cox glow heads losing their glow after some runs

balogh Tue May 14, 2013 2:12 pm

Gents,

anyone experiencing the same as I do? Some new COX glow heads light orange at the beginning of their lifetime but lose heat when connected to the same input voltage after say 1 hour of engine run. I run COX engines on max 25% nitro and make sure there are enough shims under the head to limit compression and save glow head from blowing.
I power the heads from a starter panel connected to the 12V battery of my car so the input voltage is constant. But after an hour or so engine run the head tends to lose its glowing capability under the same input voltage and does not even light up. The filament is intact - current still runs through it - and is center-located (no short-circuiting at its root), yet I have to dump many of the heads as they do not generate the heat required to start the engine.
The only difference to the new head I see is the cold filament becomes mat from its originally shiny look so I guess some oxidation may occur but I am not sure
Consulted Bernie of COX International who confirmed COX heads he sells today all come from the original OEM inventory so production specifications of heads are unchanged.

Maybe the problem is that starter panels have a reted output of 1,2Volts (designed for regular glow plugs that work also on rechargeable 1,2Volts AA batteries), that often suffices for new COX heads, which, though, are designed for 1,5Volts feed.

Your comments, please...

**RknRusty** Tue May 14, 2013 2:49 pm

A year or so ago I had a rash of Cox plugs turning white and frosty looking and would not glow, or only dimly, as you describe. At the time I blamed it on my Sig fuel, 25% and 35% nitromethane, and 50/50 oil. I bought new ones and only ran fuel with pure castor and they were fine, until I tried the Sig again, then the same thing happened. So I gave the Sig away and had no more problems.

Fast forward to a few months ago. I decided to give Sig another try and have used a couple of quarts of 25, 35 and 10% nitro with no problems. Soooo, that's not much of an answer is it. All I can figure is I may have had a production lot with some impurity in it that contaminated the plugs. Maybe you have some fuel that has something wrong in the mixture.

That's all I can offer, Balogh.

Rusty

SuperDave Tue May 14, 2013 3:40 pm

Balough:

I'd be suspicious of the power panel's output to the glo-head. Should be !.5 volts and no more.

SD

RAMJETT Thu May 16, 2013 7:12 pm

I would suspect the power panel voltage is marginal . your panel is likely voltage regulated ,having one that was current regulated would be better (I had sutch a panel years ago where you could adjust the output and you could see the current flow on a small amp meter on the panel, with this setup you can adjust current flow) The element in the plug is in fact a resistor ,after many heat cycles that resistance could change .if the resistance increases in the element it would require higher voltage at the glow the plug to pass the same current through the higher resistance . If you have a meter try to check the resistance on a new and used plug .or try a 1.5 v battery on a used plug to see if the higher voltage will in fact glow the plug. I just tested my theory and indeed after testing my new and used plugs they do show a difference . the used plugs all show .8 ohms and new plugs shoe 25% less resistance at .6 ohms. so a used plug would require 25% more voltage to have the same glow as a new plug. I tested 10 new plugs and 8 used plugs and they were all the same. .6 for new and .8 for used. Roger

crankbndr Thu May 16, 2013 8:46 pm

I clean my glow heads with this spray, but watch out it might shoot back in your eye. Not that I did that or something.

cox glow heads losing their glow after some runs Scan20

**RknRusty** Thu May 16, 2013 10:11 pm

Man, driveway mechanics are taking a big risk messing with the MAF sensor. Don't ever touch it with your hands or a rag or anything. The best thing you can do is look at it with your hands in your pockets. Change your air filter to keep it from getting dirty and don't mess with that laminar flow screen either. Just sayin'...

RAMJETT Fri May 17, 2013 5:55 pm

yep messing with a MAF is a big no no ,and a expensive lesson to learn. I like where it says on the can you will gain 4-10 mpg LOL . I wonder how they figure that ,seeing as the the 02 ultimately determines fuel mixture. granted at WOT or open loop conditions the MAF needs to be closely calibrated ,but the MAP has to be pretty whacked out for the block learn integrator not to be able to compensate . I guess this is like putting magnets on your fuel line to get better mileage LOL. Roger

crankbndr Fri May 17, 2013 6:04 pm

In my Fords the sensor is built into a cartridge that is easy to remove, they were dirty. The cleaning seemed to smooth the idle, no sweat, no problem.

SuperDave Fri May 17, 2013 6:32 pm

A "short snort" of aerosol fuel-injection cleaner on the MAF sure works to stabilize the idle on our Ford van. Not often just as needed.

SD

RAMJETT Fri May 17, 2013 8:28 pm

Spraying cleaner down the intake will clean the IAC motor and the throttle plate, this would indeed help Idle but not for the reason you are thinking. IAC motors and throttle plates are prone to carbon buildup and need cleaning once in a while. any cleaner you spray down the intake will be drawn through the IAC (idle air control ) and throttle plate and remove this carbon buildup, this will without a doubt help Idle. It's actually a very common service to clean the IAC motor and wash the throttle plate opening and set the base idle. the fact that the cleaner was sprayed on the MAF first would have little to with the change you are seeing , I would actually avoid spraying the MAF directly . also you should note that spraying cleaner down the intake could cause harm or failure to any exposed sensors, TPS / ACT / o2 /or cats/. you should remove a IAC or throttle body for cleaning to prevent cleaners from contaminating sensors or actuators . in the 30 years I have been a service tech I have never see the need to clean a MAF . the MAF has a heating element that burns off any foreign material prior to every start . in the early days so may TPS sensors were damaged as a result of the cleaners used for cleaning the throttle plates that it is required in all service manuals to remove TPS sensors when cleaning the throttle plates today .Roger

crankbndr Fri May 17, 2013 8:51 pm

Nevertheless, the spray cleans glow heads well and it dries instantly, leaves no residue. Which is why I posted it in the first place.

