This test is
conducted to evaluate the condition of the glow plugs and to measure the 'on
time', which is controlled by the timer relay.
glow (or heater) plug will have a high initial current draw that will
gradually drop, stabilising at a constant amperage. The current draw will be
dependent on the wattage rating of the glow plug. This data is available in
the appropriate diesel data books.
the wattage has been ascertained, multiply it by the number of cylinders and
then divide by the voltage to calculate the expected stabilised current.
The length of
time that the glow plugs are operational can be measured from the initial drop
in current to the switch off point.
heater) plugs are utilised to aid cold starting, being activated in certain
engine conditions. The glow plugs can operate in several ways, the most simple
being switched on during cranking or while the ignition is switched on. The
glow plugs are wired in series and are fed with battery voltage for a set
period of time, which is determined by the 'glow plug timer relay'.
components soon heat to their operating temperature in a matter of seconds and
can seen to glow 'white hot' when tested out of the engine. The plug should
heat from the tip backwards, failure to do this means that the plug needs
systems may remain on until the engine's water temperature reaches a
predetermined temperature, while others may operate in a similar way but will
be pulsed alternatively in sets of two.
of the glow plugs can be achieved in one of two ways, by either leaving the
plugs in-situ and monitoring the current draw of them all, or by removing them
and analysing their performance visually as they heat up and measuring their
individual current draw, at the same time.