Applies to Late 1985 – 1991 Vanagons with 2.1 engine
Low coolant temperature readings on Vanagon after t-stat housing replacement.
On the van we were working on, the gauge was reading normal before replacement. After installing an anodized thermostat housing , the gauge read low when the cooling fan kicked on. The infrared temp gauge confirmed proper temp operation of the fan.
After testing the circuit we found the housing was not grounded, thus and incomplete circuit.
Solution A: for a fresh thermostat housing install
If t-stat aluminum housing is new, painted or anodized coated, the mounting surface and or threads for the temperature sensor (single pole) should be cleaned with sandpaper and thread tap before installation. The coated surfaces are non-conductive.
Solution B: if thermostat housing is installed on engine
If the thermostat housing is already on the engine, you can use a lock washer instead of the wavy or flat washers, on one of the mounting bolts. Once this was done the gauge reading returned to normal.