Have a 2007 MX5 HTC and love it so I'm looking @ the 2025 CX5 for every day car but have concerns with the carbon build up on the intake valves due to the GDI system. Would using a GDI cleaner very oil change (5000ml)with low NOACK help or stop build up ? Also would the cleaner damage the cat ?

 

So, the internet has this exaggerated stated on a Skyactiv Mazda engine. While it is not as concerning as other engine it is still present, but most are very small amounts almost not even a concern. Now if there is engine problems like the oil control rings, valve stem seals and guides then that is a cause-and-effect condition and not from the basic engine design itself.

As for any so called GDI., DI (Mazda calls these DI) or any other abbreviation, the use of any liquid cleaner introduced into the intake system cannot have the results clamed because of the saturation time period fluid /liquid cleaners need to work effectivity. Also, any liquid in many platforms but specifically Skyactiv Mazda engine into the intake will have the ECU make changes in the engine operations based on less air going into the intake system being replaced by a fluid. Not the best idea unless you watch a few engines operation at the same time to make sure you are not creating a situation that is more negative than attempting to clean the carbon off the back of the intake valve? The other BIG warning is NEVER using any chemical cleaner that gets introduced either in the fuel tank or directly into the intake system that does not exactly say it is sensor and catalytic converter (CAT) safe.

Bottom line is don't over think this basically non issue with a Skiactiv mazda engine.
On any engine:
I do recommend that at 50k miles and then 100k miles to have the intake and combustion chambers scoped. And at 100k miles a compression and leak down test performed.

 

The only gasoline powered Mazda Skyactiv engine that I've seen dirty valves on is the base model Mazda 2. ( different engine on base model compared to Mid & high grade model Mazda 2)