Hayden Adj Fan Switch
was to do something like the fan switch mod but
using a radiator-mounted thermostat. I even
went and bought a couple of Selco 170F, spade-
lug 'stats and potted one up in JB-Weld to make
it more weatherproof. These are pretty cheap and
high-enough current to run the relay coil if not
the fan directly.
Not adjustable like the Hayden, but it doesn't
really have to be - just need a setpoint below
your desired coolant temp by 10F or so.
As far as I've read, all of these fan mods run
the low speed fan only. You should set your high
speed fan in software to kick on about 3-5F above
where you see the thermostat holding temp in
normal driving (3F will let you hear the fans
after a hard run sometimes, 5F usually not).
The high speed fan will be your "backstop",
the thermostat (coolant) will be normally in
control, and the fan switch / radiator-mounted
'stat ensures the tank is cool enough to be useful.
It seems to me like the whole fan scheme could be
reworked with add-on relays to be more sensible
(like with a pair of staggered-temp tank-mounted
thermostats) but there's something about fault
codes from the fans that I don't understand
anything about. But I bet there's a way to fool
them, if done right with relay logic. Anybody have
the inside scoop on this aspect, let me know?




