If possible, can you pull over and get a reading with an infrared gun
after temp gauge drops?

I'd suggest confirming coolant temps at-near the temp sensors.

Disconnect the O2. See if fuel efficiency changes.  Check that the O2
signal wire isn't shorting to the outer ground sheathing.

a few images of those wires starting here:
https://picasaweb.google.com/musomuso/New1988Westy#5748856721901671282

Neil.

On Thu, Jan 24, 2013 at 9:26 AM, Craig Cowan <phishman068@gmail.com> wrote:

> Hello Gang!
> My '90 GL (Automatic) is giving me troubles.

> I had previously had a problem with the temp gauge never rising above 1/3
> on the gauge and it wouldn't make good heat. Of course I had a bad dash
> blower, so wasn't all that sure on the heat.
> Gas mileage was always bad. 14mpg max.
> Well last weekend I finally replaced the thermostat and things were looking
> good! The temp gauge would now read right in the middle, and with the new
> dash blower as well, i now had heat!
> But surprisingly, the gas mileage suffered still.
> Yesterday I filled up and found I had gotten 10.5mpg on that tank.
>
> Today I did some highway driving. This bus runs like a champ! Seriously
> good power, however I now see that the temp gauge will drop all the way to
> the bottom if I cruise at anything above 60mph. Anything below 50mph will
> maintain the temp gauge right in the middle, where it should be.
> I've never seen this happen. Any ideas?

--
Neil n

65 kb image Myford Ready For Assembly  http://tinyurl.com/64sx4rp

'88 Slate Blue Westy to be named.

'81 VanaJetta 2.0 "Jaco"  http://tubaneil.googlepages.com/

Vanagon VAG Gas I4/VR Swap Google Group:

http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines