Originally Posted by
RVDT
Bleed air heater/demister leak - from memory the lines are alloy and water accumulates in the low point from compressor washing and the line rots from the inside out before the valve. It is not obvious as the line has a heat sleeve on it and you cant see the holes in it. 350 has the same problem. Fix is to run the heater regularly after each wash to vent the line and dry it. Again cap all the lines right at the engine and do a ground power check.
I have seen two situations with our twin squirrels here in NZ with similar symptoms. One was as above, we had a bleed leak caused exactly as described. The other was a crack in the hot section can... The cracked can was in an awkward place but identifiable during preflight. The bleed air was harder to find but fixed the issue straight away, From memory it was about a 40 degree split.
I have flown 5 different twin squirrels (F1 & F2 models) and yet to find one with two engines that match perfectly.