Electronic Thermo Switch and the CPU

[Dave Lawson <dlawson@digitalglobe.com>]

Mike writes,
>
1) ((Applies to 5K series)) Thanks to everyone who sent dead thermoswitches
for autopsy and possible reincarnation. Opening them up is not difficult -
just carefully pry back the brass crimping - use eye protection! - and slip
off the plastic cover. Could be resealed with epoxy or J-B weld, but not
worth the trouble.

Unfortunately, what's inside appears to be unrepairable: two pc boards, one
with a surface mount chip (utterly, totally unrepairable), and everything
soldered together in a dense mass.

Conclusion - even though some earlier posts have mentioned resoldering
several of the connections, unless you're REALLY bored, have NOTHING else to
do, and are hopelessly, terminally anal retentive, go buy a new sender. If
you look around, you can get them for about $40.

Functions of the sender are a) runs temp gauge, b) AC cutout if overheat, c)
runs overheat warning light. No connection to CPU, so no effect on startup
mixture, etc.
<

My documentation shows this electronic thermo switch contains an engine
temperature switch which is sampled by the CPU. If the coolant temperature
exceeds 119 degrees C (247 F), the wastegate frequency valve control system 
will not operate to prevent engine damage. It probably sets the WGFV DC to
0, so the WG upper chamber is connected to the intake air boot, thereby getting
vacuum and setting boost pressure to the minimum value.

If you bypass this switch or when using the Schrappnel Knobben, you should
be aware that you have eliminated an engine control system which helps prevent 
damage.
-
Dave Lawson