Hi, I looked with a borescope inside all my cylinders, and there is identical carbon (I think) buildup in the same spot on all pistons. I dis not check if it was beneath the intake or exhaust valves.

The car is a Mazda 5 from 2007 with 1.8L petrol engine, 5 speed manual transmission, 100 000 km.

Can anybody tell me what is causing this?


This picture is upside down with the piston at the top.



This picture is upside down with the piston at the top.

 

And/

That is really not bad for the mileage on the engine?

Its more the valves that are the big concern. Go back and scope them and post the pictures.

BTW a lot of that piston carbon can be burned off with an Italian tune up. I am not suggesting you do it but technically it does a surprisingly good job.

I also notic you have a cyclnder glaze. That is another thing the aforementioned MacGyver service can cure and by breaking the cylinder glaze you will bring back lost power caused by a cylinder wall glaze.

 

Thanks for the input! Here are some pictures of the valves, don’t know which valves these are unfortunately.

 

The only way to take your pictures and to verify the finding is to correctly do a compression test. Then compare the results in which you may need to repeat the compression test with a wet test method.
And after and comparing the results a leak down test may be warranted if not simply added informational to your compression testing?
naturally to add the best information a short oscilloscope data run will show you each cylinder performance levels.
Take all this and you can get a BIGGER idea if the carbon is affecting the performance of your engine.


The pictures (I wish you would correct the position before posting) IMHO based on poor quality pictures supplied simple show average carbon build up.

 

Thank you for your input!