I'm fresh out of a week recurrent training from an overhaul shop, the rr 300 is the old technology back end with a centrifugal compressor up front.the reason for the cool down is to get the core below 450 degrees which is where carbon forms. I like 3 minutes on our R2 as we had lock up at times with 2 minutes cooldowns, and none on the 3. making sure the 6&7 struts upper and lower are cleaned well on the inside helps also , also the oil tube with the stem out the top is the new style and thus the 200 cc oil flows we see..

lamanated:
Did you submit an SDR on the lock up?

Oil manufacture as opposed to type can make a difference.

In the early 80's Hughes 500D's were delivered standard with Mobil Jet II.
In the UK at the time the standard oil used by most operators in the Bell 206 was Aeroshell 500.

A number of operators changed to AS 500 in their 500D's for commonality.
It became apparent that although both oils were to the same Mil Spec AS500 made far more carbon than JET II. The oil filters would come out dripping carbon at scheduled maintenance. This was then coupled with a number of engine failures all on AS500
aircraft.

This problem only occurred with the 500D the early C model did not seem to have any carbon issues.

The C30 in the S76 was even worse. Again AS500 was the oil in use. One UK operator used to remove both turbines from one of it's fleet of six every weekend for a workshop strip and decoke. This was a continual process in an attempt to prevent turbine bearing failure.
At this time Sikorsky added armour plate to the engine bays to protect the airframe, about 20 kgs a side.

In the end they operated all six with a different oil as a research programme, bit of a logistical nightmare.. The cleanest oil was Mobil 254 and that was fixed as the company standard.

An earlier post refers to a graph issued by Allison. This is actually a peak soak temperature plottted against idle time. The graph was issued in 1976 and I got my copy on my course in
1979!!!!!!

To cut it short the hottest area is the power turbine strut.

0 seconds at idle 371 degrees centigrade
30 secs 304
60 secs 260
90 secs 238
120 secs 227

At 2 mins the graph goes more or less flat so no further gain from continued idle running.
A drop in core temperature of about 150 degrees C over the two minutes and enough to give the oil a fighting chance!!!