<VV> Cylinder head temp thermister

D. Monasterio dmonasterio at megared.net.mx
Sat Apr 19 18:41:26 EDT 2008


Frank,
   I think Dave is referring to the tinny threads (where the wire attaches) as the thermistor is installed so, there are no exposed grounded threads.
   If it is that way, resistance between tinny threads and ground may be in the thousands ohms range (room temp.). According to David Heiser info (provided on May 23rd, 2003), resistance at 200 deg. is 1,035 ohms, at 300 - 402, at 400 - 183, at 500 - 102 and at 600 deg.- 64 ohms. So, if Dave´s ohmmeter high range is 2K, it could show out of range at room's temp., for a good thermister.
   I remember have seen (and stored) a graph from Lew Rishell or Matt Nall showing full range thermister resistances but, I can't find it.

   Daniel

<<Since the thermistor is screwed into a hole in  the engine, there should 
be nearly ZERO resistance between the outside  thermistor threads and engine 
ground.  Think of the thermistor as a  variable resistance (varies inversely 
with temp) in series with the CHT  gauge.  +12 to +14 volts goes in one end of 
the wire to the gauge, out  the other end of the gauge, through a long wire in 
the tunnel to finally  connect to the center screwed tiny terminal of the 
thermistor.  From  there it goes through the varying resistor of the thermistor to 
the outer  shell and through the threads to the ground.  If I remember 
correctly,  the resistance of the thermistor at room temp is around 8000 ohms and 
drops  considerably as the temp increases.  So at room temp this high resistance 
 allows only a minimal amount of current to flow through the gauge barely  
moving the needle.  As the temp increases, the resistance decreases,  allowing 
more and more current to flow thereby raising the reading on the  gauge.>>


More information about the VirtualVairs mailing list