Light switches cause spike in oil temperature

[Reilly]

Hi
I have a RV9 with a O320

It has 795 hours and now if I turn any of the landing light, strobe or nav lights on it causes an immediate spike in my oil temperature reading.

Any idea on where I should start looking?

[GeoffP]

I'm no expert by any means, but if the sensor relies on voltage then what you may be seeing is the drop in voltage from switching on something else. I'd probably look for a bad connection (either power or earth) to your oil temp sender.

[vic syracuse]

You have a bad ground. The oil temp sensor is nothing but a resistor that changes according to temperature. We are basically measuring the voltage across the resistor to ground.

First, check your engine ground. It is the most likely source. If not that, check the ground(s) to your instrument panel.

Vic

[rocketman1988]

This issue is detailed in The Aeroelectric Connection book...

[bjdecker]

Concur with others -- this is a grounding (current return path) issue. Either the grounding to the airframe at the lights -OR- the gauges, etc.

I had a '80 Mooney 231 that would do the same thing every time I keyed the mic - turned out to be a bad ground on the analog instrument cluster.

Cheers!