Just adding confusion to this topic -
- the EK workshop manual indicates 226F (108C) for the temp switch. 
- and cross-checking Tridon - they call up a TTS033 part with a 125C spec. 
- and I was just given a Tridon TTS100 (supposedly from a red engine), but can't find any tech data on that part.
- grey motor info link http://www.fbekholden.com/forum/viewtopic.php?f=30&t=9856 also indicates TTS033.

Ciao, Tim

My grey motor had a water heater loop going from the front water exit hole on the cylinder head, through the heater core, back to an extra inlet on the water pump housing via a tap assembly.  Many years ago I just looped a hose from the head back to the pump as I was having problems with the heater core and the brass tap.  The rear water exit hole on the cylinder head has the tell-tale temperature sender. 

However this heater water loop effectively bypasses the thermostat and radiator core, and I am guessing I should really choke it down so that is justs acts like a bleed bypass, which should allow the engine to warm up at the nominal rate.  Does that make sense?

I note that the post (http://fefcholden.org.au/forum/index.php/topic,2066.0.html) highlighted that the rear of the cylinder head runs hotter than the front section.  Does anyone know the internal water flow path of the block and head?  I assume it comes up from the block as parallel paths into the head, and then joins up again - which would probably mean that the front of the head gets better water cooling as the flow rate would be better at the front due to a shorter water flow paths.

If that is the case then does it seem reasonable to take the heater loop from the head's rear hole.  That should allow an extra water flow rate through the rear section of the head - hopefully evening out the head temperature. I was also going to use the heater loop to insert an analog temperature sensor as that seemed a convenient point in the water flow path.
Ciao, Tim