PRODUCT DETAILS
Mishimoto Performance Aluminum Radiator (MMRAD-CIV-02SI) - 2002-2005 Civic Si (EP3)
The EP3 Si runs the K20, and anyone who's tracked one knows the factory radiator gets overwhelmed when you lean on it, coolant temps climb, and the cooling system becomes the thing holding you back on a hot session. This Mishimoto radiator fixes that: a dual-core aluminum unit that holds more coolant, sheds heat better, and won't crack like the aging plastic-tank original. It's a direct fit for the EP3, and it drops in whether you're chasing a leak or building the car for track days.
Why Swap The Stock One
Two reasons, and which one applies depends on how you drive the car.
If your EP3 is getting on in years, the factory radiator's plastic end tanks are a known crack-and-leak point, so this is the permanent fix, welded aluminum tanks with nothing to go brittle.
If you track or autocross the car, it's about capacity. The K20 makes real heat when you're working it, and the stock radiator doesn't have the margin for back-to-back sessions on a hot day. More coolant and better dissipation keep temps where they belong so you're not watching the gauge instead of the apex.
Dual-Core Aluminum
It's a two-row, 1.42" brazed aluminum core with TIG-welded end tanks, holding 1.58 gallons, more than stock. Aluminum handles heat and pressure better than the factory plastic-and-aluminum unit and sheds heat more efficiently, so both the construction and the extra capacity work in your favor. The polished end tanks are a nice touch too, they clean up the engine bay in a car where you actually see the radiator.
The included 1.3 bar high-pressure cap raises the coolant's boiling point, more pressure means it can run hotter before it boils, which is exactly the margin you want on track. A magnetic drain plug is in there as well, catching metal debris in the system before it circulates through your pump and engine.
It Also Fits The UKDM Type R
Worth knowing: this radiator fits the USDM EP3 Civic Si and the UKDM EP3 Civic Type R (2002-2005). Same chassis, same radiator, so whichever EP3 you've got, this is the one.
About The Fan Switch Port
A common question on this radiator, so here's the answer up front: it includes the proper M18x1.5 port for the radiator fan switch, located next to the outlet, same as the factory setup. It ships capped, so you'll uncap it and transfer your fan switch over on install. Nothing's welded over, you've got the port you need.
Manual Transmission
Note this radiator is for manual transmission EP3s. Given it's the Si (and Type R), that covers the vast majority of these cars, but worth confirming you're running a manual before ordering.
Fitment
2002-2005 Honda Civic Si (EP3, K20A3), USDM
2002-2005 Honda Civic Type R (EP3), UKDM
Part number MMRAD-CIV-02SI. Manual transmission. Direct fit, factory location. Have an 01-05 Non-Si? That takes a different radiator.
Who Should Grab This
This is for the EP3 Si or Type R owner who tracks the car and wants cooling that keeps up, or whose factory radiator is cracking at the plastic tanks. Dual-core aluminum that won't fail like the original, more capacity, the correct fan switch port, a high-pressure cap and magnetic drain plug included, and polished tanks that look right in the bay. Drop it in and keep the K20 cool when you're pushing it.
Fits: 2002-2005 Civic Si (EP3, K20A3, USDM) and Civic Type R (EP3, UKDM), manual transmission. Part number: MMRAD-CIV-02SI. Construction: dual-core (2-row) 1.42" brazed aluminum, TIG-welded polished end tanks. Capacity: 1.58 gal. Fan switch: M18x1.5 port included (capped). Includes: 1.3 bar high-pressure cap, magnetic drain plug. Install: direct fit, factory location. Warranty: Mishimoto lifetime.
2002-2005 Honda Civic Si
2001-2005 Honda Civic Type R