Info needed: Water temperature sending unit

[Harlé Sylvain]

Hello
Does someone know a modern replacement for the flathead ford temperature sending unit,( the original one is a bit expensive, mostly after shipping and taxes to france).Also I have only one side hole on the cylinder head on my flathead.

I use a 6v dash with a 12v reducer. I heard about ford truck units of the 70th?

Cheers

[Peter Duggan]

Harle,

If this is what you are looking for, Macs Auto Parts has them.

Peter

[Jacques Reed]

Originally Posted by Harlé Sylvain

Hello
Does someone know a modern replacement for the flathead ford temperature sending unit,( the original one is a bit expensive, mostly after shipping and taxes to france).Also I have only one side hole on the cylinder head on my flathead.

I use a 6v dash with a 12v reducer. I heard about ford truck units of the 70th?

Cheers

Hello Harle,

Your question is interesting for all us owners of old Ford Flathead V8 powered vehicles.
We have the same problem in Australia- cheap parts in the US cost a small fortune here with shipping and exchange rates. As an example: I just bought 8 gun screws from the US. Cost was only $3.50 but it was $11.40 for postage.

It got me interested and I found this thread on the HAMB which might be of interest as others have tried to find a cheaper or more readily available temperature sending unit for the old Ford engines.

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

Upon reading it I am of the belief that it may cost a bit more, but one from a reputable supplier of old Ford parts is the best option. Even better would be a NOS unit if one can be located.

They are very robust units and it is worth testing it in hot water before condemning it to the scrap bin and searching for a new one. Just because it is old and may be rough looking it might still be functional.

Of interest: Pre 1949 engines had only one sending unit. Later 8BA engines used two. The second one was just an overheat bi-metallic switch that pegged the temperature gauge fully to hot when the contacts closed. It is distinguishable by two terminals on the sender. It is just an "idiot light" arrangement for the bank of cylinders that didn't have a resistance type sending unit to show the temperature.

Hope this is of some help.

Cheers,

[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.

[Lynn Eades]

The talked of diagrams. All mixed up and random. You work it out. The last service bulletin supports Tony's comments (from 1939)

[Lynn Eades]

Some more.

[Lynn Eades]

And the last two pages.

[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,

[Lynn Eades]

I guess Jacques, we are banking on any cooling system fault to be common to both banks, which in the majority of cases of "normal use faults" would be how it happens...

[Tony Smith]

Originally Posted by Harlé Sylvain

Hello
Does someone know a modern replacement for the flathead ford temperature sending unit?

I use a 6v dash with a 12v reducer. I heard about ford truck units of the 70's?

Cheers

Harlé, I hope that the above discussion has not been too technical in English.

You will have noted the operation of the gauge. In the 6v system, the gauge at the dash shows "Hot" with no or low voltages and "cold" with full voltage. The sender on the engine has low resistance at cold temperatures, and increases resistance as the temperature climbs.

In 1956, Ford cars and Trucks changed to 12V electrical systems. The 12v gauge now worked in the opposite way. It showed "cold" at no or low voltage, and as the voltage increased moved to "Hot". The sender on the engine had a high resistance at cold temperatures, and the resistance lowered as the temperature increased.

Using a Ford 12v sender from post -'56 will only work with the corresponding gauge. The may look the same and have the same 3/8ths thread, but they will not correctly operate the 6v gauge, even with a voltage regulator.

EDIT The above applies to the temperature gauge system in use with US/Canadian/English/Australian Ford vehicles. I cannot confirm what temperature monitoring system was used on the French Flathead (SIMCA) or Matford Trucks, which I recall from an earlier thread was the source of your engine. In any respects, it is the 1940's Ford 6v gauge on the dash which you want to function correctly.

[Jacques Reed]

Originally Posted by Lynn Eades

I guess Jacques, we are banking on any cooling system fault to be common to both banks, which in the majority of cases of "normal use faults" would be how it happens...

Hi Lynn,

Totally agree with you. About the only scenario I could see is a severe leak in the bank with the "switch" either from a severely leaking hose or a blown head gasket but the temp would rise rapidly anyway in the other bank due to overall coolant loss. A torn fan belt would also result in a rapid rise in both banks so it probably isn't as essential as I originally thought. Obviously Ford thought so too for 12 or more years.

Thanks for posting those service bulletins. Myself, and I am sure many others, now know a lot more about those vital engine parts than we did a few hours ago.

Cheers,

[Harlé Sylvain]

Hello
And thank you all for all this explications, and especialy at Tony for is short explication ,it's true it's not alway easy to understand everythink.

I will try to find a post 56 gauge, my simca engine was a 24v and I cant keep nothing, an my cluster is not very nice , I think it will be the best.

Cheers
Sylvain