My UK Prius is 4 years old with 40,000 miles on the clock. The service book says replace the spark plugs every 4 years/60,000 miles. Do I need to change them now or will they last? It runs fine at the moment.
Not sure what they would put in yours, but iridium plugs last a very, very long time. In the US, the service interval is 120,000 miles.
Well, why is it that the US Prius has a 120K mile change interval in much of the country, but a 150K mile change interval in CA and other PZEV states? I suspect the latter change interval was established more for regulatory reasons and less for engineering reasons. I don't believe that the gasoline quality in the PZEV states (besides CA) is notably different from non-PZEV. Since the engine ECU will tolerate ~25% misfire before logging the misfire DTC P030x, I would err on the side of replacing the spark plugs sooner vs. later (my personal practice is to replace at 100K miles.) Seems silly to have unburnt fuel heating up the catalytic converter.
At 120k my plugs looked good. They car maybe have ran a bit smoother after the change but it could just be my imagination.
