Coolant System

You do not have a problem!

The operator's manual allows for Oil Temps up to 130°C (266°F).
And Coolant Temps up to 120°C (248°F) for 50/50% Ethylene Glycol (EG) Coolant.
The Limits are Not where the Engine Blows up, They are where you need to start taking action.

What Heads do you have?
The Older Heads had the Temp Sensors on the BOTTOM and measured CHT. (Dry)
The Newer Heads have the Temp Sensors on the TOP and Measure Coolant Temp. (Wet)

It is recommended (Not Required) that you run the OIL over 100°C periodically to boil off the combustion water.

The Head Temp is limited to 120°C because 50/50% EG Coolant boils just above 125°C (~260°F) under pressure.
It is not because the engine can't handle the heat, it is because the Coolant can't.

The Head itself is Red Lined at 150°C (302°F)
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If your Radiator is heating up to 70°C and both ends are the same; the Coolant is Definitely circulating.

If you do not already have this ...
If you use clear plastic tubing for the hose from the Expansion Tank to the Overflow Bottle, This hose will indicate if your coolant system is working properly as it should be completely full of coolant at ALL times.  
If you see more than a small bubble of Air in this hose, something is wrong.
This tubing does NOT get more than bath water Hot under normal operation.
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HELP!
Does anyone have a Pre-2015 ULS Operators Manual in their Archives?
What was the upper limit on the CHT before they changed the Heads?
Could you send me a copy?
Bill

Hi Bill,

Thank you for taking the time to deliver such a comprehensive response. My unswears/observations are as follows;

Oil & Coolant temps - I understand the operational limits, however I am trying for a sub 100C for ground ops in the current 15-16C ambient (spring) temperatures in anticipator of higher temps when summer ambient's will be the norm.

Coolant Sensor Location - this is the newer head with sensors on top measuring coolant.

Oil temp recommendations - Yes I have always looked to have at least one short period of over 100C during each sortie. In my past experience, this usually occurs on climb out.

Radiator tank temps - Your comment is interesting. I would have expected a significant difference between IN (Hot) & OUT (Cool). Please expand.

Expansion tank hose- No I don't have a transparent  hose - will look into fitting one. 

Don't think I can help with the pre 2015 Operators Manual - Sorry!

ADDITIONAL OBSERVATION

I have always understood/accepted that the main engine cooling influence is the coolant radiator (followed by oil & cylinder barrel fins).

In a recent test of my system, with no cowling, I was unable to get engine (oil/coolant) temperatures up to optimum (or any where near it).

Just to get a "handle" on what was having the most influence on coolant temperatures (oil/ barrel fins/coolant (radiator) I completely blocked the IN side of the radiator air flow - virtually no change to temperatures.

What might your interpretation of this experience be?

Sean Asked,

Radiator tank temps - Your comment is interesting.  I would have expected a significant difference between IN (Hot) & OUT (Cool). Please expand.

The Circulation of the coolant is fast enough that there is almost no significant temperature drop. 
The coolant pump moves 10s of liters per minute and the system might hold less than 4.
So the full coolant volume might do a round trip in well under 10 seconds.

I would have expected the Radiator to be very close to the head temp.
Do you have a Coolant Thermostat in the system where some coolant is bypassing the Radiator?
Or possibly you are measuring the surface temps of the radiator header tanks (Plastic?) and not the actual coolant within the tanks.
- - -

By Ground-Ops, I assume you mean taxiing to and from the Runway and not static Ground Running.
To paraphrase Roger, Get It Moving!!!  You will see a significant difference.
The engine was meant to fly, not blow leaves!

"The Circulation of the coolant is fast enough that there is almost no significant temperature drop."

Sorry Bill - this does not make sense to me - if there is no temperature drop across the radiator, there can not be any cooling effect ergo the radiator is not doing the job that I expected of it.

"I would have expected the Radiator to be very close to the head temp."

So would I - so why would the CHT be around 115C & the radiator be 70C?

"Or possibly you are measuring the surface temps of the radiator header tanks (Plastic?)"

Yes I taped the thermocouples (one each side) to the  radiator tanks (fairly sure they are metal but will check again). Used an insulated tape to contain the temp around the thermocouple & reduce any effect of air movement.

"By Ground-Ops...", 

At the moment the fuselage (wings/tail yet to be installed) is just secured (static ie not moving) cowling facing into wind. Yes fully expect any forward movement (taxying) to improve cooling BUT as I have said, day ambient is about 15C at this time of year (winter/spring) and will rise to mid 40C's mid summer. If the cooling system can not keep temps below 100C x 15min run time, at this time of year, how quickly will temps rise when ambient is say 30C?