Purchased this car with 112k miles on it. Ran flawless up until now. Not one issue. My check engine light came on in my 2004 Mazda 6s and I was getting the P0421 code (Warm Up Catalyst Efficiency Below Threshold). After having it professionally diagnosed, they confirmed that it was the same code I pulled (wanted to know for sure that was the issue before replacing anything). Most common problem with this code is a bad catalytic converter. Mazda told me that the engine is burning oil due to highly saturated oxygen levels. They said this is clogging the cats. Of course, their solution is to just replace the whole engine. With parts and labor they wanted $7,700....are you kidding me?? Then they wanted another $3,700 to replace the over-priced catalytic converter. I mean if I was going to pay that, I may as well as just buy a new car while I'm there. What a joke. Timing chain cover leaks oil down onto the catalytic converter causing an odor of burning oil fumes into the cabin.

I have maintained this engine to a T. Changed the oil every 3k miles, changed the engine coolant every 3 years, changed all the valve cover gaskets, new coils and plugs every 30k miles with factory recommended gap spec, etc.

A special recommendation to everyone with the the 3.0 V6 2004 Mazda 6. REPLACE THE PCV VALVE AT LEAST EVERY 15-20K MILES. The part is only about 10 bucks and lack of replacement can be catastrophic to this motor. Very easy to replace too.

All and all I should have known better than to buy a vehicle with a Ford motor in it. The 3.0 V6 DOHC Duratec is a Ford motor. Ford itself is a joke. The exhaust system design is terrible on this car. Notorious for clogging and smothering the engine. Piss poor design by Mazda. This engine should have been recalled. But of course, car manufacture's never want to own up to their poor designs and flaws. We're stuck with the financial burden.