After reading this thread I tried this stuff in 2 of my cars and I even used 2-3 times the recommended dosage but it made zero difference in engine noise or anything else. Maybe it makes a difference if you use crappy fuel, but I suppose the B5 fuel that I use is already pretty good.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL