Temp sending unit match to work with oem gauge

[RD-72]

Technical assistance required...”for bench testing”
i am running a stock oem temp gauge and am trying to see what it takes to get it to talk with a non stock sending unit.

Situation:
My car was stock with the idiot light configuration for temp, oil, etc
I added in the stock tri gauge cluster in the center stack...leaving the stock idiot light setup intact (so I am running parallel systems)
I only have one spot on my 302 engine block for a sending unit, so I bought an Autometer in line 5/8” heater hose fitting.
The Autometer adapter accepts a 3/8” temp sending unit fitting (that limits the number of temp sending units that will fit).

I found a bought a Stewart Warner 280ED-F sending unit that fits the Autometer fitting
I bench tested the resistance of the sending unit (set at the 2,000 ohm setting) with the following approx. results:
ice water: 1,368 ohms
room temperature: 740 ohms
boiling water: 196 ohms
I also bought an Autometer sending unit that fits, but I haven’t bench tested the resistance as of yet.

From other information posted on this site, i understand that the stock gauge has a boiling water (hot) reading at around 100 ohms.

Questions:
Am I out to lunch, thinking that there is a way to get approx reading on the stock gauge? so that the sending unit and gauge talk to each other...i am looking to have normal operating temp in the middle of the gauge’s range (keeping in mind that the gauges do no have temp markings on them)
it seems to me that I should be able to do something to get them to talk (I’m no electrical whiz, but is there a resister or other gizmo that I can add inline to adjust the resistance?
Am I overthinking this? And just hook it up and see?


any thoughts/assistance would be much appreciated

thx all

 

[Don C]

The stock unit has a resistance swing of 10 (hot) to 73 (cold) ohms, so you'll never get it too work. Get one of these:
https://www.speedwaymotors.com/Clas...ders,37690.html?sku=27522-FORD&utm_matchtype={match_type}&msclkid=dc59dbd2b6ca16f25cdcb970119f9b0e&utm_source=bing&utm_medium=cpc&utm_campaign=SMI%20-%20Shopping%20(CSE)%20(Bing)&utm_term=4577404347346283&utm_content=All%20Products%20(Feb28_2020)

 

[basstrix]

I think Don already answered your question, but that sender won't work with OEM gauge. The resistance is too high.

Last weekend I checked the calibration of my temp gauge using a cheap variable resistor box off of amazon ($16). The pics below are the results. According to Rocketman's Gauges 101 post, the following is what the gauge is designed for:
Zero end of scale: 70ohms
Mid point: 26ohms
Full range of scale: 12ohms

My gauge needs 23 ohms to run mid-range.

I was messing with a thermocouple to correlate coolant temp with sending unit resistance, but I wasn't convinced with my numbers. I'm going to come up with a better measurement location.

Edit: Fixed the resistance vs which end of scale.

 

[Hemikiller]

The Autometer fitting accepts 1/8" NPT fittings. The factory sender is 3/8" NPT.

https://www.autometer.com/5-8-heater-hose-adapter.html
I would ditch the Autometer parts and get a Four Seasons adapter with the 3/8" NPT fitting for a factory temp gauge sender. Be sure to add a ground wire to the setup.

https://www.summitracing.com/parts/fss-84540

 

[RD-72]

I like that idea...looks like I will ordering the summit racing adapter...that should work out nicely
thx