Keith,
My layman's guess: with the engine running great, temperature stable, and good heat, you may be driving just a little harder than you were before the new thermostat. Not worried about the thermostat now, you feel comfortable opening her up a little more. Could be the difference between driving 72mph and driving 76 mph. That's what always seems to happen to me after a repair. YMMV
Don

----- Original Message -----
From: Keith Ovregaard <kovregaard@GMAIL.COM>
Date: Thursday, February 26, 2009 1:59 pm
Subject: Reduced Mileage

> Here's a question for the sage Vanagon mechanical volks out there:
>
> Anyone experience lower mileage after installing a new 87 degree
> (stock) thermostat? The average hwy MPG over the same 1300 mile trip
> went from 18.5 down to less than 16 since the new thermo was
> installed. The engine is running great and just passed smog with
> flying colors (with the new thermo). The temp gauge reads just above
> the LED with the new thermo (the old 80 degree thermo (lower than
> stock, but seems to be a common choice here in CA) ran just below the
> LED before it failed). The engine heats up really fast and the heater
> works much better (hotter & quicker). I would have thought these
> conditions would bode well for better mpg and a cleaner burning
> engine, but now I am skeptical. Does a hotter-running engine use more
> gas or could there be another cause that happened at the same time?
>
> Thanks in advance...
>
> Keith
> 90 Syncro westy VikingWagen
>