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I've read about and seen videos of direct injection engines (other brands) with dirty air intake manifolds and cylinder head ports, causing loss of power and efficiency, with costly cylinder head rebuilds. Much of the dirt comes from PCV gasses entering the intake. Since the fuel/air mixture does not pass through any internal passages, the solvent properties of the gasoline can not maintain a clean, smooth surface. I've been able to clean the intakes on other cars I've owned (without direct injection) by removing the flexible intake tube between the mass airflow sensor and the air filter box, spraying Gumout or intake cleaner while someone revs the engine. Today I removed the air intake from the air filter box on the M6, and was surprised to see anoter filter, mostly a fine metal mesh, embedded into the top of the air cleaner box (fits over the air filter). I tried to pry it out, no luck. Has anyone had any problems with dirt and PCV crud building up inside the intake manifold and intake ports in the head? My car has 119,000 miles, with no performance, fuel economy or driveability issues. I'll leave it alone for now, but want to prevent future problems if possible.
 

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This is a topic which has been discussed rather thoroughly on this forum, along with others. Mazda engineers decided to route the coolant passages away from the intake ports of this engine in an attempt to keep that area of the engine hot enough (400F) to effectively burn off any potential deposits. They've also done something with the PCV valve except I dont recall exactly what. I think it sort of acts like an oil catch can.

All I can suggest is to limit the amount of short distance city driving you do with the car and occasionally hit 5000rpm, maybe about once a week so that the intake ports become hot enough. Revving the engine 2 or 3 times in a row to near redline will burn off nearly all deposits. You can also consider purchasing an oil catch can from corksport. Now I am aware this is a DI engine, but for some reason fuel system cleaner seems to have really helped. I drive my car pretty reserved most of the time but when I do rev it out; the exhaust smells horrendous, presumably due to the carbon clearing out possibly from the fuel injectors as well. Full throttle acceleration seems to work much more effectively for this purpose when I used fuel system cleaner. Another thing I would suggest is to use at least 5w30 oil as it limits the amount of blow by your engine produces, and thus, reduces carbon build up as well.
 

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Discussion Starter #4
This is a topic which has been discussed rather thoroughly on this forum, along with others. Mazda engineers decided to route the coolant passages away from the intake ports of this engine in an attempt to keep that area of the engine hot enough (400F) to effectively burn off any potential deposits. They've also done something with the PCV valve except I dont recall exactly what. I think it sort of acts like an oil catch can.

All I can suggest is to limit the amount of short distance city driving you do with the car and occasionally hit 5000rpm, maybe about once a week so that the intake ports become hot enough. Revving the engine 2 or 3 times in a row to near redline will burn off nearly all deposits. You can also consider purchasing an oil catch can from corksport. Now I am aware this is a DI engine, but for some reason fuel system cleaner seems to have really helped. I drive my car pretty reserved most of the time but when I do rev it out; the exhaust smells horrendous, presumably due to the carbon clearing out possibly from the fuel injectors as well. Full throttle acceleration seems to work much more effectively for this purpose when I used fuel system cleaner. Another thing I would suggest is to use at least 5w30 oil as it limits the amount of blow by your engine produces, and thus, reduces carbon build up as well.
This car has about 90% highway use, 65+ MPH, long distance. The rest is country roads or suburban. Oil changes with Mazda 0W-20 w/Moly & Mazda oil filters (cost less than other brands at auto stores) So, that must be enough to keep the crap from building up. Also been using fuel treatment cleaner about 1/month. I'm gonna just keep the same regimen until I see something bad (not anticipated).
 

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This car has about 90% highway use, 65+ MPH, long distance. The rest is country roads or suburban. Oil changes with Mazda 0W-20 w/Moly & Mazda oil filters (cost less than other brands at auto stores) So, that must be enough to keep the crap from building up. Also been using fuel treatment cleaner about 1/month. I'm gonna just keep the same regimen until I see something bad (not anticipated).
Highway driving is very good for any engine. I wouldn't worry about carbon buildup. However, to me sounds like monthly fuel system cleaner is a tad excessive. That stuff contains detergents which wear out your fuel lines and what not over time. I think every 20+k miles is a better solution.

I'd suggest giving 5w30 a try for one interval and see how the engine sounds/feels. :)
 
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