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I always used 95 gas, or 98 if at a gull station.
It’s a Mazda CX-5 2013 I think and I’ve only just read the manual for another issue and saw it takes 91!!!
This car cost me $6k in repairs last year and used to do 800km to a tank. It now does 650 so it’s nearing the end of its life but I can’t afford to replace yet.
With the efficiency getting worse and worse can I start using 91 after years of 95 and 98 or will what remains of it crumble if I do that?
Have had efficiency tests done and they don’t find any reason for it failing.
I can't see any reason for a vehicle designed for 91 octane fuel having any issue if switched from higher back to 91.
You may find that over the years the intake system has a dirt build-up and an intake system and throttle body/flap clean might help a bit.