I can't recall if I already posted/shared this. This is from the Mazda 3 forum. I'd love to know if using Valvoline Modern Engine would have made a difference. "so here we go... PURPOSE: when mazda designed and started manufacturing the skyactiv-g engine that is in all of our 3rd gen cars, they decided to use direct injection. as we all know, no fuel hits the back of the valves with this design. many manufacturers have had problems with buildup of carbon on the intake valves causing loss of power and fuel economy. mazda was very clear that their design would allow the valves to run much hotter and prevent buildup of problematic carbon. the purpose of this is to try and determine if that is true or not. i think you'll find the results interesting. ABOUT MY CAR: - 2015 mazda 3, built in mexico - i purchased new, original owner - 2.0L skyactiv-g, manual transmission - mileage at the time the images were taken is 130,470 km HOW IT IS MAINTAINED: i perform ALL of my own maintenance and have since day one. as per the owner's manual, oil changes are every 8000 km. this is the schedule specific to canada and i have adhered to it strictly in both distance driven and time. in fact, i tend to do my maintenance a little early since i do not want to go over. i use castrol edge 0W-20 and ONLY this oil. it is considered a synthetic oil. i also use the OEM oil filters from the dealer. the filter is changed at EVERY oil change. in short, i take good care of my cars. why castrol? i can get it cheap and it's easy to get here. it is specifically recommended in the owner's manual. all other regular maintenance items are kept up to date with just as much rigor. air filter, regular checks, etc. injector cleaners, engine shampoos, seafoam and other such snake oil is NOT used. EVER! your fuel already has detergents in it, so i consider it unnecessary and potentially harmful. if your clothes come out of your washing machine clean, adding more soap isn't going to do any good... HOW IT IS DRIVEN: i generally drive 20km/h over the speed limit on highways and 10km/h over in the city. conditions permitting of course. i commute to work, my drive is 95 km (yes i googled it). drive time is about an hour. most of my use is highway, but i do some city driving where i live. there are a good deal of hills on my drive and the city i live in is built in a big valley. i tend to accelerate fairly hard, but i'm not completely insane on the road. we'll say 'spirited' as mazda puts it. normally, i'd say my engine doesn't see much beyond 4000 rpm too often. i use cruise control often. this car is driven in ontario, canada. as such, it sees temperatures over 30ÂºC and under -30ÂºC. we see all extremes here. i use a block heater in the winter to help it out. winter time i have a set of winter tires which negatively impact fuel economy. FUEL: i usually fuel up at the Esso around the corner which is considered a 'top tier' fuel station. i put regular 87 octane in as the more expensive grades doesn't do a thing for this car. MODIFICATIONS: none. completely stock. not even an oil catch can. SYMPTOMS: none that i can detect. i suspect i've lost a little power and fuel economy since it was new, but nothing too significant. this is purely exploratory. my car does not burn oil - at all. typical fuel economy is roughly 600km per tank. works out to somewhere around 6-7 L/100km. do note that speed has a HUGE impact on the fuel economy in this car. if i drive slow (the limit) i can drop the fuel economy under 6L/100km easy. especially if it's an 80km/h highway. all the hills i drive have an effect. i try to coast in gear to take advantage of the deceleration fuel cutoff as much as reasonably possible. fuel economy isn't so great in the winter as expected. in short, i am probably in the best position to look for carbon. regular boring joe driving with nothing that could potentially upset the results.