I’ve managed to replace the radiator in my 2004 Mazda RX-8, and now I have to put everything back together starting with new engine radiator hoses. Just like with the radiator, I did a quick comparison of old and new before installation and I’m really glad I did.

Cars typically have two hoses between engine and radiator, a RX-8 has three. Its top hose is divided into two parts joined by a metal mid pipe visible in the top left of this picture. The new upper front hose looks pretty close to the old one.

The new upper rear hose looks pretty close as well.

And this is where doing the comparison paid off: the lower hose is not an exact match. It looks pretty good on the engine side (left in this picture) but I see problems beyond that. The hose curvature is different but probably close enough to be bent into shape. The next two problems might be related: First, the radiator-side outlet flares out to roughly 5mm larger diameter than it should be, more than what the hose clamps can compensate for. Second, the flared section added overall length of the hose making it too long. I did a loose trial fit and jamming a too-long hose in place would cause unacceptable kinks in the hose.

Maybe it was a packing error? I double checked part number on the label (Continental 61098) and verified it was the intended product to fit my car. My next hypothesis is a manufacturing error. Somehow this hose wasn’t bent to the exact curvature and the radiator end was not trimmed to the correct diameter and length. The good news is that it’s a lot easier to cut a hose shorter than it is to cut a hose longer. I can fix it now rather than return this item and wait for a replacement to be shipped. I trimmed off the flared end so both the length and diameter is correct for a secure and kink-free fit against the lower radiator fitting.

The final challenge is compensating for curvature. The flawed shape wants to rub up against a sharp corner on the mid pipe bracket. That would quickly cut a hose open and not acceptable.

Fortunately Mazda engineers designed a white plastic clamp that clips between hose and mid pipe bracket so the lower hose is properly routed to avoid damage. Success!