked. When I bought that Bryon fuel, you had a pint of castor additive with some other extra crap added. They also had s little bottle of "Nitro Shot" extra nitromethane additive but I didn't get it to try.

Just my tuppence worth.
Over here there's a guy who will mix it to order which
Means you know it's fresh. It makes all the difference
Believe me.
If GPBoy offers to do the same over your side, he'd
Be my first port of call.

We send potential buyers to Glowplugboy (Mike) pretty well every day and have never heard anything detrimental about his fuel.

Cox engines should have between 15 and 22% oil and 1/2 can safely be synthetic; whereas the other 1/2 must be castor. Some racers use as little as 3-5% castor and 10% synthetic but engine life suffers. Those are the guys that use 60% nitro and budget 10 minutes per engine before rebuild.

so i got the engine up yo 285 degrees F
is that too hot?
also if i add caster oil would it be OK to run?
and if its OK where can i get caster oil?

cjuliano wrote:so i got the engine up yo 285 degrees F
is that too hot?
also if i add caster oil would it be OK to run?
and if its OK where can i get caster oil?

RknRusty wrote:...I go to the Dollar store and buy 2oz bottles of Rexall pure castor for $1.50. Adding 1.3 ounces to a quart will bring it up to 20% oil. Some say higher end castor causes less varnishing, so if you prefer, Klotz sells racing castor called Benol. http://www.klotzlube.com/Index.asp...

Or maybe a local motorcycle shop.

I don't know what the operating temperature of an .049 is, but I want to find out now.

I don't know what's in O'Donnel, but if it's just methanol, nitromethane and synthetic oil, you can toy with the mixture. When you get the formula figured out, the total oil should be 20% or more and half that should be castor.

Use the spreadshgeet here to calculate the mixture: www.coxengines.ca/files/castor.xls
If you have Excel, download it so you can use it without having to go online.

here is the link to the stuff i was using http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMGE6&P=ML
it says its for cars and trucks
so i was like ill just use this i don't know why it wouldn't work so i did
now people are telling me i can only use caster so now ill just by a new piston and sleeve.
that's another thing i love about these engines parts are cheap my car engine is $200 and a new sleeve is $95 i guess they mark it up.
kick as engine tho pulling 4.21 hp at 18,000 rpm practical. here is the link to that if you want to see it http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXXDA1&P=ML
its a Associated LRP ZR.30 X Competition.

cjuliano wrote:here is the link to the stuff i was using http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMGE6&P=ML
it says its for cars and trucks so i was like ill just use this i don't know why it wouldn't work so i did
now people are telling me i can only use caster so now ill just by a new piston and sleeve.

One of the characteristics of oil in bearings is that the oil tends to float the rotating surface in the center of the oil which provides a minimum of friction. Outside stresses will cause the rotating surface to touch and wear when those forces exceed the film strength of the lubricant (oil).

Another task of oil in glow engines is to carry off part of the heat of combustion. Under most conditions both synthetic and castor can handle the job. If your setting is too lean or firing time is off (controlled by compression, load, and fuel), the engine temperature can exceed normal tolerances. Under these conditions, most synthetics start to lose lubricating properties and burn as part of combustion, leaving nothing to lubricate, which causes temperature to spiral and cause excessive wear. This is called thermal runaway. The most often failure for this is the ball socket that holds the connecting rod to the piston because the ball is in direct contact with the hottest place in the engine...the piston top.

Castor on the other hand will create a varnish which will usually protect the engine but require a cleaning to remove the varnish in order to run well.

The 8% synthetic oil in the fuel you pointed to will allow the engine to wear out fast but get maximum performance. The choice is yours as to whether you want longer engine life.

Bear in mind that many truck and car engines have ball bearings an chrome cylinders (or nickel) with a high silicon/aluminum piston which have different wear characteristics from the aluminum sleeve bearing to crankshaft, and steel/steel piston/cylinder of Cox engines. The 20% figure that folks have provided is not arbitrary, it is from experience. Your choice whether to heed or not.

Good luck either way.

George

+1

Nice post, George.

George and I both come from a time when steel/steel construction was the norm and synthetic oils weren't around. Castor really played a big part in pulling heat out of the engine. With a lean hot run, castor polymerizes, forms long chain molecules, and continues to lubricate and dump heat. Synthetics start to burn, add to the heat problem and begin to fail. Synthetics have improved over the years, but if you read the tech sheets provided by Klotz Lubricants, castor still gets the nod for higher film strengths and higher flash points.

I run a castor/synthetic blend, but with about 21% total oil and 17% castor. That works out to around a 20/80 synthetic/castor ratio.

andrew