|This is another variety of the Boyce motometer on a radiator cap plus an additional accessory.
The aluminum winged cap is some 9" from wing tip to wing tip and this model has a door that opens to fill the radiator. The door unlatches by using the knurled brass knob, it then swings down allowing the engine coolant to be added. The cap is called the Protect-O-Cap, and was manufactured by the Up-To-Date Machine Works, of Chicago, Illinois.
The Boyce motometer is 3-1/4" in diameter and nickel plated. On the front of the motometer is a device called the Glo-Light. This could be lit from a switch on the dash allowing the driver to view the thermometer condition at night. Viewing the unit from the front shows a white lens in the centre. There is also a red window lens on the left - passenger side, and a green window lens on the right - driver side. This is the United States configuration.
Another variety of this attachment is shown in the bottom two photographs. This variety has a blue centre lens with red and green jewels on each side. The attachment is the same size as the one shown on the cap, and was produced by the Never-Out Company of Philadelphia, PA.