Bobhend

My Feedback: (1)

The engine gurus in our club say that mixing of different brands of glow fuel can cause metallic precipitates that will destroy the platinum coating on a glow plug. I wonder if there is any hard knowlege that this is true ?One of my engines, an OS 61 FP would run very strong then die instantly, and i mean instantly. Much faster than if the fuel were suddenly pinched off. Something had to be causing the glow plug to not work. We replaced the glow plug and it ran fine. I did see a very tiny metallic looking sphere on the coil, an OS #8. We try our best to use the same fuels but for one reason or another [ LHS is out of stock for example] we end up with multiple fuels. We now will never mix fuels. Is this folklore or scientific fact ? Silicone RTV has also been mentioned by the gurus as doing the same plug killing if it is used to form an exhaust or intake gasket. Of course we know that metal from a failing part such as a bearing is a guaranteed way to kill a glow plug.

JCINTEXAS

No problem if you mix any of the good quality brand name fuels. You should pay attention to the nitro and oil percentages. Keep these the same, or at least within a close range. For instance, if you mix 2 or 3 different brands of fuel, and each has 10% nitro and 20% oil....your mix will still be 10% nitro and 20% oil. If you are blowing glowplugs, you are probably running too lean, or you may have small metal particles coming from a failing bearing.

Bobhend

My Feedback: (1)

The only time the mixing could have happened [not sure it even did] was in going from Omega 10 to Byron 10%. The OS 61 FP engine I don't think has race bearings. However, I am going to use only one fuel and if this happens again I will tear it down. I adjust the engines to be well on the rich side because they will lean out slightly in flight. I also doubt the guru's theory about mixing fuels but they are really convinced that RTV rubber, even on the exhaust manifold, can kill a plug. I use OS #8 and F and they always look perfect but there have been times when a new glow plug resoved a problem. I went electric to get away from these engine mysteries but tonight one of my motors developed loose magnets [ Hobbyking NTM Prop Drive series - AVOID !]. Putting an engine back on that plane ! Thanks, I knew I could count on you on this one.

JCINTEXAS

For several years I have been using PowerMaster and Byron's fuels. Nitro percentages vary depending on which engines I am running. In my OS 120AX and OS 46AX I run 10%. In my Mark 1.35 I run zero percent nitro (FAI) in hot weather and 5% nitro in the winter. Often I will pour fuel A left in one can into fuel B in another can, keeping the nitro percentage the same. No problemo. I do like to run smoky rich...probably an old habit from when I flew control line stunt models and Fox 35 engines waay back in the good old days. Anyway...I rarely have to change a glowplug.

JPMacG

My Feedback: (2)

Mixing fuels causing a problem sounds like folklore to me. But RTV contamination causing glow plug failure seems plausible.

There is not much that goes into glow fuel... methanol, castor or synthetic oil (or both), nitromethane, and some coloring. Maybe something is added to prevent foaming and maybe some proprietary snake oil ingredient is added so that a manufacturer can claim his product is better than the competition. I believe in the US the synthetic oil in model airplane fuels is the same among manufacturers.

1QwkSport2.5r

Whoever says mixing different fuel brands together will damage a glow plug is blowing hot air up your you-know-what. Unless there is an outside contaminant being introduced while mixing brand A and brand B together, it should have no effect on the glow plug. Provided you readjust both needles (or needle and airbleed in some cases) before beating the tar out of the engine on the new fuel will help keep the element from distorting from a lean mixture. If you go from using a fuel with more castor in it to a fuel with less castor in it, your mixture will be too lean and if you run up to WOT without adjusting the needle richer, you might burn the element up in the glow plug. The same can be said if going from a lower nitro fuel to a higher nitro fuel. Whenever I change fuel blends, I will almost always richen the main needle a 1/2 turn before firing the engine up just to be safe. Its always better to start too rich than too lean IMO.

I've used RTV silicone to seal backplates, exhaust systems, and the bottom of carbs for years without ever having a glow plug fail because of it. I mix all of my own fuel for all of my engines as well and in certain circumstances I will add a little Armorall original to my car fuel to keep fuel bubbling minimized. The fuel tanks in cars are mounted rigid and there is usually no way to isolate the tank from the chassis so bubbles are inevitable. I've also used silicone shock oil for rc cars in fuel to minimize bubbles and that didnt cause a plug failure either, it just didnt work as well as armorall oddly enough..

Bobhend

My Feedback: (1)

Sounds about right to me. Thanks for your first-hand data. It is a full time job in this hobby sorting facts from all the information volunteered by the witch doctors at the field.

1QwkSport2.5r

Sometimes you just need to try things for yourself to find out. I remember being told that a rc car engine will not run anywhere remotely close to right on airplane fuel and I'll overheat it from too much oil. I ran a few different kinds of airplane fuel in one of my 1/8th scale monster trucks with a .28 engine and it ran cooler with the airplane fuel than it did with car fuel. It did get a soggier bottom end (took a little longer to clean out) and the top rpm was down some but it ran fine for a backyard basher. I even tried 5% nitro 25% castor for a tank when I broke in a .20 car engine and it ran just fine. No instant gratification with all the extra oil, but I had to try it to bust the myth people tried forcing down my throat that it would overheat.

I'm glad you asked the question about it... Sounds like your field guru needs to go do some research and fix his facts.. I'll add one more thing... AFAIK, the platinum wire in a glow plug isnt plated, its an alloy.

