912 ULS CHT, or CT?

Hu John,

Those are the most recent heads with the CHT probe inserted into the coolant on top. The older style was just into the metal portion and on the bottom of the head. Make sure the spade connector on top has a firm connection and not floppy lose.  Make sure there is no air pocket under the probe.

Is this a new occurrence or has it always been this way? What is the temp on your instrument? Is your oil temp up too?

Hi John,

were the crazy warnings high temp or low temp warnings? The probes are NTC-types which means they provide lower resistance values to your instrument when temps are going up. Trouble is that high resistance (when engine temp is low) provide high resistance values - such as a bad connection of the spade connector (when floppy, or a loose cable and what have you).

The probes themselves are not known to fail often (as far as I know), spade connectors are. Thus, if your readings were good for a long time and now went crazy you best follow Roger’s hint and check connection and cable.

High oil temps may lead to other conclusions for sure.

Hi John,

Further to Rogers advice regarding a good electrical connection to the temperature sensor;

Hard to see what sort of connector>sensor is shown in your photo, looks to be a standard female spade type. I have found that the spring type shown below is the best for this application. The spring gives posative connection even in high vibration/wind blast situations and remains connected until you depress the spring for removal. You should be able to get them through your local automotive store.

Hello Lads,

Thanks all for your reply.  

@ROGER - My oil temps are always fine, and never give a warning.  The probe displayed on the right runs away at times when on descent.  I can be coming down from say 6000ft the CHT probe displayed on the right side will run high, up into the yellow, but often into the red.  If I level out and increase the throttle, it would instantly go back down to normal range.  I have had similar with the EGTs.  They spike on descent, and then settle the instant I apply throttle.

Given that the temps of fluid can't be that dynamic, I have been putting down to earth ,or wiring etc.  I have never been able to nail it down.

I have swapped the probe, only to have the same issue on the same side - it did not follow the probe.

Bristell have set the range as per the following image, where, if I am reading it right, is not correct?  Am I right - Rotax say red zone should start at 120?

The 120C (248F) coolant temp is set more for the 50/50 coolant. If allowed to go to the 266F point it's  close to a coolant boil over.

Since the reading changes so quickly I'm leaning on a wire or connection issue. Have you checked in the instrument panel  where that wire goes?