[V6-12v] Temp. gage reading low, trouble code 2312

[Tom Christiansen]

Folks,

The temp gage in my 1994 90S reads very low. On short drives (<15 min)
in the current 45-50 degree (F) weather the needle on the gage barely
makes it up to the minimum mark. Even after riding in stop-and-go
traffic for maybe 10-15 minutes followed by a short ride on the freeway
it usually doesn't make it higher than slightly below the second fat
mark at about 11 o'clock on the gage. On longer drives (one hour or so)
on the freeway the gage typically sits around or slightly above the
second small dot from the bottom. I have also been getting the 2312
trouble code indicating trouble with the Engine Coolant Temperature
sensor G62. I'm not 100% certain of the code number, but I am 110% sure
it was the ECT error code. The heat comes on before the needle reaches
the lower dot below the minimum mark on the gage.

I changed the ECT sensor. The sensor which was in the car (suspected
faulty) had an amber or brownish-orange 2-pin connector. The replacement
had a white connector. Don't know if there is a difference between the
two. I've thrown the old ECT away... While changing the thing, I cleaned
the connector.

I have paged through Bentley for procedures on how to test the ECT
sensor and the gage. I remember testing the new ECT sensor before I
installed it and it performed roughly like it should (the manual
mentions approximate values of resistance vs temperature, but I didn't
have a thermometer available to verify the ambient temp. I just
guessed...). 

For testing the gage, Bentley recommends messing around with ECT thermal
switch F76, which should be a 4-pin device located in the coolant line
behind the passenger's side cylinder head. I remember looking for this
without finding it at different time. Is Bentley on crack (wouldn't be
the first time!!) or have I just not looked hard enough? The only other
coolant temp. device I recall seeing is the huge thing in the bottom of
the radiator controlling the fan.

Any suggestions on how to drive this gremlin away? Is this an obvious
case of stuck open thermostat? Or is it more likely to be an electrical
issue?

If it turns out to be a thermostat issue, I suppose I'll need a new
thermostat and an o-ring (+ coolant). Are these dealer-only items or
should I shop around a bit? Any advantage/disadvantage of a non-OEM
thermostat?


Thanks,

	Tom