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Glow Plug Life Expectancy

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Glow Plug Life Expectancy

Old 08-26-2008, 04:26 AM
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Default Glow Plug Life Expectancy

Glow Plugs. Not much cost individually but they are adding up. I have had to replace several glow plugs in all three OS engines recently. I am using OS plugs F and 8 as well as A5. On landing the engine will quit at idle or on restart the engine will not idle after removal of the glow driver to start. Fuel is 10% nitro which is the same for all three engines. Try not to lean out too much but aim for a solid top end RPM in flight.

Are these plugs getting more sensative to a hot run? Should they fail only on low end idle RPM's. If I take the plug out and apply the glow driver the coil still glows red. If I keep the revs up the engine will run OK. Sometimes its been one plug to a 10 min flight.

Any suggestions would be appreciated.

Keep em flying.
Old 08-26-2008, 06:52 AM
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Default RE: Glow Plug Life Expectancy

About the only flying modelers who expect less than long life out of glow plugs are racers. They know that their practice of setting for max rpm flight after flight is going to result in at best a slightly too lean run every so often.

Trying for high rpm and max performance usually means that you're needling the engine as close to flat out as you can, and if you're also using props with shorter diameters, you got two strikes before takeoff.

Max plugs seem to be as good as plugs get. There are others as good, but the point is, you got nothing wrong with your choice of plugs. Next is your 10% nitro fuel. Also nothing about 10% that shortens plug life. What's left? RPMs and lean runs.

Glow fuel two strokes depend on some amount of unburned fuel taking heat out as it goes. If your exhaust isn't showing fuel in it, the engine is probably seeing temps over what the mfg planned.

The beauty of our flying is that we can land right away and give the needle a click or two richer, takeoff after takeoff. Try an experiment. Set the needle as you normally do. Next plug that goes, put in a new one of the same type. Now set the needle as you normally do. Then give it two clicks richer and fly. Every time after that, when you reset the needle, set normally for you and then add two clicks richer. Chances are good that the airplane will actually fly with a bit more power AND that the plug will last longer than the airplane.
Old 08-26-2008, 07:33 AM
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Default RE: Glow Plug Life Expectancy

Just a thought - check your fuel before going too much further. I went through what I thought was a similar glow plug stint recently with my 46 LA and 46 AX, fresh fuel made all the difference. Now I'm extremely careful about ensuring the fuel can is sealed, haven't had a problem since.
Old 08-26-2008, 08:22 AM
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Default RE: Glow Plug Life Expectancy

Hmmm I have never see bad fuel cause glo plugs to blow, maybe the bad fuel was causing lean running. A lean tune is the number 1 cause of blown plugs. If set right a plug will last for quite a long time. I have a plane that has been using the same plug for two seasons.
Old 08-26-2008, 08:54 AM
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Default RE: Glow Plug Life Expectancy

Water in fuel will kill it on the spot[:@]
Old 08-26-2008, 09:29 AM
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Default RE: Glow Plug Life Expectancy

After a new engine break in I replace my Glow plug, and after a who season or two of flying. I change them like spark plugs... just not as often.

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Old 08-26-2008, 11:59 AM
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Default RE: Glow Plug Life Expectancy

I have had one glow plug stop working for no apparent reason in a very long time. They should easily go 2 flying seasons. Set your motor a touch on the rich side, your plug and your motor will last longer. I have toasted a couple over the years by plugging the glow starter wire in to the 12V port on the power panel. For some reason glow plugs don't like 12 volts...
Old 08-26-2008, 12:25 PM
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Default RE: Glow Plug Life Expectancy

I run my engines so that there is some smoke trail when the aircraft is in flight. This tells me I am not running the engine too lean. You said the glow plug still glowed red on your driver, yes a worn plug will still do that. Check the element in the plug if the coil looks at all deformed ( some coils tight and maybe one or two spread apart), if they are
the plug is either worn out or has had an overheat situation.

Old 08-26-2008, 06:32 PM
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Default RE: Glow Plug Life Expectancy

I have some engines that have been with the same plug for over 4 years, but I have an engine (ASP .61) which some time ago was running inverted and blow several plugs in the same season, I really do not know why, maybe the after run oil (transmission fluid) or something else, the fact is that I decided to change the position of the engine to a 90 degrees set up and solved the problem.

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