Recently, the nature of my turbo's whistle changed. It went from a whistling sound to more of a howling sirenish sound but didn't change its volume; it always stayed relatively quiet. The new sound was obvious though and I had read threads on here about how if a turbo made a noise like a loud siren (again, mine was not loud), it meant something was going bad. Well, I figured I wouldn't sweat it yet because power was good, economy was ok, and the noise wasn't so bad. Last night I cleaned my K&N (it was all blackish with crud caught in the fins), reoiled it, and today took it for a drive and it's like a whole new car. Best of all, the turbo noise reverted back to the original subtle whistling that I was used to. Any, point of this story is: if the sound of your turbo has changed slightly and you don't know why, change (or clean if you have a reuseable) your air filter.

Alex

__________________
1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

Must be nice to have a turbo that only sounds like a siren when the filter is dirty! My volvo sounds like a loud siren all the time (so do all the other D24T turbo's I've heard!)

Turbos "eat" huge amounts of air -- I change my filter very 3 months for the same reason -- the turbo starts to get louder and higher pitched and performance drops off.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!