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wrote:
My glowplugs don't and the engine heater light doesn't come on either,
though the engine starts quite happily with Easystart (don't like using

that too often)

What are the likely causes guys? There's a relay in the circuit called

an 'insulating relay & engine temperature relay, and an engine
temperature switch mounted in the thermostat housing.

I have a limited ability to follow circuits!

I'm not familiar with Lister engines specifically, but I'll base my
comments on the following assumptions:

1) Your engine uses glow plugs to preheat the combustion chamber to
facilitate cold weather starting.

2) Those plugs are activated when you switch on the key, and shut off
automatically when a sensor indicates the engine block or head has
reached a certain temperature.

The most likely point of failure in that system, and likely also the
cheapest and easiest to fix, will be the sensor (or "sending unit")
that is measuring the temperature of the block or head. The lack of
"engine preheat" indication at the helm could be due to a failure of
the sensor if the sensor. You should be able to put a wrench on the
unit, back it out, and replace it in a matter of several minutes and
the parts cost should be minimal. It could be something more complex,
but considering the cost to get a qualified marine electrician down to
your boat for a couple of hours swapping the sensor is a prudent first
step. (If it doesn't solve the problem, save the one you took out as a
spare).