6
Why would fuel go “bad”?
The largest portion of the fuel is methanol (alcohol).
Methanol is hygroscopic; it attracts moisture. This can
cause your fuel to be contaminated with water, which will
cause poor engine performance. Additionally, the UV rays
in sunlight will eventually break down the nitromethane if
the fuel jug is stored in sunlight for long periods of time.
How can you tell when your fuel has gone “bad”?
The first indications will generally be the inability to start
the engines at previously run needle-valve settings.
Another clue might be that the engine has very poor idle,
runs but bogs down tremendously during run up and/or
will not attain the same rpms that you are used to.
How do I keep my fuel fresh?
If you have the opportunity, look for someone at a flying
field on a sunny day who has a jug of fuel that is only
1/4 full. What you may notice is that there are droplets
attached to the top and sides of the container. This is
the moisture in the air that is condensing inside the jug
because of the greenhouse effect of the semi-translucent
plastic jug. The only way to overcome the greenhouse
effect is to store your fuel in a metal can.
You can also combat the effects of the moisture in the air
by squeezing all the extra air from your fuel container at
the end of the day or transferring your fuel into smaller
containers as the level of the fuel is reduced in your
gallon jug. Many pilots will invest in 1/2 gallon or quart-
size containers and only bring that amount of fuel to the
field on any given day. This allows their main supply of
fuel to stay at home in a controlled storage environment,
virtually ensuring problem-free fuel.
How to tell if your glow plug is bad
The glow plugs on the market today are designed
to provide good service to the user and may last a long
time or a short time, all dependent upon the way you
choose to operate your engine.
Physical indications that you might need to change the
glow plug are:
1. Twisted or mangled glow plug element (usually
caused by too high a compression ratio).
2. Small “bumps” are attached to the glow plug
element. This will generally be most noticeable
during the break-in process. These are actually
tiny pieces of aluminum that have attached to the
element and will severely hinder the operation of
the glow plug.
3. The glow plug element is no longer shiny but is dull,
almost a white powder color. (This just comes with
age and is a by-product of the catalytic reaction.
The shinier the wire, the better the catalytic reaction
can be.)
Operating indications that you need to change your
glow plug are:
1. The glow element will not light with a charged glow
igniter. This indicates that there is a physical short
or breakage in the element wire itself.
2. Glow plug lights but the engine will not continue
running once the battery is disconnected. (This is
usually an indication of the microscopic particles
we discussed earlier.)
3. Glow plug lights, engine runs but there is a
perceptible loss of rpm at full throttle when the
battery is disconnected. This is a typical indication
that the white powder residue is building to the
point that the catalytic reaction of the glow plug is
no longer anywhere close to being optimum.
