Right side coolant getting too hot

Hi Kevin,

I think you are on the correct track with your "trouble shooting".

Make sure the thermocouple connections are all clean (no surface corrosion) nice & tight/secure - may be use a smear of electrolytic grease between contact surfaces.

The thermocouples/temperature sensors used in most light aircraft are not precision instruments ie some variation is common.  My two EGT's started to give slightly diffrent readings a few hours into test flying. Investigation came up with no engine anomalies - I just live with it for the moment. 

Consistency is more  important than small variations, so record the readings and keep an eye out for for changes.

You can test  the probes in the steam just above the surface of boiling water (100C), multi meter or use a candle:

(from Google)

"Good Thermocouple:

A properly functioning thermocouple will generate a voltage that increases as the temperature increases.

The standard Rotax coolant temperature sensors (CHT sensors on old 912/914 engines) are not thermocouples - they are NTC thermistors. As their temperature increases, the resistance will decrease non-linearly. They should read approximately 60 ohms at 100ºC. (212ºF) You can find the calibration curve in the installation manual.

Still not sure how there could be a 33ºC/60ºF difference between the left and right coolant temp sensors. I suppose it could be related to the left sensor being on cylinder 2 (front cylinder in tractor aircraft) and the right sensor being on cylinder 3? (rear cylinder) I wouldn't know what's a normal difference - my aircraft (with older design heads) only has one CHT sensor on cylinder 3.

There are 2 sensors.  One for cylinder 2 and one for cylinder 3.  You should connect to the hottest one, the cylinder that runs in the rear in relation to the air flow.  For a tractor installation that would be number 3, for a pusher number 2.  It is a liquid cooled set of heads so they will never be exactly the same.  Airflow will play a large part in this if you are trying to read both it will just get you worried.  If the hot side is in the specs you are golden.  it is indeed a NTC thermistor and not a thermocouple as Tim pointed out.  The old version, CHT reading, enter from the lower part of the head casting and read material temperature.  The newer heads enter from the top of the head but use the same sensor, they read into the coolant jacket so are actually coolant temperature sensors.  The reading are not the same and you can see this in service bulletin releases what value each reads. 

The sensor for both the old CHT reading and the new coolant temp reading are exactly the same part number, just different locations and measuring slightly different things in the head. 

Cheers

My apologies -

I got fixated on the "...right coolant was up to 220, while the left was 160. " with the wholly incorrect interpretation, that Kevin's aircraft had two coolant radiators, left & right.😈