Carb/manifold heater

[what2do]

Lord only knows but I awoke early this morning and the following question popped into my fatigued head;
How efficient are carb/manifold heaters on dg's? My reason for asking is that they never seem to get a mention on here. They must fail at one point but I don't recall reading any posts where people have suspected their failure or anyone explaining how to test them. How would you know if they've packed up?

Just a thought, nothing more.

[itchyfeet]

I suspect many manifold heaters are not working but then again I suspect it's not really that important, it's only going to help in very cold conditions, (which we don't see much of )for a short while after startup.

to check use a multimeter set on ohms and measure the resistace from lead to the body with it disconnected, if open loop or very high resistance it's broke,

Just as likely the thermostatic switch or relay or wiring is also faulty and the heating element is OK so check that when cold straight after startup or with just ignition on you have 12V on the wire, and check when it's hot you don't have 12V on the wire.

the part load duct heater in the carb also powers from this circuit.

[kevtherev]

All the heaters are controlled by relay No. 1 in the junction box, and this relay is triggered by the thermo switch (temp 2) in the thermostat housing.
the heaters are set to turn off at 67 deg iirc