Mishimoto® (16-23) MX-5 Miata Windshield Washer Reservoir Tank

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Compatible: (2.0L)

2016 - 2023 Mazda MX-5 Miata


This tank eliminates the factory low-level warning sensor



Simplify, then add washer fluid. That’s how the saying goes, right? Add even more lightness and style to your already-lightweight and stylish roadster with the Mishimoto Washer Fluid Reservoir for the 2016+ Mazda Miata ND.

Replace your heavy, unsightly plastic reservoir and leaking stock cap with this beautiful, all-aluminum TIG-welded tank designed to save your car some weight – and it won’t leak a drop, thanks to our specially-designed venting system. Engineered right here in Delaware, we designed this tank not only to look great, but specifically to reduce washer fluid capacity by .75 gallons, saving you 6 pounds compared to the stock unit when full. You could go on a diet and exercise every day for the next month, or pick up this tank instead and save just as much weight on the track without foregoing those steak dinners you love so much. Your call.

Available in a chic polished aluminum shine or a matte black powder coated finish for a more understated look, this tank ships with the Mishimoto Lifetime Warranty so your windshield will always be just as shiny as those autocross trophies.

  • Direct-fit for the 2016+ Mazda Miata
  • Durable, lightweight, fully tig-welded aluminum
  • Aluminum construction is more resistant to discoloration and cracking than stock plastic tank
  • Reduces washer fluid capacity by 0.75 gallons, therefore reducing total filled weight
  • Filled reservoir is 6 lbs lighter than filled stock tank
  • Special ventilation system ensures no fluid leaks
  • Includes black Mishimoto fill cap
  • Available in polished or black powder coat
  • Installs in under 30 minutes
  • Mishimoto Lifetime Warranty



FITS 2016+ Mazda Miata


CAPACITY 0.25 gallons
MATERIAL 6061 Aluminum



(1) Aluminum washer tank
(1) Mishimoto black fill cap
(1) Weather strip
(1) Mishimoto Lifetime Warranty



At Mishimoto, we know how passionate the enthusiast community is about the fact that Miata Is Always The Answer, and we share that passion!

But by the same logic, we also feel strongly that Washer-fluid Always Sloshes Heavily Everywhere, Rendering FR-layout Legends Unnecessarily In-Direct. Always up for a way to improve on an already wonderful car, we are here to change that by bringing you a 2016+ ND Miata windshield washer fluid reservoir that embodies the true spirit of the car not only by being attractive, but also by shaving some pounds and adding some lightness (if I may borrow the expression from another famed light-weight roadster enthusiast).

I’ve found most weight-loss programs to be a bit over the top and borderline pseudoscientific, but at Mishimoto, we’ve adopted a three-step plan that works very well for us.

Here’s a photo of the stock tank that we will be replacing:


Step 1: Make it lightweight

I feel like I barely even need to elaborate on this to a group of Miata owners; I once met a Miata driver who told me that his primary dieting motivation was improved autocross times. It is important for Miata parts to be lightweight, and every little bit counts, so we’ve cut the size of the reservoir roughly in half to keep those kilos off. Our tank holds .75 gallons less fluid than stock, saving a grand total of 6lbs when full of washer fluid – this way, you can scrub weight but also have a nice, clear windshield.


To put that in perspective, three of my coworkers had Chipotle burritos for lunch yesterday (clearly, not avid autocrossers), and from their delicious eating experience, a new unit of measurement was born: 3 burritos at 4.56lbs, or 1 Mishilunch. All told, we are helping your Miata shed 1.32 Mishilunches of weight. That’s just about four burritos, and that’s with guacamole, thank you very much.

One Mishilunch
One Mishilunch

Our first step was to whip together a model of our miata parts on the computer. Steve, the project engineer, accomplished this one in Solidworks.


Next, with the dimensions of the tank sorted out, we measured out the components and fabricated a prototype to test the fitment.

Cutting some sheet metal!
Cutting some sheet metal!
All mocked up and testing the fitment.
All mocked up and testing the fitment.

Step 2: Make it pretty

As with most under-hood modification, function and form are both important parts of the equation. Steve has done what he could to make this thing look awesome. He ensured that the angle of the aluminum on the top of the tank closely matched the angle of the strut tower, and this really helped a lot to bring that part of the bay together to comprise a sharp, cohesive aesthetic. After making several changes to the original design to guarantee fitment to the highest standard, it was time to create a prototype. Have a look at some installed shots, below.

The Mishimoto tank, viewed from the driver's side of the engine bay.
The Mishimoto windshield washer tank, viewed from the driver’s side of the engine bay.
Here's the tank from the front. Notice how the tank continues the lines in the design of the strut tower.
Here’s the washer fluid tank from the front. Notice how the tank continues the lines in the design of the strut tower.
And from the passenger side - you could split hairs with this thing!
And from the passenger side – you could split hairs with this thing!

Here’s one more shot of the tank in black.


Step 3: Give me a discount on these Miata Parts!

I’ll do one better: not only we are holding a discounted pre-sale for this tank, but that pre-sale actually begins right now. For a limited time, take advantage of this forum members-only discount to pick up one of these for your ND Miata. This windshield washer tank is available in the polished finish pictured or in a black powdercoat finish for a more understated, refined appearance.



