Spark Plugs at 40k ?

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CX-9 GT 2019
For a non-boxer turbo 40k interval does not look like an issue at all...

My '15 WRX has 60k interval for spark plugs. But its worth changing early. I stretched it to 60k and got ~2 mpg jump and better idle when I finally changed them.
 
V
Mazda CX-9 Grand Touring 2016
The Red Line fuel system cleaner is good stuff if your engine needs it. The only way to know if it needs it is to spend the $12 and use a bottle. Can't hurt (except the $12) and might be a little help.
 
Go to the dealership only for warranty repairs or repairs too complex for an independent shop. Any shop can do spark plugs, and it'll be much lower cost than the dealer. You know the dealership will also try to scare you into additional repairs as well.

40k would also be a good time to drain & refill the automatic transmission for owners who expect to have their car for a few hundreds of thousands of miles. Modern ATF is probably good for 100k. Draining and refilling changes something like 40% of the fluid, so doing it periodically will keep the fluid fresh and protective.
2nd Generation Mazda CX-9 (2016 - Present) with SKYACTIV TECHNOLOGY will have lifetime transmission fluid that only requires changing should a critical component or the whole transmission need to be replaced. Spark Plugs needs to be changed every 40K miles to avoid misfires because the engine is turbocharged and has a high compression ratio.
 
The owners manual calls for plug changes at 40k miles. I was commenting that 40k seems exceptionally early for that.
Changing spark plugs @ 40K miles are pretty common for turbocharged direct injection engines to avoid misfires especially the SKYACTIV TECHNOLOGY we have in our CX-9 which have a very high compression rate for a turbocharged engine.
 
V
CX-9 GT 2019
2nd Generation Mazda CX-9 (2016 - Present) with SKYACTIV TECHNOLOGY will have lifetime transmission fluid that only requires changing should a critical component or the whole transmission need to be replaced.
There were many cases where car manufacturer declares lifetime ATF fluid, but gearbox manufacturer declares 40-60k miles :) Do Mazda use their own transmission or 3rd party?
 
There were many cases where car manufacturer declares lifetime ATF fluid, but gearbox manufacturer declares 40-60k miles :) Do Mazda use their own transmission or 3rd party?
2nd Gen Mazda CX-9 (2016 - Present) uses the SKYACTIV 6-Speed Transmission developed by Mazda.
 
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