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We have an 04 2.3L Mazda 3 we purchased used. Shortly after we bought it, the code for the thermostat came on. I replaced the thermostat with an aftermarket one. Big mistake! The thermostat failed on a trip and overheated the motor, blowing the head gasket. Had the head gasket replaced and the mechanic neglected to change the harmonic balancer bolt. Apparently a TSB item, but since he wasn't a dealer, he didn't know about it. This caused the motor to go out of time and damage the valves. He repaired the motor at his cost. Since we got the car back, it runs like crap when you first start the motor on a cold day. Car runs bad and the colder it is outside, the worse it runs. Once it's warmed up, it seems fine. Anyone know what I can look for on this issue? I took it to the nearest Mazda dealer which is 60 miles away. They claim to have put it in the computer and say nothing's wrong. We've pulled the valve cover and double checked the timing and it's spot on. My guess is that when the dealer had it, it was warm from the drive and everything appears to be fine. There is no check engine lights. Thinking it has to be something with the cold air system, but not sure where to begin. any help would be appreciated.
Also, there's a soft whine under the hood that we traced to the fly by wire system. When we shut the car off, the whine continues for a few seconds. Is this normal? Do those things make that kind of noise on a normal basis? Being new to the Mazda and new to the fly by wire setup, I'm not familar with this at all. Just doesn't sound right to me.[/b]
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Mazda's use a timing chain, not a timing belt. It is possible that your timing chain is making noise. I have heard this sort of thing in engines after 30,000 miles. It typically goes away when the engine is warm or after stopping and starting the engine. Considering your case I'm not sure how bad yours is.
A "little" whine is normal...assuming you cannot hear it when the hood is closed or when you're in the car. If you have a loud whine I'm not sure what is going on there. I can say that the Mazda3 has a very delicately balanced power system. I once tracked down a problem with the ac cutting out to a bad battery [even though the rest of the car worked fine]. If you have any bizarre problems test the battery and work forward.