First - why do you want a coolant reroute? Because when Mazda went to put the B-series engine in the Miata, they decided to put the thermostat on the front of the engine for packaging reasons. This means that a large portion of the coolant never goes through the back half of the engine, leading to poor overall heat transfer and problems with the #4 cylinder running hot. Moving the thermostat to the back of the engine, where it's supposed to be, solves these problems.
We've been selling reroutes for years, and they've been gradually getting better. This one has been designed and tested for maximum flow. We went through multiple designs testing the flow to make sure this is actually true. Our flow area is 8% better than stock, 11% better than the first reroute we sold and 5% better than our previous offering. We even tested flow through the heater so you'll stay warm.
It puts the thermostat right into the head where it belongs so it reacts quickly. It's completely compatible with EGR pipes - not "it works if you hit it with a hammer" compatible, but done right. It's fully electrically conductive so your temperature sensors read properly, and it has a spot for an aftermarket sensor. The reroute housing is a single piece to avoid leaks. Even the thermostat is an off-the-shelf 195°F unit so you can run a different temperature if you'd like (we sell a 180°F unit but find it's not necessary for most and can cause check engine lights in some cars). There's a bleeder screw on the top of the housing so you're sure you don't have air bubbles. And it includes a bracket to properly secure the upper radiator hose. So it's the best reroute you can buy already.
But the big difference is the turbocharger. We worked with the engineering department at Colorado Mesa University to map out all the cooling factors of the Miata engine, and discovered that a water-cooled turbocharger will increase the temperature of the coolant flowing through it by as much as the rest of the engine put together. To make things worse, this very hot coolant is mixed right back into the engine coolant, with no chance to cool down at all. Obviously, we decided to address this. First, we dropped the amount of flow into the turbo - they're cooled by the engine oil during operation, they really only need the water cooling when the engine is off and they use thermal siphoning to get it. The big difference is the plumbing, though - the water coming from the turbo is now plumbed back into the water heading into the radiator so that it's cooled before going back into the engine.
Choose the NA or NB kit according to the intake manifold that you're using - the only difference between the two kits is the hose bracket, which bolts to the intake manifold.
If you have an upright / stock-style radiator, with the inlet on top toward the middle of the radiator, choose the "upright" option. This will add an adapter hose kit that cleanly routes the coolant to the radiator inlet. Note that you'll still use the included upper radiator hose, you'll just add the adapter hose kit to the standard hose. If you have a crossflow radiator, with the inlet all the way on the side of the radiator, choose "crossflow", as you don't need the adapter hose kit.
Why does the 1994 and the 2001-2005 (NB2) need the upright radiator kit, even if you have a crossflow radiator? For the 1994 (and only the 1994), it has a goofy linkage on the throttle body that will interfere with the radiator hose unless you use the upright radiator adapter. For the NB2, there are AC lines in the way - it works without the adapter, but it's clumsy and could be better. In both cases, with the adapter, it fits well.
If you are going to be using this reroute with a turbo, our turbo connection kit includes new multi-layer silicone lines with heat shielding, anchors and all fittings. This kit works great with our turbo kits (with our Garrett turbos), as well as Mazdaspeed Miata IHI turbos (on an MSM block or a non-MSM).
If you don't already have banjo fittings (hose barbs) on your turbo - e.g., you have our old hard line kit - add the banjo fittings above. Note that clicking the box will only add one, you need two. Please be sure to edit your cart. Most people will already have banjo fittings and won't need more.
Built in the US. Includes everything required for installation. Compatible with stock and FM turbo EGR piping. Compatible with both upright and crossflow radiators. Compatible with our Big Spark kit. Includes all required hoses/lines, custom thermostat gasket, and fittings as well as plates to block off either the thermostat or the thermostat neck (at the head) and plugs for unused fittings.
There's a bunch of noise about reroutes and 01-05 head gaskets, thanks to that head gasket having different size passages to manage the coolant flow better with the stock routing. Are they safe? Do you have to use an earlier head gasket? In short, you'll be fine with the stock headgasket - we've had this reroute on our development '02 through thousands of street and track miles with no issues, and we're not the only ones. If you have to swap the head gasket for other reasons, you might as well use the earlier head gasket, but it's not a requirement.