Engine radiator Koyo or OEM BMW

just replaced rad and all soft and hardlines with oem hoses and koyo rad. gives me a lot of reassurance in this LA heat. Great upgrade

The Koyo Rad needs it's own custom cap as the OEM won't fit but man does track city daily without issue and fits OEM fans it's a must have.

OEM radiator. Replaced radiator on visit 5 (today). Bmw closed loop network is what eventually led to the radiator being checked as they’ve seen aftermarket radiators actually cool the cars too much, therefore sending the tstat fault in cold weather (this issue occurred first last winter for me, then again 5 times this winter.. all same fault code). Confidence that this is the root cause fix seems to be high so fingers crossed I won’t be updating this in a few days.

The previous owner had replaced it with a really cheap plastic tank one. It started leaking about a month after I got the car so I spent the money and got an all aluminum Koyo. Its a happy miata now.

Koyo rad hands down best aftermarket replacement.

I would recommend the koyo radiator with stock fans. It’s been 3 years with mine zero issues it’ll run cool in 120 desert.

I would recommend a full aluminum koyo radiator. There are pricy but they fit like OEM and use the OEM fans. 2 years later with 15k and no issues.

Koyo has better fitment than Mishimoto tho, I think that's more important as they both have good warranty. One thing to note is the only radiator Koyo has for the DE that is OEM design is the larger one, the smaller one it the cross flow, which is better performance wise but puts the radiator cap on the passenger side. That's the one I currently have.

Im in AZ, and I was hitting up in the 225+ coolant after a Grimmspeed FMIC, and so I went ahead and upgraded to a koyo. Now I’m staying around 196-206 depending on situations. Highest I’ve seen is 208 or so.

I recently installed a Koyo radiator in my s13 to replace the stock one that had been leaking. I bled the air thoroughly when I filled the system with a spill free funnel and the bleed screw on the water outlet. Even after doing this, my car started overheating intermittently after driving around for a bit. When I stopped, the upper hose and radiator were very hot but the lower hose was cool to the touch. I tried to bleed more air out of it with the spill free funnel, but no air came out, and the water in the funnel started getting hot and overflowing. I pulled the thermostat to verify if it's functioning properly and it is, also it's the type that will stay open in the event of failure. This might seem silly, but I feel like the thermostat is closing and opening because the radiator is cooling too well.