Utter Nonsense is it ?
Most glider tugs are flown by pilots who understand the task and the correct way to fly the aircraft, this was not always the case, a long time back ( forty years or so ) the British Gliding Association did a lot of work to define the best practices and techniques for the glider towing task. The after publication of the results of this work the mortality rate of engines and particularly cylinders dropped dramatically and now remains remarkably low considering opportunity for thermal shock during this task.
As most of the smaller Robin aircraft are flown by student or low time pilots it is unlikely that they have yet acquired the skills of the glider tug pilot in managing the issues of thermal shock.
Touring Robin’s. if you go touring in a Robin then you operate at near the MTOW on most sectors and also know that for best cruise performance you are going to plan the flight as close to 8000 ft as you can as this is the best altitude for the fast cruise , if the OAT is at about ISA+15 or above the Limitations of cooling system of the Robin will become apparent as at about 4-5000 feet you will find the oil temperature heading for the red line. This limits the climb as it is necessary stop the climb and to take up the cruise to allow the oil to cool enough to take another 2000 ft bite at the climb before repeating the process. Surprisingly CHT is not usually a problem as the best rate of climb is at 92kts with the touring propellor but with the glider towing propellor the best climb speed is 70kts, this reduction in cooling airflow makes CHT the most likely limiting factor for the glider tug as it is unusual to tow a glider much past 2500ft and the oil does not usually get hot enough in during the glider tow to be the limiting factor.
The Robin has to get its performance from some place with a very clever aerodynamics and the elimination of drag being the key reasons for the performance but the price is that idiot proof cooling Has been sacrificed to provide this performance. Management of the engine cooling issues are not insurmountable but the aircraft is not idiot proof.
Arne wrote:
At low temperatures, the thermostat will close the flow to the radiator and more to the bypass, so the engine stays warm and cosy.
Rotax 912 does not normally come with thermostats. Thermostats are aftermarket pieces. Good for the temperature in the engine, but it’s also an additional failure point. The 912 is not a liquid cooled engine like a normal car engine. Only the cylinder heads are liquid cooled.
Thanks for the answer A and C. I’ m not alone to have a hard time make robins climb 
Let’s take aside for a minute whether the aero club is right or wrong.
Let’s also take aside the unlikely effect of terminal damage by 1or 10 ovetheated climbs.
However I’d like to focus on why ‘this is utter nonsense’ and similar comments are necessary. Owners of several years experience, and other knowledgeable on type Pilots have added comments that a closely cowled ‘fantastic in group’ aircraft can suffer quite significantly, if not handled with care in high ambient temperatures.
Are you saying it’s not possible to run the CHT or OIL into the red? That the idea of doing so and being an issue is nonsense? That there is no chance to ‘Certify’ such an appalling design?
Try any high performance piston aircraft and find similar issues.
Jujupilote, the 1st time you get to try a DR400/180 with newish engine and only 2 people you will have a smile on yoir face. She will climb like a homesick angel. ;-)
Yes it climbs very well, but the oil temp and CHT (we have a single gauge) climb just as fast 
Without a CHT gauge, I can see all sorts of “operating limitations” going around, because everybody is working blind.
Peter
If you buy a basic Robin the instrument and radio fit is just about good enough to Fly around the circuit at Dijon. So the buyer will spec the aircraft for their own operational requirements and it is almost unthinkable that if buying a glider tug you would not make sure a CHT indicator was fitted, an EGT gauge is almost useless for the glider towing task as the aircraft is inevitably run full rich most of the time.
Those of us who use the aircraft for touring need both as EGT is critical for cruise engine setting and CHT is a limitation if you are trying to hit the best angle of climb 70 kts rather than best rate at 92kts
It says a lot for the Robin DR400 airframe that it can perform such diverse tasks very well but it does require good piloting technique to keep the engine within the limits as the OAT climbs.
I have flown the Regent and the Remorqueur. They are very nice airplanes with an excellent view, and wonderful climb rates, especially the latter. I have friends who fly them regularly, in clubs, on tour, in towing, sightseeing, you name it. Never has anyone complained about heat issues and I haven’t observed any, nor can I find anything on the internet when I google the topic. Which I think I would, if this was a persistent problem.
When the temperatures were in the high 30s / low 40s last summer, I took the aeroclub DR400/120 for a 2 hour local to do touch and goes at 5 airfields. Just before leaving, one of the instructors ran over and said to keep an eye on the temperatures, especially in the climb. The engine had been having cooling problems and using a lot of oil recently. The club thought the reason for this was someone running the engine at redline in high ambient air temperatures. At reduced power and shallower climb it was a struggle to get over the Haut Folin (2,000ft in 9nm). In this case, the warning/advice was done informally by a quick word from an instructor. Shortly afterwards the DR400 went for a 100h service where it transpired the engine had to be replaced completely (I’ll ask what the problem was).
Engine defects aside the DR400 engine temperature issues at high OAT fall into two category’s CHT caused by high power at low airspeed or high oil temperature during the climb at best ROC speed for long duration.
None of these problems can’t be solved by good engine management practice .
I fitted a B&C full flow oil filter to my DR400 and because of the extra oil capacity it slows the oil temperature rise in the climb a little, I have been considering fitting a large aluminium heat sink around the oil filter, these are available from the Motor racing industry to see if this improves the situation during the summer.
