After taking my 85GL on a 1000mile trip I noticed my gas mileage shit the
bed. I was getting ~110miles per tank of gas on the highway. Two weeks ago I
was getting almost twice that.  Here are some observations..............
-strong exhaust smell
-badly surging idle
-my engine temp guage barely touches the bottom part of the coolant led
which makes me think the engine isn't running at      the proper temperature
-hesitation upon acceleration
-this morning, after I returned home and the van sat overnight I noticed
that my coolant overflow tank was almost full and the expansion tank was
down considerably

Part way through my trip I unplugged the O2 sensor to see if that was could
have added to the crappy mileage........I got the exact same mileage but the
van ran WAY better.........accelerated smoothly and would actually maintain
speed over some hills.....................

any thoughts as to where I should look first.............