Might be time for a replacement radiator?
 

For about the past year or so, I've been losing coolant ever-so-slowly. Maybe a cup to cup and a half every 3 to 4 weeks.

I was planning on replacing all the coolant hoses, thermostat and cap in the near future. As a matter of fact, I just placed an order with Mazda for all these parts, but some are on back order. But, than it occurred to me that maybe the radiator is the culprit.

A number of years ago, I went through this same exercise of adding some coolant about once a month. I turns out that it was exactly 15 years ago to this date that I replaced my original radiator. I bought a replacement Mazda radiator from Malloy Mazda (Ray Crowe) for my S5 N/A coupe w/ MT in April 2005. On my original radiator, one of the side tanks was leaking ever-so-slowly. The side tank probably leaked only when under pressure and the leak was so slow that the coolant would evaporate making it hard to locate the leak. No puddle of coolant on the ground. I remember that I had a hard time finding that leak, but do remember that one side of the radiator was wet.

So, it's been exactly 15 years since I last replaced my radiator. I'm thinking that maybe my radiator has possibly sprung a leak again. Is it reasonable to say that 15 years is about the average lifetime for the stock Mazda radiator?

What are my options for a replacement radiator, other than a stock Mazda radiator? Is a stock radiator even still available from Mazda? Looking at the Mazdatrix website, they've got the Toyo aluminum radiator in both single and dual pass, a Mishimoto aluminum radiator and it looks like they've got an OEM replacement radiator too but I'm not sure if it's an original Mazda part. There's Rockauto too, but it looks like they've got two off brand (CSF and APDI/PRO) radiators. I'm not sure if I'd even want to put that Rockauto crap into my car. In any event, I'm looking for a plug-and-play replacement radiator requiring no modifications. I want to keep the stock radiator mounts and fan shroud. Any suggestions on plug-and-play replacement radiators?

Koyo N Flow is a solid choice but you have to cut the plastic intake piping a little to fit with the radiator cap. There's a lower grade Koyo replacement that works with the OEM intake.

You will have to reuse the radiator brackets that are on the oem radiator.

I second the Koyo N-flow recommendation, I've been very happy with mine since around 2011. It is pretty close to a drop-in installation in my S5T2. Mechanical mounting simply uses the factory side brackets from the old OEM radiator and it drops in exactly like stock, upper & lower hoses fit perfectly, and there's a threaded hole that fits the stock low coolant level sensor, along with another bung & plug on the upper hose outlet that serves as a handy air bleed.

But because the radiator core is significantly thicker than stock, there are 2 modifications you'll need to deal with (might be slightly different on an NA car, but I don't think so):

1. Chuck the plastic cold air inlet duct that runs along the top of the radiator to the stock air box. It will bolt on fine, but you'll find you can't close the hood with it there because it sits higher as a result of the thicker radiator core.

2. There's much less clearance between the plastic fan shroud & OEM mechanical fan (again because of the radiator's core thickness), so managing to get the shroud not to interfere with the fan blades AND getting the plastic shroud to securely attach to the radiator using the OEM attachment points involved a little bit of strategic trimming of the plastic shroud in a few spots along its mounting surfaces with a Dremel, and the use of a couple of longer bolts and spacers/stand-offs to clear the thicker core. It's pretty obvious when you're looking at it.

Tip - Before installing the radiator in the car, install the factory brackets to the new radiator and then test fit the shroud to the new radiator/bracket assembly - that will make it easier to figure out where you need to cut away some plastic and size the necessary spacers and longer bolts. Once you have that figured out, loose fit the shroud to the radiator - that will give you enough wiggle room so you can maneuver the radiator/shroud as a unit over the fan, and drop the radiator into its mounting points & secure the radiator mounting bolts. Then you can move the loosely mounted shroud around a bit to ensure it clears the fan blades before tightening down the shroud's attaching bolts.

Koyo revised the N-Flow sometime within the last 3 years or so, replaced with a superseded part number; the core is actually thinner, but supposedly more efficient than the older model you and I have. I don't know how much effort is involved installing this newest model, but I would imagine a little less than what it used to be.

In my experience with various vehicles it seems 10 years or so is about the lifespan on plastic end tanks before they crack and start leaking.

I have a Godspeed which was I think a Chinese copy of the Koyo N-flow. Doesn't look like they are available anymore. There is one that is similar that's branded GPI and looks like the brackets are part of it. Godspeed used the stock brackets like the Koyo. I have been happy with it but I already had an electric fan and cone filter so I had none of the fitment issue you may experience. My vote if you're on a budget would be the GPI and take the money saved over the Koyo and buy a good electric fan and be done with the factory plastic shroud and clutch fan. If money's no issue then the Koyo N-flow and Efan. It makes anything on the front of the engine like belt changes, etc. so much easier.
Also I had one of those like Rockauto sells. May have been a CSI. It's a brass replacement and by my autometer gauge did not work near as well as this Godspeed. It didn't work as well as a factory one either. So I'd avoid those.