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Old 01-19-2020, 12:57 AM
Reilly Reilly is offline
Join Date: Oct 2008
Location: South Africa
Posts: 63
Default Light switches cause spike in oil temperature

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?
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Old 01-19-2020, 01:26 AM
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GeoffP GeoffP is offline
Join Date: Sep 2018
Location: NSW, Australia
Posts: 152
Default Voltage drop?

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.
RV-9, Tail Feathers done, Wings almost done.
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Old 01-19-2020, 06:25 AM
vic syracuse vic syracuse is offline
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,617

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 Syracuse

Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
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Old 01-19-2020, 08:17 AM
rocketman1988 rocketman1988 is offline
Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,177
Default ...and

This issue is detailed in The Aeroelectric Connection book...
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Old 01-19-2020, 08:25 AM
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bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 319

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.

Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Empennage Complete.
2018 RV-7 QB -- Built, Flying
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