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I am currently on a road trip with my family, riding in my Dad's 05 PSD. While towing through the hills, each time the engine reaches approximately 2750 RPM, and anything above 30 PSI of boost we here a loud whistle, I know the sound of normal turbo whistle but this seems like something else. Is there some type of over boost release valve? The tranny is in Tow/Haul if that makes a difference.
I don't know if the 450 engine is tuned differently from the 250/350, but here is my guess ............
Check under the hood for coolant coming out of the degas bottle. Seems that a whistle sound is common for leaking head gaskets. The coolant leakage will be indicated by a "spattering" of white spots where the coolant additives are deposited when the coolant evaporates.
Running over 30 psi boost seems high to me unless you are running a tuner or chip. If you do not have these, the turbo vanes may be sticking.
I had the whistling noise and it was the cat tubes behind the turbo. They fixed it and all is ok now. They also cleaned the turbo and reflashed it. Very happy with the new flash.
It is located below and behind the turbo. The tech said that they were totally plugged causing the whislte. As soon as I get the reciept I will post all the tech comments in my post. See the "All is well" post. Sorry to hyjack this thread for a second.