Life expectancy of a 2003 Mazdaspeed Protege?
 

How long is a piece of string?

I've seen engines last 300,000kms. I've also seen people kill a engine in 50,000kms from no servicing.

I bought a 2003 a couple of years ago for my son. It had about 150k on it. I see no reason why it won't last a long time to come. They have that rust issue just ahead of the rear wheels though. Too bad.

Just noticed you said Mazdaspeed. No idea on that one, but FWIW on Denver craigslist I see a lot for sale that need engines. I've always assumed that's because they're all owned by 20-somethings who drive the hell out of them.

MSP My dear old Friend
 

My 2003 MSP has easily gone 150,000 miles. Compression is still about 164psi for each cylinder with no noticeable decay. In 2015 I put a Garrett GTX3076R with 60mm hot and 80mm cold and set the boost at 13psi (with slight adjustment to VTSC solenoids so no slamming) - peaks at ~16psi. Transaxle was replace due to engine power increase to 340hp twisting the transverse ball welds off of the gear. Rust has damaged the drivers rear tub and rear fenders near the bumper skin, otherwise it is almost 100% clean. 0-60 at 5.2s. I put new OEM bearings on all 4s after filling each with PTFE type Marine grease to each using a hypodermic needle - wheels spin super easy and silently now. Too many other modifications to mention here. I drove that thing fairly hard, all over the US and CA. Lots of great memories with that car.
I just sold it for $1,500 to a younger driver, who seems to understand the basics of the car. Hope it brings him many years of joy as it did me. See you on the Tesla forums now.

We have some in Australia on the 400k mark. Basically engines will last as long as you maintain it. Thats why i dont care about mileage when I look at second hand cars. I pay more attention to the owner. If they give me a hint of noobness I will low ball them to the ground.

I ran my A1 Audi from 0 to 170,000kms and my suspension engine and transmissions was still in tip top shape cause of how I baby the car over speed bumps and avoid potholes. I also changed the oil as soon as I heard any unnatural noise coming from the hood which was usually around the 2k-3k mark. Thats why the lady who bought it from me didnt care about the mileage on it. She already knew how good i was with the car as soon as she saw it because of all the other audis she had inspected. Mine still looked brand new inside and out and she picked up all my spare parts which would keep her going for another 3 years.