I have wondered if the same person at Dynon always answers the questions and post on the forum.
In my first post in this thread I said "Today I measured the resistance across the sensor, then to the accessory case, then to the grounding strap on the engine and finally to the grounding tabs on the firewall. At each location I got 365 ohms."
Dynon responded with..."Where exactly are you measuring Ratman? If the sensor is actually 89F degrees, it should be reading 537 ohms. In contrast, 365 ohms would get you about 107F on the display."
So.... It's the sensor, right? No, let's keep looking.
Dynon suggest..."One thing you can do to rule out the sender is install a fixed resistor in place of it. A 47 ohm resistor should read about 219 degF. If you unhook the wire from the sender, put a 47 ohm resistor there, and ground it to a good ground, you can then play with things and see if the temp changes. If nothing changes the temp (loads in the plane, alternator, vibration, etc), then the sender might be bad. No idea how it could read right at one temp and not the other, but I guess anything is possible."
So that's what I did..."A 47 ohm resistor got me 223 degrees. I then tried just about every combinations of lights and radios and alternator I could come up with. Many of the combinations that I wouldn't even use in flight. and the 233 remained stable."
So... It's the sensor, right?
Dynon---"The 219 vs 223 is probably expected given the variance in resistors. Most resistors are 5% tolerance. The important thing here is that it didn't change at all as you tried things.
Just to check, the resistor was hooked to the same place that the sender was? It wasn't grounded to a different place?"
No it wasn't grounded to a different place, it was grounded to the accessory case right where the sensor is installed. Also I used the newly installed ground strap that Phantom suggested. Both test yeilded the same results.
Dynon---"If that's true, then it looks like your readings are right and the real issue is actually high oil temps. The senders are just a material that changes resistance over temperature, so it's not really possible for them to be right at one temp and then not another other."
HUH?!?