aleekat

You posted to a 7yr old post. Really should have started a new one. You didn't give the year but this sounds more like a dealer parts department question. They're usually pretty helpful.

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2001 Workshop & Wiring Diagram

If you have no oil in your coolant and no coolant in your oil, then suspect bad water pump. Get a pressure tester from local autoparts store with their loan a tool program. They build pumps with a weep hole when the bearings start to go bad the pumps leak at this hole. It's on the underside of the pump.

Here's 12 pages of the same issues. Maybe you'll get some ideas. P0400

You need to check voltage at the battery when you try and start it.

Maybe something here

Maybe here: Workshop Manual

With that mileage I would be concerned about the transmission.

Before you throw anymore parts at it. What are the codes? Shop Manuals

I ask about the rpm change because there is a one way check valve in the main brake booster hose that can go bad. You can't see it and lots of folks don't know it exists.

Any hissing or rpm change when stepping on the brakes? You can check this in park at idle.

If you are asking about removing the alternator. PBlaster on the front pipe nuts to remove than you can drop the alternator out. Pipe does not need to be removed just loosen up to move out of the way.

Any hissing or rpm change when stepping on the brakes? You can check this in park at idle.

Thanks for posting back.

weep hole at the bottom of the waterpump. signs it is going out. Edit: Get a pressure tester.

a/c drain line. normal

Shop Manuals

I can only suggest check over every fuse. Edit: I would try and narrow down whether it's spark or fuel. Plug removed and place near the engine and look for spark. Or starting fluid. So you can decide the course of action determining why one of those is missing.

A cheap check would be look for the test port in front of the catalytic converter. Remove it and drive around and see if it runs better.

The problem is Mazda changed all the part numbers after 97 even if it crossed over. All you can do is check with the seller about return policy.

https://www.google.com/search?q=GD7B6997580&rlz=1C1CHBD_enUS724US724&oq=GD7B6997580&aqs=chrome..69i57j69i60l2j69i61&sourceid=chrome&ie=UTF-8

Yep sounds like a head gasket. Your buddy thinks the Mazda has xmns oil cooler lines that share the radiator, not so. Other cars do this. https://www.youtube.com/watch?v=5zpNjYmmiYY

I just remove the 3 nuts up front. Pulled the exhaust down and was able to maneuver the alternator out.

Good deal.