Frosted glowplugs; am I my own worst enemy, running too lean?

**RknRusty** Tue Mar 06, 2012 9:33 am

I've been complaining about fouling glowplugs for a few months now. My original story is that my reedies started fouling plugs after running SIG fuel. I have run Glowplugboy 25% nitro/17% castor and never noticed a problem. After using the SIG, starting this past November, I started having plugs that won't light. Spraying them off with alcohol helps sometimes. I assumed it must be the fuel. But now I'm not sure.

After reading up on glowplugs and getting opinions on the forums, I'm finding other possibilities. PV Pilot said he learned from some old-timers that water in the fuel would do it. That's certainly possible, though I do keep mine tightly capped, out of the sun and cool whenever possible. I cap it between runs and changed out all of my syringes and fueling supplies. Paul Gibeault said it's possibly stray metal in my engines. This is possible because one of my Black Widows had a galled bearing journal and it was probably the one that fouled the most plugs. I thought my TD with a Nelson/Galbreath did not have the problem, but this morning I found it did. It had run poorly the last couple of times out, but I hadn't checked the plug and it apparently tolerated the problem longer than the Black Widows. It's been on a straight diet of SIG 35.

Now I read that running excessively lean causes it. When I fly, I always needle it so it runs fastest in the air, is that considered to be a lean run? It's 1/2A control line, that's the only way to fly. And the BW I've been rebuilding the past week frosted one of my new Cox cool inserts. I've been bench running it. I usually warm it up rich, but once it's been running for 20 seconds or so, I lean it out to full speed. The only time i go leaner is momentarily when I'm searching for peak.

So what about you guys that bench run, do you run full speed for several tanks while test running? No plug failures or frosting?

SuperDave Tue Mar 06, 2012 9:49 am

Rusty:

It is not all unusal to find water in some types of alcohol. What type were you using?

(Scotch doesn't count) Laughing

**Cribbs74** Tue Mar 06, 2012 9:54 am

Rusty,

It's been my experience that anything off of peak either rich or lean causes an audible drop in RPM. So If you tune by ear then chances are you are not going too lean. A tach would be the best way to peak an engine but, not practical in the field as you would burn through a tank before you perfected the RPM.

All I have ever used is Sig Champion fuel and I have never fouled or burned out a plug. I use 15% though. When it's gone I will go 25%.

35% nitro is harder on plugs than your GPB 25%

I think your frosting is fuel/nitro related. For what you are doing I think 25% would be more than adequate. Just my thoughts, not claiming to be an expert.

engine049 Tue Mar 06, 2012 9:57 am

I always added a small capfull of HEET to my fuel mix the ratios are up to you

It's the #1 selling gas-line antifreeze & water remover for fast starts in cold and resistance from harmful rust and corrosion. I Never killed a glow head.. I never really flew a lot either. But hey!

dankar04 Tue Mar 06, 2012 10:22 am

Might want to back off nitro and run them richer. Never peak them then fly. Frosting is good sign of lean runs. maybe add a little Klotz racing oil to mix.
Dan

John Goddard Tue Mar 06, 2012 12:43 pm

Don't forget the engines all lean out a bit in the air Rusty.
As for fuel can you not buy a little of the old stuff to see
If it eliminates prob?
Babe Bee

Paulgibeault Tue Mar 06, 2012 2:15 pm

HI Rusty,

First off, I run my Cox engines at full tilt regularly. Yes, over a period of time the plug elements will eventually 'frost'. Since I inspect them often, frosted plugs are changed. Although they still run OK, I think they may be on their way out.
HOWEVER, certainly one thing that accelerates this condition is being over compressed.
I've written before that the "rule -of-thumb" is one .005 shim per 10% of nitro in the fuel. Since it's a general rule, some engines may like a bit more or even less. I would try (in your case) adding one or more head shims & see how your engine runs. One record setting engine at a Nats (on 60% nitro) was frosting plugs seriously & needed six head shims to last a race. Shortly after the record setting flight, the crankshaft sheared in half. SO, I suspect the frosting was mostly caused by the (about to fail) crankshaft, which was starting to "make metal". Very difficult to spot until it's too late...
Keep at it!
Cheers, Paul

**RknRusty** Tue Mar 06, 2012 3:15 pm

SuperDave wrote:Rusty:

It is not all unusal to find water in some types of alcohol. What type were you using?

(Scotch doesn't count)

Methanol

cribbs74 wrote:Rusty,

It's been my experience that anything off of peak either rich or lean causes an audible drop in RPM. So If you tune by ear then chances are you are not going too lean. A tach would be the best way to peak an engine but, not practical in the field as you would burn through a tank before you perfected the RPM.

All I have ever used is Sig Champion fuel and I have never fouled or burned out a plug. I use 15% though. When it's gone I will go 25%.

35% nitro is harder on plugs than your GPB 25%

I think your frosting is fuel/nitro related. For what you are doing I think 25% would be more than adequate. Just my thoughts, not claiming to be an expert.

Except for a few tests with the SIG I always use Glowplugboy 24%/17%. I went out and bought castor oil today. I filtered my last 16 ounces of GPB, used the Excel mixture calculator I downloaded from Bernie and brought the oil up to 20%. It lowered the nitro to 22% but that should be fine.

engine049 wrote:I always added a small capfull of HEET to my fuel mix the ratios are up to you

It's the #1 selling gas-line antifreeze & water remover for fast starts in cold and resistance from harmful rust and corrosion. I Never killed a glow head.. I never really flew a lot either. But hey!

HEET is isopropanol. I didn't think it reacted with water any differently than methanol.

dankar04 wrote:Might want to back off nitro and run them richer. Never peak them then fly. Frosting is good sign of lean runs. maybe add a little Klotz racing oil to mix.Dan

John Goddard wrote:Don't forget the engines all lean out a bit in the air Rusty.
As for fuel can you not buy a little of the old stuff to see
If it eliminates prob?

I always find peak on the ground and back off a little rich from there, then launch. The engines peak in the air. Is that not the best way to fly c/l?

Paulgibeault wrote:HI Rusty,

First off, I run my Cox engines at full tilt regularly. Yes, over a period of time the plug elements will eventually 'frost'. Since I inspect them often, frosted plugs are changed. Although they still run OK, I think they may be on their way out.
HOWEVER, certainly one thing that accelerates this condition is being over compressed.
I've written before that the "rule -of-thumb" is one .005 shim per 10% of nitro in the fuel. Since it's a general rule, some engines may like a bit more or even less. I would try (in your case) adding one or more head shims & see how your engine runs. One record setting engine at a Nats (on 60% nitro) was frosting plugs seriously & needed six head shims to last a race. Shortly after the record setting flight, the crankshaft sheared in half. SO, I suspect the frosting was mostly caused by the (about to fail) crankshaft, which was starting to "make metal". Very difficult to spot until it's too late...
Keep at it!
Cheers, Paul

I'm new to high compression. Up until lately the TD with the N/G head/plug was my only high compression plug. I always run regular on the BWs. But now I have those very high comp head clamps and inserts from Bernie, and I'm running 5 shims.

Thanks for the answers and putting up with all of my questions, dudes. I'll keep plodding along and get it figured out. I'm going to keep using Glowplugboy, spiking each quart with 1.3 ounces of castor.That That makes it 23.1% nitro/20.1% castor. If I have no problems for a couple of months, I'll try some fresh SIG 25% again. I have no real use for 35% in the church yard across the street anyway. It was just my inner speed demon that bought that for the Tee Dee.

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