I think the only things that make a real, immediate difference ar the "direct" applications where the cleaner is injected directly into the injection system. For gassers, I have a 3M injection system cleaner that plumbs right into the fuel rail. For Diesels it's the purge...

The 3M system cost me around $200 and will do nearly every make of car while the Diesel purge setup was basically free.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250