Bobhend

My Feedback: (1)

You are right, according to the wiki http://en.wikipedia.org/wiki/Glow_plug_(model_engine) it is a platinum wire alloyed with something else. This is great news because loss of surface material will not be missed and the plug should go on working until the wire actually breaks or shorts. This means that all the times I have "solved a problem by putting in a new glow plug" it probably would have cleared up eventually. Glad I kept the ones I took out ! I have found that the OS F and #8 keep their shape and look good for a very long time. With the A3 [now called #6] I had many of them develop shorts in the coils, probably due to running too lean. These collapsed A3 plugs would draw over 5 amps which my RCAT Systems glow driver could not do, and the 5 A may have also contributed to the demise of two Tower nicad glow drivers with the current meter built in.

I did a little more reading. Evidently the platinum probably contains 2 - 8 % tungsten but the exact formula is a trade secret. I found some mention of plated glow plugs being made in the past but evidently all quality glow plugs are solid platinum alloy wire. I plan to stick with OS forever.

1QwkSport2.5r

Well, over time the plugs element can get fouled from combustion. If you look at a new plug and a plug with 5 gallons on it, you will see the used plug will have a frosted appearance to it. If the wire is gray and frosted and your engine runs funky, it could be that the platinum wire has enough of a coating of combustion byproducts that it cant keep a good catalytic reaction going. Some plugs will glow nice and bright but will not fire an engine off to save its life. Glow plugs do not last forever, unfortunately. If an engine begins running erratically, eliminating the carburetor/fuel system from debris/dirt/obstructions would be my first choice, followed by ensuring all screws are tight. Being that glow plugs are on average $8 each and higher, I only replace a plug if it looks frosted or the coils are distorted/melted/collapsed.

I'll add my 2 cents on brand name glow plugs - I do not use OS plugs. I think they are overpriced and in my experiences, underperform. I have one OS glow plug, a Type F, in an Enya 4-stroke engine. It works well enough, but my Fox idle bar plugs ($5 each) give better top rpm in this engine than the type F. Moreover, I use McCoy MC59 (hot) plugs in every other engine I own and run from .20 car engines on 20% nitro all the way up to my SuperTigre S90K on 5% nitro. I got a whole card of 12 plugs for about $5.50 per plug. These usually last me a gallon or two in my car engines (again, 20% nitro) and 3-4 gallons+ in my airplane engines. They are long reach plugs which most of my engines call for. Most OS plugs are medium reach and cost a lot more. I'm not a big fan of them personally.

Tungsten is one metal they alloy with platinum as well as other precious metals like iridium and even more exotic metals like paladium and byrillium. Generally though, most quality glow plugs will be an allow and not plated. Many guys really like OS plugs, and are willing to pay the price for them. I am not one of those guys. My cheapo McCoy's work great for me.

I'm off my OS rant now. You use what you like and can afford. They work fine, but IMO, there are others that work as well or better for a lower cost.

Jim Thomerson

Glow plugs can go bad. When I pull a plug which still glows, I put it in a film canister with other small parts. From time to time when bench running an engine, I will need a plug, and take an old one out of the cannister. They run fine. I don't know what happens in the cannister (it is dark in there). Maybe the coating oxidizes off or something. Back when we were doing control line racing, we used GloBee plugs, a new one for each race. They would grow bumps, called 'taters' on the element.
We ran the old plugs in practice.

JCINTEXAS

I have used many different brands of plugs over the years. For the past 2 years, I've been using the Sig plugs with the idlebar. They perform very well.

1QwkSport2.5r

I save all of my old plugs for breaking in new engines and save the new ones for everyday running. If an engine will not run on them at a lean setting without the glow driver I pitch them in the trash. If the element gets distorted I also pitch them.

downunder

The platinum is usually alloyed with either iridium or rhodium which are from the platinum family of metals. Pure platinum is rather soft so these other metals mainly give strength to the coil but they also make it capable of handling much higher temperatures. The plug manufacturers just buy coils of the wire from distributors but different manufacturers of the wire will have their own particular alloys.

I heard a story about Gordon Burford (he made the Taipan etc engines) who wondered why all his plug wire was disappearing. Eventually he found out that one of the guys in his factory was using it to bind pieces of wire together for soldering. He kept it locked up in a safe after that .

Sport_Pilot

Idiotic! Silicone and Silicon are not the same! The latter is a metal and it might do damage to plugs and a lot of wear on the metal parts as well. Silicone is not a metal and causes no harm.

Sport_Pilot

The metal is wear from the bearings from the low oil content from the oil. A sleved bearing should be using 20% oil with mostly (preferably all) castor. Those fuels do no have enough oil!

Sport_Pilot

LOL, gold wire would work well too! And would probably be cheaper!

Bobhend

My Feedback: (1)

Here is a recent post discussing silicone liquid anti-foaming agent contaminating glow plugs. http://www.rcgroups.com/forums/showt...1661195&page=4[last post]. Note if anyone mentioned silicon [sand] it was probably a typo. I cannot find any definitive test work and doubt we ever will. I plan to avoid having RTV anywhere on my engines, based soley on erring on the side of caution. In other words the next time I have an engine mystery I will know one thing that was not the cause.

countilaw

I think running too lean and over heating is the biggest culprit to blowing plugs. I also believe that too much silicone in the fuel will contaminate the plug. But in most cases, the contamination will burn off.

Frank