Rotax CHT probes double duty.

[Esser]

So I am not using the two probes on the #2 and #3 cylinder since I am getting CHTs on all four cylinders via spark plug terminal. My question to you wise men, can I take those two probes and use them else where? I’m thinking of putting one in the rad for coolant temps which I think will work fine.

The other one I want to put in the intake manifold so I can monitor temps in there. I know this probe probably wasn’t designed for that in mind. These probes I think go up to 150C. Do they have a lower limit where they stop reading? My I take manifold shouldn’t go higher than 90C... or should I just go buy a proper manifold temp probe and stop being cheap?

If I do buy an off the shelf prob, I would probably get an automotive Bosch style one. They come with a two prong male plug. I’m assuming I can hook my one EIS wire to the other and the other to a ground and it will work just fine? It’s not proprietary Bosch stuff?

[PapuaPilot]

I don't see why they wouldn't work for an alternate purpose. Most likely any probe you get will be an alumel-chromel type.

They should not have a problem reading lower temperatures. In the winter I usually look at my CHTs and EGTs to get an idea of the engine temperature before I start it. I have seen them reading accurately down around 30F. I have 9 probes that I can compare (CHT, EGT and OAT).

I kind of like your idea, I can be a cheapskate too.

[jrevens]

With a “glass panel” I assume you can program for different types of sensors and different ranges.

I believe that those Rotax sensors are a variable resistance sender (RTD, thermistor, etc.). I’m not sure of the range, but they are surely designed for somewhere around a 12 to 24v max. circuit voltage.

The two metal alloy sensors like Phil mentioned are thermocouples. They produce a variable voltage depending on temperature. They are also mainly used for EGT measurement in aircraft.

[Esser]

Yeah these aren’t the thermocouple wires. Looks like the probes go up to 150C. The VDO part number show a “switch” value of 90C so I’m wondering if that means it doesn’t send below that?

I think if I make these probes work the biggest issue will be they don’t fit in an NPT boss since it’s a metric course thread pitch.