My 2005 manual Mazda3 is going through 2 quarts of oil a week. There's no smoke or leakage of any kind. Any suggestions on what it could be?
The engine is toast, and your O2 sensors and catalytic converters will be as well soon. Read some of the threads about oil consumption and read the threads about engine swaps. The early mazda3 engines will eventually start 'consuming' oil and there is no fix.
Sorry to be the bearer of bad news, but swapping a mazda engine with a Ford Duratec engine that is more reliable is the way to go. You'll get a lot of support on these forums as many have done the swap and already done all the hard research. I just completed my swap and it feels great!
p.s. New model Ford engines are way more plentiful and way cheaper and have much lower mileage than older Mazda engines. 2.0L/2.3L/2.5L Ford and Mazda engines share the same block, so they are very compatible with each other.