Rotax 912 cht/coolant sensors?

[109JB]

I'm getting ready to put together my home-brew engine monitoring system and came to a realization. My 912UL is an older one that has cylinder head temperature sensors and as such do not actually contact any fluid. It appears there is no provision for a direct reading of coolant temperature on this engine. Granted I was looking at the engine in my dimly lit barn addition. So the question is on these older engine with the CHT in the bottom of the #2&3 cylinder heads, is there or should there be another sensor for reading the actual coolant temperature? If so where should it be/go?

[3 tracks]

I Welded a aluminum bung 1/8 npt into the spider tank, it worked great. Hottest spot in the coolant. The dry holes in the head work okay for the chts. I would install egts on every cylinder also.

[jrevens]

I Welded a aluminum bung 1/8 npt into the spider tank, it worked great. Hottest spot in the coolant. The dry holes in the head work okay for the chts. I would install egts on every cylinder also.

Seems like that would be the coolest spot - directly after the radiator and before it enters the engine. Am I wrong?

[jiott]

This subject has been discussed many times on the Rotax-Owner.com forum. The difference between the older dry hole cht readings and the newer coolant temp readings at the cylinder head are not enough to get excited about. The main conclusion I got from the discussions was to properly label your engine monitor readout as "CHT" or "Coolant T".

[109JB]

Seems like that would be the coolest spot - directly after the radiator and before it enters the engine. Am I wrong?

According to the maintenance manual, the coolant flows in this order water pump - cylinder heads - expansion tank - radiator - back to pump.


26209

That said, I may jut put a probe in a tee on the line back to the pump.

As far as EGT goes, I'll probably start without but being a home-brew project I can always add later.

[avidflyer]

I installed a thermo bob 1 thermostat to keep my coolant temps up mainly for winter heat. It seems to have done that fairly well. It would be real easy to drill and tap a 1/8" NPT hole in that housing to install a sensor. That housing is about 4" downstream of the spider tank, so it should be pretty accurate on reflecting engine coolant temp. The thermostat housing has a bypass line, so there is always coolant flow going through. JImChuk

[109JB]

This subject has been discussed many times on the Rotax-Owner.com forum. The difference between the older dry hole cht readings and the newer coolant temp readings at the cylinder head are not enough to get excited about. The main conclusion I got from the discussions was to properly label your engine monitor readout as "CHT" or "Coolant T".

Understood, but if it is easy to add I'll add it. For my project it's just a few lines of code. I just found in the manual where it says:

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So This is applicable to my serial number and it says to permanently monitor CHT AND coolant temps. So I guess I'll do it.

[109JB]

I installed a thermo bob 1 thermostat to keep my coolant temps up mainly for winter heat. It seems to have done that fairly well. It would be real easy to drill and tap a 1/8" NPT hole in that housing to install a sensor. That housing is about 4" downstream of the spider tank, so it should be pretty accurate on reflecting engine coolant temp. The thermostat housing has a bypass line, so there is always coolant flow going through. JImChuk

Great idea. I have this one https://www.amazon.com/Ice-Crusher-MaxStat-Thermostat-Radiator/dp/B082YGYS1B/ref=sr_1_13?dchild=1&keywords=utv+thermostat&qid=1606245488&sr=8-13 which also has a bypass. I'll just put a 1/8" NPT for a temp sensor there.

[jrevens]

According to the maintenance manual, the coolant flows in this order water pump - cylinder heads - expansion tank - radiator - back to pump....

Of course... thanks for clearing the cobwebs from my brain, John!