Dan,

When I said I checked the "usual stuff", I meant that I already did all the
things you suggested. Oil cooler and Vernatherm replaced with new units, all
connections checked, alternator running properly, gauge and sending unit
properly grounded, baffles sealing, etc.

I am looking for the part number of the sending unit and a source. If it is
cheap enough I may get one and swap it. Getting an immersion heater in a
vessel with the sending unit and a thermometer is a lot of stuff to juggle,
especiall once the heater starts heating up the water.. Done it before. For
a 10 buck sender, I would just replace it. However, if the thing is $50 then
I'll bite the bullet and do the test.

Thanks for the clues,
Mike


wrote in message
...
On Sep 5, 6:58 pm, wrote:
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

Should have pointed out one more possibility: The Vernatherm, which
controls the oil cooler bypass. As the oil warms up the vernatherm
pushes a valve into a port so that the oil has to go through the
cooler instead of bypassing it. If the Vernatherm is shot, the oil
will get hot.

If your engine has an oil screen, the vernatherm is the big nut on the
back of the screen housing right next to the temp pickup. If it has a
spin-on filter, it's in the bottom of the filter adapter, opposite the
temp sender which is on top.

Dan