AC Champion Oil Temperature Sender/Gauge

[Gomer Pound]

Hi, I have read most of the threads on Oil temperature senders, but I did not find any mentioning AC brand sender/gauge combos, or maybe I did not realize they were AC senders. My senders have AC stamped on them. I assume I have AC gauges since the senders are AC. I purchased my plane recently knowing the right engine oil temperature read higher than the left, sometimes getting close to the red line, but not on the red line.The prior ownder said the right engine oil temp had read higher ever since he owned the plane, including after and engine overhaul he had done. I want to know if the right engine is in fact running hot or not. I tried to tackle this scientifically as others have done. 1967 Twin Comanche B model.
I first removed the right engine sender and put it in a stainless steel tall (but not wide) bowl filled with cooking oil. I used a Ivation digital meat thermometer.I took multiple measurements of the resistance values with my Fluke digital VOM. I noted inconsistent results which I believe is related to not getting a good ground even though I used a larger alligator clip. It was such a pain in the butt I did not test the left sender.
Today I used an ELENCO 1% resistance box which I found to be surprisingly accurate after testing the values with my Fluke. I tested both the right and left engine senders. My values are a bit different than I have seen in the forums, so I thought I would publish them. The red line Ohms seem to be similar.
First of all, the 60 degree value for both gauges is 300 Ohms, not 600+ ohms. The redline values for the gauges are around 20 Ohms.
RIGHT engine 300 ohms, 60 F (the needle in the middle of the white line) . 120 Ohms, slightly more than 60 F (not a full needle's width), 100 Ohms, mid between 60-240F. 90 Ohms, 1/2 needle width above mid 60-240 F. 80 Ohms, full needle below 200F. 60 Ohms, 220F. 50 Ohms, just below 260. 40 Ohms 260F. 30 Ohms, 260F+ 1/2 needle width. 20 Ohms pegged full.
LEFT engine. 300 Ohms, 60F (the needle in the middle of the white line), 80 Ohms, mid between 60-240F, 66 Ohms, 200F, 46 Ohms, 260F, 30 Ohms, one needle width more than 260.
So, the left oil temp gauge actually indicates slightly higher than the right gauge at higher temperatures.
I am replacing the external power plug and the Battery & AUX relays, as well as installing one of the new Battery Minder approved harnesses. As soon as I get things buttoned back up I will test fly and see if swapping the senders changes the relative temperature values. If the values change so the left engine is higher, then it is most likely the sender.
I was going to fly, get the engines warmed up, then land and measure the oil temps using the digital meat thermometer down the dipstick tube, but I decided this would not tell me if the higher temps I might see in flight were "real" since the engine oil would cool down.
The oil coolers were overhauled when the engine was done 1250 hrs ago.
I made a rough graph of the the values, but the gauges have such imprecise markings, it is difficult to assign an exact value for the temperatures unless you are at 60 degrees or 260 degrees.
IF the sender is bad, I am not looking forward to pulling both of the Oil Temp gauges and converting to the Rochester gauges.
Any input on the AC gauges is appreciated.

[Gomer Pound]

I flew the plane this morning on an hour cross country after swapping the Right and LEFT oil temperature senders. Now the LEFT oil temp reads higher than "normal." The RIGHT engine oil temp was centered @ 200 degrees. The LEFT was a needle's width to the right of 200 degrees, so the oil temp sender was the cause of the high RIGHT engine oil tempss not the oil temp gauge. Now to see if I can possibly find a good AC oil temp sender.
Gomer