One of the major benefits of sharing our R&D process among enthusiast communities is the opportunity to learn even more about what we can do to make the best possible product. Once I revealed our reservoir to the forums, I was quickly made aware that there is an annoying flaw with the stock tank: a leaking cap!

Preparing our new solution for testing
Preparing our new solution for testing

We want to ensure that our products provide as much benefit as possible to our customers and your beloved vehicles, so when we realized this pesky problem was so important to the community, we brought the tank back to the drawing board to make sure we fully satisfy your needs. In fact, we’ve already got our solution figured out! But before I explain it, let’s take a quick look at the problem.

The Affliction

Some of you employed very colorful Smurf-related imagery in describing this problem – one that’s quite evident with only a quick glance under the hood. Washer fluid. EVERYWHERE. And for those of us in colder climates that require anti-freeze, it’s BLUE! It looks like a Smurf… well, I’ll leave that to the forums.

Picture property of BigBoyND, a member of Miata.net who graciously allowed us to use his photo.
Special thanks to BigBoyND, a member of Miata.net who graciously allowed us to use his photo

So, what exactly is going on here, and how can we mitigate it?

The Diagnosis

The root cause of blue splatter under your hood pertains to the physics of fluid transfer – that’s right people, science is the problem here, but science is also the solution (if only that were more apparent to some folks!). But we’ll get to that in a second.

Let’s imagine a scenario: You’re lapping around Lime Rock on an open track day and gaining fast on a local insect who, though he’s on track to set his personal record, fails to yield to quicker traffic. SPLAT. So, you press a button to cue the nozzles and wipe Mr. Ayrton Se-gnat off your windshield.

When you activate the windshield sprayer, a pump near your reservoir expels washer fluid to your nozzles, displacing fluid from the tank and creating a vacuum condition within. Left uncorrected, this causes your fluid pump, which would have to fight against the low-pressure draw inside the tank, to work overtime. Eventually, something would have to give – the pump motor, a seal, etc. Pumps don’t like to work overtime, and if you try to ask them to, they will often quit on the spot! Damn unions.

To keep the tank’s internal pressure on par with the atmospheric pressure outside the tank, a small slit is incorporated into the stock cap, allowing air to enter the tank and equalize pressure as fluid leaves to be squirted on to your windshield.

However, that slit is also the source of our aesthetic woes. It lets air in, but it also lets rebellious washer fluid out.

The Prognosis

Even though our reservoir is aluminum and snazzy-looking, it is not exempt from also requiring pressure equalization. We initially accomplished this with a small hole on the top corner on the back of the tank.

miata tank cap leaking
The equalization hole in the Mishimoto reservoir

Science-y pressure problem: Solved.

Aesthetic fluid problem: Solved…sorta?

Our tank would likely still have leaked on the back, which may or may not have been visible. But given how annoying this leaking cap can be, we wanted to actually SOLVE the problem – not just move it to the back where you can’t see it.

So, we’ve decided to go the extra mile and do better than taking the easy way out with a band-aid solution. And how did we do that?

Well, we used a different kind of “band-aid solution”.

Our solution to the leaking tank problem
Our solution to the leaking tank problem

The Cure (the band-aid, not the band)

What if there was a material that is permeable to air but impermeable to water? As it turns out, there is, and it comes packaged as a handy little sticker that happens to be the perfect size for covering up our equalization hole. See? Re-defining the “band-aid solution”.

But we wanted to ensure that the performance and flow of this membrane was adequate to equalize the tank without being overly taxing on the pump motor. The stock cap’s slit is highly restrictive, so we knew that the motor would most likely be able to handle just about anything we threw at it (our EQ hole is much larger than the stock slit). But, just to be sure, Steve ran it through its paces with some testing.

First, Steve mounted the reservoir in a vice at his workstation.

leaking washer fluid

We paid our friends at the local Mazda dealership a visit to pick up a washer fluid pump. Once we had that in hand, Steve mounted that in its appropriate location on the tank.

leaking tank fix miata

With the pump in place, Steve secured a line from the pump to a glass beaker. The line was taped to the receptacle to prevent any unwanted splashing.

miata washer fluid leak

After placing the beaker above the water level in the tank, Steve connected a power supply to the pump – this would ensure that we could hold the pump at a steady state using constant voltage. Essentially, we were going to prevent the pump from overworking itself, and this would allow us to measure the volume of fluid pumped in a specific amount of time, all else equal.

miata tank washer fluid cap spill

With this information, it would be easy to determine whether the equalization would be adequate even with our new filter in place. Well, consider this problem solved! As I mentioned initially, we were very confident in this design because the slit in the stock tank is so restrictive, and the pump was designed to work under those conditions.

Here’s the mad scientist himself, carefully evaluating his experiment.

washer fluid leaking miata

Pre-Sale and Release

Next will be product release! As we speak, we are implementing this change in all our existing inventory, and any reservoir shipped from this point forward will include this filter. For those of you who have already received a tank, we will supply you with a kit to retrofit your tank at home.

Thanks for following along, and a special thanks to all of you and your feedback that led to a better product!


Install Guide: