Let’s talk about one of Mazda’s more questionable decisions with the NC MX5: the coolant expansion tank placement.
Now, Mazda got a lot right with this car. The chassis is brilliant. The weight distribution is spot on. The driving experience is exactly what a lightweight roadster should be. But then someone in the design department looked at the cooling system and thought, “you know what would be great? If we stuck the expansion tank directly in front of the radiator.”
No, really. They did that.
The Problem That’s Been Cooking Since 2006
Pop the bonnet on a stock NC and have a look at where the expansion tank lives. It’s sitting right there, front and centre, like it’s trying to photo bomb your radiator. Blocking airflow. Making your cooling system work harder than it needs to. Generally being in the way of the one thing that’s supposed to keep your engine from turning into an expensive paperweight.
It’s not terrible if you’re just pottering around town on a cool day. But the moment you start driving the car how it was meant to be driven, spirited back roads, track days, even just a proper motorway blast in summer, that marginal cooling starts becoming a real problem.
And don’t even get me started on trying to bleed the cooling system. The tank’s positioned so low that getting air out feels like defusing a bomb while wearing oven mitts. You end up doing the whole “squeeze the hoses, burp it, check the level, squeeze again” dance for what feels like hours, all while hoping you’ve actually got all the air out and won’t be watching your temperature gauge climb on the way home.
Why This Matters More Than You Think
If you’re staying naturally aspirated:
Even on a stock NC, cooling can get marginal on track or during spirited summer drives. That expansion tank blocking your radiator isn’t doing you any favors. You might not be overheating yet, but you’re not exactly operating with much margin for error either.
Relocating the tank means your radiator can actually breathe. More airflow = cooler temps = more consistent performance. It’s not going to transform your car, but it’s one less thing to worry about when you’re pushing on.
If you’re planning forced induction:
This isn’t optional anymore, it’s essential. Turbos make heat. Lots of it. Your cooling system is already working overtime trying to manage intake temps, oil temps, and coolant temps all at once. The last thing you need is an expansion tank playing goalie with your radiator’s airflow.
Every turbo NC we’ve built gets this mod early on. Not because it’s flashy or adds power, but because it’s the difference between a car that stays cool under boost and one that heat soaks after two hard pulls.
If you actually maintain your car:
Here’s something nobody talks about: when was the last time you checked your coolant level? Be honest. If the answer is “I don’t remember,” you’re not alone. Half the reason people don’t check is because it’s a faff to get to and bleeding the system after a top-up is genuinely annoying.
Relocate the tank higher up in the engine bay and suddenly it’s actually easy to check. You can see it. You can reach it. You might even check it occasionally instead of waiting until your temperature warning light comes on.
What Our Kit Actually Does
We move the expansion tank from “directly in front of the radiator like a muppet” to “corner of the engine bay where it should’ve been from day one.”
Higher up. Out of the way. Easy to access. And suddenly your radiator can do its job without an expansion tank blocking half the airflow.
What you get:
New Expansion Tank properly designed, not a bodge job.
Extended Coolant Hoses the right length, not “just long enough if you really stretch it”.
All necessary fittings because nobody wants to make three trips to the parts shop mid-install.
What you need to do:
This isn’t a 20-minute job, but it’s not rocket science either. If you can swap an air filter without googling “how to open bonnet,” you can fit this kit. You’ll need basic hand tools, a couple of hours, and the ability to follow instructions that don’t involve interpretive dance.
Drain the coolant, unbolt the old tank, mount the expansion tank, connect the hoses, refill, bleed. Job done.
The Bit Where Your Engine Bay Looks Better Too
Look, we’re not going to pretend this is why you buy it. You buy it because your cooling system needs to actually work properly. But once it’s fitted, your engine bay does look significantly cleaner.
The radiator isn’t hidden behind a big white plastic tank anymore. Everything’s neater. More organized. Less “Mazda ran out of space and just stuck it wherever.” More “someone actually thought about this.”
If you’re the sort of person who cares about engine bay aesthetics (and if you’ve read this far, you probably are), it’s a nice bonus. The car works better and looks better under the bonnet. Win-win.
When You Should Actually Do This
Do it now if:
- You’re building a turbo NC and want to do things properly from the start
- You’ve noticed cooling getting marginal on track days or spirited drives
- You’re planning any engine bay work and want to sort this while everything’s accessible
- You’re tired of wrestling with the cooling system every time you need to top it up
Maybe hold off if:
- You’re genuinely never pushing the car hard and cooling is fine
- You’re selling the car soon and can’t be bothered
- You’ve got more urgent issues to fix first (like actual mechanical problems)
This isn’t a critical “your car will explode without it” mod. It’s a “your car will work better and you’ll be glad you did it” mod. There’s a difference.
The Honest Truth
Relocating the coolant expansion tank isn’t going to make your NC faster. It won’t add power. Your mates probably won’t notice unless they’re proper nerds who actually look at engine bays.
But it will make your cooling system work like it should’ve from the factory. It’ll make maintenance less of a faff. And if you’re building the car for performance—whether that’s track days, turbo builds, or just spirited weekend drives—it’s one less thing you’ll have to compromise on later.
It’s the sort of mod that doesn’t make headlines but makes everything else work better. And sometimes that’s what actually matters when you’re building a car properly instead of just chasing Instagram likes.
What Else We Do at Tracktuned
We specialize in NC MX5 builds that actually make sense. From essential prep work like this coolant tank relocation to full BMW gearbox swaps and turbo conversions. Everything we make is designed by people who build cars, not just sell parts.
Most of our products exist because we needed them for our own builds and couldn’t find anything decent on the market. No off-the-shelf nonsense that “sort of fits if you persuade it.” Just proper solutions that work.
Check out our other NC prep essentials: Alternator Relocation Kit and Compact Clutch Master Cylinder Kit.
Ready to sort your cooling system properly?