**RknRusty** Fri May 17, 2013 9:53 pm

Yep, sorry about the threadjack, Crank. I was just overcome by one of those spontaneous advice moments.

crankbndr Sat May 18, 2013 10:20 am

I like a good hijack, do it myself sometimes.

ekitten2 Mon May 20, 2013 2:39 am

if you like hijacking

https://www.youtube.com/watch?v=Tq6ugRIhuSg

balogh Sun May 26, 2013 7:51 am

crankbndr wrote:I clean my glow heads with this spray, but watch out it might shoot back in your eye. Not that I did that or something.

Matt - at Ex Model engines - sells refurbished COX glow heads on ebay (http://www.ebay.com/itm/Cox-049-302-1-Model-Airplane-Engine-Glow-Head-Refurbished-/271157510740?pt=US_Radio_Control_Control_Line&hash=item3f223f4254) , and explains the refurbishment means removal of castor residue burnt on the glow filament....I wonder what solvent he may use to remove the burnt castor that -if such refurbishment really helps reinstate the glow - may short-circuit the platinum filament thus letting the current flow through the burnt stuff rather than through the filament..

crankbndr Sun May 26, 2013 9:13 am

A few years ago an eBay seller was selling used car engines in lots of 99, I bought one lot. I found many in that lot to be like new and never fueled.
They had #1 Black Widow cylinders and the 302-1 glow heads. EX bought many lots, he may sell them as refurbished because they were removed from
the unfueled engines. Those cylinders and glow heads are a good deal at his prices, in my opinion.

cox glow heads losing their glow after some runs Img_0810

cox glow heads losing their glow after some runs Img_0910

balogh Wed Jun 12, 2013 4:29 pm

balogh wrote:Gents,

anyone experiencing the same as I do? Some new COX glow heads light orange at the beginning of their lifetime but lose heat when connected to the same input voltage after say 1 hour of engine run. I run COX engines on max 25% nitro and make sure there are enough shims under the head to limit compression and save glow head from blowing.
I power the heads from a starter panel connected to the 12V battery of my car so the input voltage is constant. But after an hour or so engine run the head tends to lose its glowing capability under the same input voltage and does not even light up. The filament is intact - current still runs through it - and is center-located (no short-circuiting at its root), yet I have to dump many of the heads as they do not generate the heat required to start the engine.
The only difference to the new head I see is the cold filament becomes mat from its originally shiny look so I guess some oxidation may occur but I am not sure
Consulted Bernie of COX International who confirmed COX heads he sells today all come from the original OEM inventory so production specifications of heads are unchanged.

Maybe the problem is that starter panels have a reted output of 1,2Volts (designed for regular glow plugs that work also on rechargeable 1,2Volts AA batteries), that often suffices for new COX heads, which, though, are designed for 1,5Volts feed.

Your comments, please...

Good news!!!

I ordered a Deluxe Panel II from Omnimodels that in principle has an output for the glow plug of 1,2 Volts only, but after it shipped and I tried I found it perfectly energizing the COX heads that have a rated input of 1,5 Volts. Even my oldest TeeDee head (virtually black inside from the castor varnish deposited after 10s of hours of run) glows bright when I turn the knob to grade 5 out of 6.

Just in case you want to abandon your 1,5Volts alkali batteries and use a panel connected to your car battery thru a cigar lighter and drive your electric starter as well, I recommend to all COX engine users...relatively cheap thing south of USD 30 when shipped even to Europe/Hungary from the US of A.

http://www3.omnimodels.com/cgi-bin/woi0001p?P=M&I=HCAP0302

EXModelEngines Wed Jun 12, 2013 4:41 pm

Looks like I missed this thread from a little less than a month ago, and wanted to clear up any lingering confusion.

The 'refurbished' glow heads are cleaned, yes, but not with a heavy 'carb-cleaner' solvent. We typically use an industrial De-greaser (sometimes diluted depending upon the part cleaning) to get most of the surface junk that may have been leftover off and then hand-check every glow head to ensure a strong glow. When cleaning the element in particular, fuel is squirted into the element chamber to loosen any gunk that may be trapped, then the glow head is again attached to the battery to check for proper use. The process is repeated as necessary. This is done to ensure at little 'rough-contact' as possible to the element (which is a very delicate part).

To be perfectly honest, these may not (and probably will not) have the full life of a new Cox glow head, but they are 50% off the price of a new one and in good shape. As crank mentioned they are derived from engines that have had light use. As always, if somebody was to purchase one and be unhappy with it, let me know and it will be replaced.

Matt

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cox glow heads losing their glow after some runs

cox glow heads losing their glow after some runs

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