Radiator and Injector fans

[spsherm@ibm.net]

I've got a couple of 5000CSTQ's, one just recently purchased.

One thing having the new one has made me notice, is that the newer one
runs noticibly cooler (on the dash temp gauge), and that the new TQ will
have the radiator fan and injector fan come on much sooner than my older
TQ.  The old one doesn't overheat, it just runs hotter and doesn't have
these fans coming on as soon.  

In fact I can't recall that the two lower radiator fan speeds ever come
on, on the older TQ, only the high speed.... and I can't recall the
injector fan ever coming on on the older one either...

I believe that all rad fan speeds work on the older TQ (a mechanic
recently checked them and reported that to me). So my question is... is
it the thermo sensor (the big 4/3 contact one) that controls all this
and would likely be responsible for no low or medium speed on the
radiator fan?  Would it also cause no injector fan?  If not what?

Other suggestions for things to check welcomed...

TIA

Steve