Info needed: Water temperature sending unit

[Tony Smith]

Originally Posted by Jacques Reed

Hello Harle,

I found this thread on the HAMB ....

https://www.jalopyjournal.com/forum/...gauges.925581/

Of interest: Pre 1949 engines had only one sending unit.

Hope this is of some help.

Cheers,

Jacques, you will of course have noted that the thread you have linked shows a photo of the 1940 dual terminal sender (01A-10990) for use with TWO sending units in 1940 cars! The 2-sender system provides a marginally better indication of engine temps and was only available in Ford and Mercury cars, but not the trucks.

The cooling system of the Ford V8 is basically 2 4-cyl engines side by side. The coolant in the left bank of the Ford V8 does not mix with the coolant in the right bank until they both end up in the radiator. Putting just one temp sender in one bank completely ignores whats happening in the other half of the engine. It is possible to have very high temps, a failed water pump, or even a leaking head gasket on the un-monitored bank, and the temp gauge showing normal temp range on the other bank.

The 2-sender arrangement shows the highest temp of either of the two banks of the engine on the gauge . The dual terminal sender earths to the engine and its resistance is dependent on both the coolant in that bank and the voltage coming from the other sender. If the bank that contains the dual terminal sender is hotter than the other bank, it increases the resistance to show a lower voltage at the gauge, resulting in a "Hotter" indication. If cooler, it shows no resistance and reads the voltage from the single sender.

I have the Service Bulletin that explains the electrical circuit, and it was certainly in use in 1940. It's a mystery to me why it wasn't also used in commercial trucks, as they would be more likely to be worked hard and overheat, or specified for military engines, where presumably the marginal cost would be offset by a more reliable engine.