On Sep 5, 3:00 pm, "Mike Spera" wrote:
I am in a quest to troubleshoot an oil temp that has crept up a bit in the
last 100 hours or so. Checked all the baffling and"usual stuff". I was going
to check the accuracy of the gauge via testing.

2 things that I cannot find: the part number of the oil temp sending unit
and a supplier. This part does not appear either in the engine parts list or
the airplane parts list. Engine is a 150hp E-3D.

Any info would be appreciated.
Thanks,

Mike

Spiking oil temp can sometimes be blamed on poor engine and/or
alternator grounding. That little sender is a thermistor whose
resistance drops as it gets warm, allowing the electrical system to
draw more current out of the engine case, through the gauge and into
the bus.

Now, the alternator is generating electricity. It charges the battery
and powers the bus by "pulling" electrons from the bus and dumping
them into the crankcase to which it is bolted and into the firewall,
to which it should be grounded by a separate cable. If the cable
connections are bad, or if the crankcase-to-engine mount strap
connections are bad, or if the engine mount's interface with the
firewall is bad, those electrons look for other ways to get to the
airframe. They'll travel along control cables, wire shielding, and
yes, through the oil temp sender and through the gauge, having a
boosting effect and making the gauge read higher. You might get
alternator noise in your headset, too.

Cessna had a similar problem and now they recommend a separate, small
ground wire from the case near the sender to the gauge frame itself.
That keeps the potential as close to ground as possible and improves
accuracy. But if engine grounding is poor, hard starting will show up
and some of those little ground wires and engine control cables will
get hot.

I'd start by cleaning all the ground connections. Then see if the temp
is still too high.

Sometimes oil coolers get sludged up and internally coated with
varnish and crud, insulating the hot oil from the cooling airflow.

Dan