Temperature Gauge Adapter
Fits 46-51 Truck, Station Wagon with 4-134 motor

Temperature Gauge Adapter

The 1946 through mid-1950 Willys-Overland 4WD and 2WD Trucks, Station Wagons, Sedan-deliveries and Jeepsters with the L-134 engine used a "square" instrument cluster arrangement.

1946 - 1950 1/2, Instrument Cluster Configuration

The fuel, oil and temperature gauges were King-Seeley thermal gauges. An internal bi-metal strip heats up and the needle moves. The fuel and oil gauges are "right side up" gauges.  With the ignition key off, they rest at the left end of the scale. But, the temperature gauge is mounted upside down - with the key off it rests at the right end of the scale. With the key on, it swings to the left- the cold end of the scale.

In mid-1950, when Willys-Overland introduced the F-134 engine into their trucks, they changed the instrument cluster to the "clock and bar" arrangement, the temperature gauge became a 'right-side-up" gauge like the fuel and oil gauges.

Later Instrument Cluster Configuration

This styling change, which made the temperature gauge a 'right-side-up" gauge, required the "plug - heat indicator"- as Willys-Overland called the engine temperature sensor - to change as well. In the early version of cluster, the gauge had to heat to move the needle to the cold indication. In the later version, the gauge heated up to move to the hot indication.  

Over the years it was not uncommon for the early trucks, wagons and sedan deliveries with the L-134 engine, to have the original engine replaced with an F-134. With this engine swap, the gauge and sensor did not match, and the "gauge reads backwards" problem arose.

The original heat sensor for the L-134, Willys-Overland P/N 638699, is available, but will not fit into the threaded hole in the F-134 cylinder head; it's too big. The replacement temperature sensor available from several sources is advertised to properly operate 6-volt King-Seeley gauges; however it will not operate properly with the early "upside-down" gauges. Reversing the leads on the gauge (a commonly suggested fix) does not correct the problem.

This adapter is designed to operate with the following temperature sensors, also called temperature switches part number: 905926.

These are the sensors that make the old "upside-down gauges" read backwards.  I have tested another sensor, P/N 914847 that appears to be electrically the same sensor, but with a threaded brass adapter to fit a larger thread size in the engine.

Adapter, Front View

Adapter, Rear View

Adapter, Interior View

Specifications

Functional Description: The adapter is a voltage controlled pulse width modulator that varies the current through the temperature gauge in response to the engine coolant temperature.  At colder coolant temperatures, more current flows through the gauge, driving the needle to the left (100-degree) mark. As engine temperature rises, the current pulses decrease in width and the gauge heats less, moving upward on the gauge scale. The gauge is driven on an on-off mode as it was driven by the original "temperature plug".

Input Voltage: 6-volt Willys-Overland electrical system. Voltage at normal charge should be above 7.2 volts. No damage, but will not function properly if used with mechanical 12-volt to 6-volt voltage reducers.  

Overvoltage Protection: No damage to unit at inputs up to 16-volts for up to 15 minutes.

Reverse Polarity Protection: No damage if connected to reverse polarity supply.

Fits:
46-51 Truck
46-51 Station Wagon