Good advice Arthur. We will often change them when we change plugs for two reasons. The first is we get blamed when the POSs can't take the physical handling of removal to access plugs (or head gaskets). Second when they are working there ain't snowballs chance in H of diagnosing them so you are doubly screwed. The shop gets blamed for causing the problem and then gets blamed for being stupid when they can't ID the non existing problem when it comes back, working for the moment.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician