Rotax 912ULS - Second oil temperature sensor

by Roger Spall in 912 / 914 Technical Questions 6 years ago

Just purchased an aircraft with an EFIS connected to the 912ULS oil temperature sensor.

Everything works fine, and just installed a new digital Tach with non volatile hobbs / tachometer hours. This new digital instrument also has input for temperature (oil). Because temperature is a resistive measure, I cannot parallel two gauges on the same input source.

Is there a (simple) way to add a second oil temperature sensor to a Rotax 912ULS ?

Thanks,

Roger

Re: Rotax 912ULS - Second oil temperature sensor

by Roger Lee » 6 years ago

Roger Lee

126 5.14k 4.62k

Hi Roger,
There is no real reason to have two oil temps. Rotax and owners have been using just one for 29 years on the 912 series. If you like your new instrument better than your original one just swap them for the reading.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Rotax 912ULS - Second oil temperature sensor

by Roger Spall » 6 years ago

Roger Spall

4 10 0

Roger,

I hear you... My EFIS keeps losing the hobbs / tach hours (doesn't have non volatile memory), so I purchased a separate digital tach with non volatile tach / hobbs - doesn't lose my hobbs / tach hour totals.

Anyway, for 60 bucks more I got Manifold Pressure and oil temperature input and I thought I may as well use them (nice backup). I was hoping to not have to choose between EFIS and new gauge for temperature, but it looks like I may have to :-) My EFIS has CHT, EGT, and oil temp all nicely displayed next to each other so I will probably keep the temperature going to the EFIS and turn the function off on my new gauge so I don't get constant warnings.

Thank you.

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Re: Rotax 912ULS - Second oil temperature sensor

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.97k

I am with you! I run a small Mechanical Hobbs activated by an oil pressure switch.
The EFIS can lose its mind at any time. The mechanical Hobbs just keeps ticking.

You actually have multiple options depending on how creative you want to get.
The Oil Temp on 912ULS measures the temperature of the oil as it enters the engine after coming from the cooler.
What you are measuring is the Oil at its Coldest point.

Option 1.
The casting for the Oil pump is used to manufacture Oil Pumps for a number of different engines.
They are almost all the same except for what holes are machined into them.
Notice that on the Front of the Oil Pump Housing, next to the Oil Pressure Sender Port, there is a blank port that goes nowhere and is not threaded.
This port is used to supply oil to the TurboCharger on a 914 engine.
If you were to drill and tap this port, you could use it to mount your second sensor.
It will not be in flowing oil so you will not get an identical reading, but it will be close.

Option 2.
There are multiple Oil return line ports on the bottom of the crankcase that the engine installer can select from depending on whether the engine is a Pusher or a Tractor.
If your Oil return line is connected to the Aft port, the Forward Port has a plug in it.
You could adapt your sensor to mount into this unused Oil return Port.
This location will report slightly higher oil temperatures than at the Oil pump as it sees the Oil leaving the engine heading for the Oil tank and Cooler.

OR...
You can just turn the function OFF.
It all depends on how much effort you want to make.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Thank you said by: Roger Spall

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Rotax 912ULS - Second oil temperature sensor

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