Engine radiator MISHIMOTO or Koyo

the Koyo certainly looks much better. You won't notice any difference in cooling between the two.

Later I came across a deal for a Mishimoto radiator and had that installed. I’ve had no issues with my Mishimoto, and I bought it before seeing most recommending the Koyo Radiator over Mishimoto.

I'd go with Koyo for price and ease of install. My reservoir hose nipple broke on my OEM radiator (OEM has plastic tanks) so I went with all aluminum for durability. My RX-8 also only drives on race tracks, so the extra cooling is nice.

In my particular situation I went with the Mishimoto radiator. Idk why it gets so much flak. Had no issues with install and it has been great. Now I use my 8 for autox so I needed the extra cooling. I can say that last weeks event it was 89 degrees out and even after a 2 hour drive and fielding for 4 mins to make my run; my ect was 200.

I'd replace it with a fully aluminum one just because of that pesky plastic nipple that's prone to breaking. Koyo makes a good one.

I’ve had really good luck with Koyo radiators in the past as a really good replacement. The couple all aluminum radiators I’ve had, I really wasn’t impressed with the quality of construction.

I went Koyo. For me even with a stock engine its worth it not to have a plastic seam to worry about.

I put a Mishimoto rad in the R53 on the same terms as you @whalemingo - and only learned of Mishi's QC decline after I put it in the car. So far, it's been just fine.

stay away from mishimoto, their radiator quality is sub par

The Mishimoto all aluminum radiator (2 core) started leaking this past January (86k miles) in the top left corner (if you are facing the grill). From what I can tell with reviews, I was lucky to get 18k miles on that radiator.