Coolant Temperature Measuring/ 912

Hi Sean,

Is yours a -01 engine?

Cheers.

Hi Des,

Mine is a Max 120C head coolant temperature but what I am intersted in is the reference to "Coolant temperature: (coolant exit temperature) Max. 120 °C "

In what location is the "coolant exit temperature" AND what is operationally achieved by being able to monitor this in addition to CHT (coolant) ? 

If your engine has the "CHT" sensors iserted into the top of the heads, you have an "engine S/N with Suffix -01" (as Rotax puts it) and the sensors are actually measuring coolant temperatures, not cylinder head temperatures. In this case, there is no point in installing another coolant temperature sensor, as it should always read lower than the coolant temperature sensors in the heads.

Engines built before about March 2013 have the temperature sensors in the bottom of the heads. These engines are what Rotax charmingly refers to as having "engine S/N without Suffix -01" and the sensors are actually measuring the temperatures of the head itself - i.e. they are conventional CHT sensors. I believe the coolant temp sensor referenced in the Operator's Manual is often installed in the coolant collector tank, although it can be installed anywhwere between the collector tank and the radiator. (Another option is to restrict the CHT redline so that the coolant temp cannot rise above 120°C.)

Around 2004, Rotax became aware of problems with the coolant boiling inside the heads under some circumstances with CHT's below redline temps. This prompted the initial issue of SB-912-043 (and the associated Austrian AD A-2004-004 / Australian AD/ROTAX/21), which originally required the use of waterless coolant only. Later revisions increased the coolant pressure cap from 0.9 bar to 1.2 bar and permitted the use of conventional coolant provided the coolant temperature remained below 120°C.

Since coolant temperature was more critical than cylinder head temp, in 2013 Rotax changed the head design so that the temperature sensor was directly immersed in the coolant, thus measuring coolant temperature instead of cylinder head temperature. This was initally communicated as a routine change in SI-912-020 ("Running Modifications on ROTAX Engine Type 912/914 (Series)"), however EASA's eventual position was that this was actually a large enough change that the engine's model number should be changed. As a result, Rotax SB-912-066 / EASA AD 2015-0240 was issued requiring that engines with the new heads installed have their model number changed by adding -01 to the end.

Further reading:

• Rotax 912 Installation Manual, Chapter 75-00-00

• Rotax SB-912-043
• Austrian AD A-2004-004 (superseded by EASA AD 2007-0155)
• Australian AD/ROTAX/21
• EASA AD 2007-0155

• EASA SIB 2014-34
• Rotax SB-912-066
• EASA AD 2015-0240

Sean Griffin wrote:

Hi Des,

Mine is a Max 120C head coolant temperature but what I am intersted in is the reference to "Coolant temperature: (coolant exit temperature) Max. 120 °C "

In what location is the "coolant exit temperature" AND what is operationally achieved by being able to monitor this in addition to CHT (coolant) ? 

Hi again,

I think I see where you’re coming from, attached is a quote from the installation manual.

My 2 bob’s worth in answer to your original question? If you are already monitoring coolant temperature in the cylinder head, you would gain nothing by additionally monitoring essentially the same parameter, with the same limit temperature, just a few inches further down the line AND potentially have a new place for a leak or 2 to start annoying you.

Cheers again.

Hi Sean,

Some owners have added another probe that is directly into the coolant, but I personally don't think it's a big benefit.The ones I have seen in place are between the expansion tank and the radiator. This is the hot fluid before it cools. Here you'll see the max coolant temp which is the important one, not the cooled coolant.