Erratic temperature readings on XTreme

[oconnom]

My XTreme has worked perfectly for several years and then suddenly last year it started playing up. 10-15 mins after takeoff my oil temp would start fluctuating up and down, followed quickly by the CHTs and EGTs. This condition would continue f until shut down.
It was suggested that it could be voltage spikes on the bus so I fitted and isolate switch between alternator out put and regulator (Jabiru 2200 engine). When the temp issue started on next flight, I isolated the alternator and everything returned to normal. I fitted a new regulator and on next flight issue had gone. The unfortunately after 3 hrs flying problem returned (45 minutes into last flight ).
Any suggestions what it could be ?
Mick

[rainier]

That very much sounds like a grounding issue related to your RDAC. The time variation you experience are likely directly related to your battery charging current which in this case mask the issue at first - but as the current gets less the RDAC's ground potential moves further from that of the engine block.
Make sure you have a single, unshared ground wire from the RDAC to the engine block and there is no corrosion (not even a little bit !!!) at the connections. Make sure the RDAC does not have any accidental secondary grounds. Usually you use the power supply ground of the RDAC as ground so that goes to the engine block direct. If your RDAC has any additional ground terminals (like the RDAC XF for example) - these are intended to serve as grounds for ISOLATED senders - do not connect these to other random ground points in your aircraft like airframe etc.

[oconnom]

Thank you for that comprehensive reply, I will thoroughly check the earths as suggested.
Mick

[oconnom]

Just a couple of thoughts:
Why would a ground issue just arise after years of no problems ?
Could it be a bad battery ?
Why did a new regulator solve issue for 3 hrs ?
Mick

[bvolcko]

Corrosion?

[bvolcko]

Good to see you back here Rainier!