Rusty, dirty water in radiator.

[jrj512]

PS - Do OEM's have enough cooling capacity for a boosted engine? I have no clue, just wondering.

The OEM radiator (and entire cooling system) seems to handle normally aspirated quite well. As long as my cooling system is 100% functional, then it keeps my engine cool in some very harsh track/autocross environments.

However, I am pretty sure you would need to step up if you are using FI.

[titanescape]

I don't track mine and I didn't have any heat issues before when I was driving it daily. I could run the AC on a 100+degree days in traffic and be fine. The only time the temp would go up was if I was tailgating and the flow of air was gone from my front end. That was before it sat up for a while and all this gunk appeared. A new radiator was on the list of upgrades just because I figured it needed on any way.

Thanks for the Super Flush link, very cool!

[Bob_MX5]

You must work for a radiator company!! Just kidding :)

I really have no idea how old it is. I originally bought the car from Tom(RIP) at Miata Technologies so there's no telling. I'm guessing it has been replaced once because it doesn't look like there's a 123k miles on it. I'm going to do pretty much a complete refurb on the car(just project work with the kid) so might as well replace it. The interior is in great shape just want to get all the mechanical up to par. I will take your suggestion though to flush out the system and then put in the new rad as well as hoses.

You can't tell by looking if the rad is going to fail. As they age, the black plastc top turns color to olive-drab green and then it fails. The time between color change to failure is unknown so most recommend replacement when you notice the color change. Why? Because all the ones that failed were olive-drab green.

But they also last for years after the color change so color is not a good indicator of failure. My personnal rule of thumb for the NA is replace at 20yrs or 100k miles.

Bob.