[Graeme Smith]

Orv, has anyone ever done a study using string and video to show how the air flows through our ships in a hover and forward flight?  Seems like we could do a lot of useful modifications that would improve cooling.  Experimenting can lead to the issues you experienced.  Graeme has done some interesting stuff in this area, but it seems like we should be able to get more cool air to the engine and radiator without extensive modifications.  

I still can only get about 10 minutes of hover training done for my bride before we reach redline.  I have purchased an electric water pump, but I am not convinced this will fix the problem and this is a big modification to undertake only to find out it didn't fix the issue.  When I hover without any cowl, it seems to stay cooler.  This tells me I have an airflow problem, not a water circulation problem. 

I think before I do the electric water pump, I am going to cut holes in the upper rear cowl to allow more cool air direct to the radiator.  Would be nice to have a study show the airflow rather than experimenting.  But the helicopter has a big EXPERIMENTAL label on it, so....

The problem is sucking in hot air from around the engine and then trying to force it downwards through the radiator is simply wrong wrong wrong, and to achieve any resemblance of making it work RW over the years' have changed the radiator shroud, introduced a blade tip ring to minimise the tip clearance and they have have increased the fan pitch, (and increasing the fan pitch created another problem in that the low pressure at the centre of the all centrifugal fans, increased, such that the centre section, below the fan , actually sees a reverse flow, so that high flow rates appear at the perimeter of the radiator but slowly diminish as you move towards the centre of the radiator where the flow then goes upwards into that low pressure below the spinning fan, so the air that does get through at the perimeter of the radiator absorbs some of the heat but then travels upwards through the centre of the radiator heating the coolant on its way. all of these are improvements (except the increased fan pitch) but do not solve the fatal flaw in the design.

Do what all cars do, put the fan behind the radiator and use the incoming air caused by the car going forward to get the coolest air possible to flow through the radiator, and yes it is a big project to fix the design but the results are very impressive,
1 in saving the 10HP+ that the belt driven fan uses, (rule of thumb in helicopter performance, 1hp lifts 10lb)
2 using forward flight to capture cool outside air and flow it through the radiator.
An electric fan is fixed to the bottom of the radiator and that draws air through the radiator keeping the coolant correct in the hover, (the fan cycles in a hover) then in forward flight the fan remains off as the outside scoops are doing the work of capturing the air and directing it through the radiator, 

I have done this mod on 3 RWs and the results are very impressive, (confirmed by an independent flight instructor who was very familiar with the RW performance) in my current project I went to the trouble of making moulds to create the outside scoops if there is interest I could get some made and then all a builder would need to do is fiberglass the scoops into their side panels and fit the shroud over the existing RW radiator.

You do not need more power for the RW what you do need is remove the parasitick power that the fan uses and use outside cooler air to flow through the radiater. 
PS I do fit an electric fan in the dog box attached to the 2 angled down tubes to evacuate the the engine bay, it is controlled by a temperate sensor and again remains off in forward flight.