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Author Topic: Caster oil and glow plugs.  (Read 908 times)

Online John Rist

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Caster oil and glow plugs.
« on: June 29, 2009, 12:35:48 PM »
Does caster oil kill glow plugs.  Since I have been running SIG all caster fuel in my ST G90 two OS F plugs have gone bad.  They will run as long as the glow driver is attached but the engine dies when you remove the glow driver.  This is a throttled engine on a scale aircraft.  I crank at 1/2 throttle let run for 10 -20 seconds and remove the driver.  With a new plug I get no rpm change when I remove it.  The last plug lasted 5 tank fulls.  What gives?  HB~>  Also do plugs have a platinum element or is it just platinum plating on a nichrome wire?
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Offline phil c

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Re: Caster oil and glow plugs.
« Reply #1 on: June 29, 2009, 04:58:54 PM »
Most plugs are platinum/iridium alloy(~$1400/oz).  I think Duke Fox discovered the iridium made the wire stronger at higher temperatures.

You can get buildup on the plug wire from castor oil and it does exactly what has happened to you.  It happens most often when you run the motor hard, and then the run finishes up going rich.  The rich run on a overheated plug can cause buildup on the wire.  Using Armorall(or similiar silicon antifoams) has also been blamed.

You can try burning off any buildup by carefully turning up your glow driver on the plug outside of the engine.  Gradually turn up the heat, but don't burn out the plug.  Of course, if you do nothing lost, since it wasn't working anyway.  Burning off the buildup may restore the plug to good running.  Most people don't bother though, since this kind of thing usually takes  a lot more than 5 runs to occur.
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phil Cartier

Offline RandySmith

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Re: Caster oil and glow plugs.
« Reply #2 on: June 29, 2009, 07:15:47 PM »
Quote from: John Rist on June 29, 2009, 12:35:48 PM
Does caster oil kill glow plugs.  Since I have been running SIG all caster fuel in my ST G90 two OS F plugs have gone bad.  They will run as long as the glow driver is attached but the engine dies when you remove the glow driver.  This is a throttled engine on a scale aircraft.  I crank at 1/2 throttle let run for 10 -20 seconds and remove the driver.  With a new plug I get no rpm change when I remove it.  The last plug lasted 5 tank fulls.  What gives?  HB~>  Also do plugs have a platinum element or is it just platinum plating on a nichrome wire?


Hi John

We have noticed a lot of "tater" build up, sort of brownish bumps growing on the element, These happen as often as 25 flights on heavy castor fuels, But I have never seen plugs go bad a 5 runs unless it has the element damaged from a super hot battery or high voltage.
The taters started happening about the same time castor manufacturing started using chemicals to extract more bean oil. I would suggest trying some other types of plugs

Randy
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Online John Rist

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Re: Caster oil and glow plugs.
« Reply #3 on: June 29, 2009, 07:29:54 PM »
Thanks all.  At least I am not going nuts.  I just change to a caster/synthetic 10% nitro (OMEGA fuel) and installed a new OS max #8 and got a great run.  I may try all synthetic.
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Offline ray copeland

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Re: Caster oil and glow plugs.
« Reply #4 on: June 29, 2009, 08:28:18 PM »
John, i have to confirm on my part the good qualities of Omega fuel , i use 15% nitro and add 10 ounces of castor and use OS #8 plugs mostly and some #A3  and get great runs on everything i fly, mostly os engines from .15 to .40 and 2 fox's, one .19 and one .35. I use Omega 25% in my dozen or so half a's that we fly.  Great runs and minimal castor buildup!!  y1
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Offline L0U CRANE

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Re: Caster oil and glow plugs.
« Reply #5 on: July 01, 2009, 03:43:36 PM »
John,

Another thing that's rough on glowplugs is excessive compression... You haven't mentioned how "hard" you run your G90; if you hear it crackling at wide open throttle (or "WOT") compression may be high. On many engines, such a condition has been cured by lower nitro fuel, or an added head gasket,or perhaps a slightly lighter prop load.

Also, I have no idea what orientation you have the engine mounted. If the engine is head down, or slanted down sidewinder, and you do a lot of mid- or low-throttle puttering around (and the mid-range is rich), you may be building up some castor in the upper cylinder.

What fuel is recommended for the G90? It might not like to run on an all-castor blend.

Luck!
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