<VV> Snap Switch Temperature [long] - was: Engine Cooling

[Joel McGregor]

Excellent info.  Please let us know when you come up with a solution for your aftermarket gauges.  What results are you guys that have aftermarket gauges having?  Where are you reading temps?
Joel McGregor
________________________________________
At this
mounting position I discovered that the readings are always about 1/2 the
measured temperature of the factory gauge; 150-200F for most driving.  This
was the same for both VDO and Westach gauges using type J thermocouples
mounted to 110 heads.  It seems that the top surface of the snap switch
boss runs quite a bit cooler than the metal immediately under the quench
area or combustion chamber that the switch or thermistor senses.  I then
decided that an aircraft type thermocouple probe inserted in a hole drilled
somewhere in the snap switch boss would more likely yield the measurements
I was seeking.  I considered this route because I intend to use a dual
gauge on my new FC engine, yet I want to retain the snap switches [under
each head] both wired to the idiot light.  I looked at a 140 head that was
handy and noticed that a hole for such a probe could easily be drilled
parallel to the thermistor hole and that it would end up just under the top
edge of the quench area.  I placed a call to Ken Hand concerning this
idea.  He immediately pointed out that the switch/thermistor  boss on
140/turbo heads is different than all other heads.  Back in my shop I
located a spare 102 head and also looked at the head on a core 95
motor.  Sure enough, the boss designs are different!  In particular, the
turbo/140 boss is further inboard and higher up behind the end of the
combustion chamber with the mounting surface nestled between the fins,
whereas the standard [98/102/110] head boss extends lower down behind the
quench area with the snap switch mounted about even with the lower edge of
the fins.
Dale Dewald
Hancock, MI