Info needed: Water temperature sending unit

[Jacques Reed]

Originally Posted by Tony Smith

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 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.

Hi Tony,

I stand corrected on the use of the double contact sending unit pre-1949. I should look at more post war Ford passenger car engines and not Ford truck engines. I agree however it seems stupid to not fit them to the Military engines.

Reading the service bulletins and looking at the diagrams kindly posted by Lynn. the second dual terminal sending unit (temperature switch) is installed in series with the single terminal sending unit. It is factory preset to open at 195 degrees which results in infinite resistance- ie no current flow to temperature gauge and a resulting full deflection of the needle to "Hot" So it cannot produce a variable resistance, only produce an open or closed contact.

Service Bulletin states:
"It is merely a circuit breaker which opens the circuit at this pre-determined temperature so the dash unit reads hot. It does not control dash unit operation at temperatures below this point"

So in effect it is just an "idiot light" switch as mentioned in the HAMB thread. It will not indicate the actual water temperature in that cylinder bank. It only makes the dash unit's needle show Hot when that cylinder bank's temperature exceeds 195 degrees.

Still, I personally would rather have some indication of both cylinder banks water temperature than just that of one and none of the other.

Cheers,

Cheers,