Topic: Temp sender comparison Ford vs Aftermarket

[midlife]

OK, here's what I am thinking.  Unlike fuel sending units, the temp sending unit may well have resistances outside of the gauge requirements.  Why?  If it is cold, who cares what the resistance is if it is 30* below outside and you're just starting the car.  The gauge should register a temperature something a bit over any expected ambient, say 100 to 120* at the lowest end.  So, measuring 300 ohms at 70* (ambient) may be correct; what is needed is what temperature the gauge first moves off of the leftmost point. 

Similarly, the gauge may well read 5 ohms at 250*, but that is too high a reading to be of much use.  I would surmise that the gauge, when reading goes beyond its highest normal mark, should represent about 230 - 240* (e.g. 9-13 ohms). 

The same may well go for oil pressure sending units.  The lowest reading should correspond to something like 20 psi/70 ohms (my guess) and the high reading may be 90 psi/13 ohms. 

[RoyceP]

I only measured with a very accurate meter and reported the results. The Drake part is clearly unlike Ford parts in every imaginable way.

[rocket289k]

Hi Everyone,

This thread reminded me to post the results of my experience with reproduction Temperature Sending Units.  Royce, I feel your pain.  In general reproduction temperature sending unit OHMs readings are all over the place (especially the generic Napa or other auto parts store versions).  I finally gave up and was fortunate to find an original NIB FoMoCo C3AZ10884A part that worked perfectly and didn't cost me an arm and leg.  The reproductions in general just don't seem to produce the OHMs readings that the factory temperature gauge expects.  I've attached the result of 3 different sending units.  The Scott Drake repro in my case was "closest" to the original FoMoCo part but still produced a warmer gauge reading than it should have.

Symptoms - Car Engine running hot after replacing temperature sending unit (original died) with Napa procured part.  I assume the sending unit that died was a repro too (looked different than the FoMoCo part) but worked properly.


Approach (Engine 289 A Code)

1 - Used a digital infrared thermometer to measure the temperature of the engine at normal operating temperature (temps in and around 180F)
2 - Bench Test - Tested temperature sending units with a Digital OHM meter and hot water bath (heated to 180F).  Measure OHMs COLD (room temp) vs. in 180F Water bath
3 - Installed on Engine - Measure OHMs COLD and with Engine at Normal Operating Temp (produced same results as bench test)

With the FoMoCo temperature sending unit installed the Temp Gauge in the car reads points almost dead center at normal operating temperature (Red arrow).  The Scott Drake the gauge read on the right side of the M at normal operating temperature (Purple arrow).  The unknown brand (sourced from Napa) read between the M and P at normal operating temperature (Gold arrow).

See attached images for test results and Gauge Readings.

Regards,

Ron

[Brian Conway]

Results from a little experiment I did a while back myself.  OE sender w/bushing if that matters.

[Bob Gaines]

I try to nab every temp sender I come across out of intake manifolds for that reason. On closer inspection after I get them out and cleaned up turn out to be genuine Ford mostly. Times are change however.  The aftermarket ones I put in the circular file rather then risk the stress of having them give a wrong reading.