MFTS and thermostat Q: Gauge not reading temp but HEAT

Henry A Harper III hah at
Tue Jan 11 15:12:09 EST 2005

> Phil & Kneale:
> Always good to hear from a few enthusiast and 200 20V owner.
> As Phil mentioned, I used Econ and felt warm enough thinking the air was
> venting to floor and Defrost.  I was quite surprised when HOT air
> came from the
> dash & console center vents when switched to Bi-Level.  (I always skipped
> Bi-level as I thought it would cycle the A/C compressor......old
> school KH 110 HP
> 4000Q I guess)

Hot air to the face means flapper motor malfunction to me. A/C compressor
will run (if ambient is above cutoff temp) in any mode except econ; bi-level
means cool air in the face and warmer air to the feet while other modes will
have one output air temp which should either be (mostly) in the defroster
and floor vents if output air temp is "warming up" the interior or (mostly)
dash vents if output air temp is "cooling off" the interior.

> No low coolant warning (just brake bulbs :-) ), but I was
> wondering if the
> thermostat was the cause or whether the coolant level wasn't as high as I
> believed (or air pocket).  Then expanding when hot to reach the MFTS.
> Let it idle and gauge reads fine (to 1/2 way) in about 10
> minutes.  Cold is
> fine on the track, but winter heat keeps the windows
> viewable/useable & safer.

I replaced a thermostat w/ sort-of-low-reading gauge and got hotter heat &
better fuel economy form faster warmup too. Conclusion: old thermostat
sticking open a bit or opening too soon. My derived rule of thumb would be
if your temp gauge goes down below the first individual line in cold-ambient
highway driving, and you are fairly confident of the multi-failure sensor,
it's time for a new thermostat. Temp gauge has thick lines at "cold" then a
short line which seems to be "thermostat opens temp", taller/thick line for
"normal", next line is "stage 2 fan turnon", next may be "hurricane mode
turnon" and then "time for new head" - no personal experience with the last

Henry by BOISE

More information about the 200q20v mailing list