Moroso Catch Can And Coolant Tank Keeps Miata Fueled And Cooled

It has been a while since we posted updates to our Project CrossTime Miata. But that doesn’t mean modifications, tweaking, and tuning haven’t been going on in the background. One of our recent installs was of some often overlooked components for modern engines — an air/oil separator catch can and a coolant expansion-tank reservoir.

Sure, in a casually driven sports car, you might not need to consider fancy aluminum catch cans or super-strong coolant expansion-tank reservoirs. But, as the revs go up — and stay there for sustained periods of (track) time — you want to keep both oil and coolant where they belong . . . inside the long block.

With our mission set, it was time to find the beefiest components around. So, we reached out to Moroso, who make both universal and model-specific, direct-fit aluminum air/oil separator catch cans and coolant reservoirs for most any application, including all Mazda Miata models ranging from 1990 to present. Moroso also has universal cans and tanks, so check out its website to see if they have one for your car.

The Moroso Aluminum Coolant Expansion Tank (P/N 63780) fits all NA Miatas 1990-1997. Moroso also offers applications from NB through the ND cars.

The Moroso Aluminum Air/Oil Separator Catch Can (P/N 85488) fits all Miatas from 1990 to today. The Moroso Aluminum Coolant Expansion Tank (P/N 63780) we ordered is for NA Miatas, 1990-1997. It also offers tanks for later model Miatas up to today (see chart later in this article). To see if they have a direct-fit or a universal solution for your application, check out Moroso’s website.

When these expertly crafted aluminum aftermarket pieces arrived, it was time to check out the box contents and how we would install these correctly. And most importantly, relay to our readers why we need them at all.

When these expertly crafted Moroso aluminum aftermarket pieces arrived, we emptied out the box contents and read up on how we would install them.

Ya Gotta Keep ‘Em Separated

A factory PCV system is fine for most vehicles, but pedal down with the 1.8L revving for a long time and the oil blow-by headed back to be re-burned in the intake can add up. A stock oil breather system can lead to excessive deposits in the intake and on the valves, and create vapors causing improper air/fuel mixture, which could lead to dreaded detonation.

While the plumbing differs in various models, the Miata has a common system that vents from the valve cover and re-circulates the excess back into the intake manifold to be reprocessed. An air/oil separator oil catch can is an essential part to keep any performance-oriented car running right — especially track cars — and not get fouled plugs by excess oil in the intake and cylinders. 

Adding a catch can to the existing PCV system allows for air and moderate vapor to pass through to be re-burned in the combustion chambers. But, the liquid and gunk are saved in the catch can, to be emptied later. If you wonder how it works, while on Moroso’s website ordering the parts, we found this cool video where they put a clear reservoir on the catch can to show what goes on inside the vent system.

Plumbing The Can

The Moroso kit is provided with a billet-aluminum mounting clamp, mounting hardware, as well as 3/8-inch and 1/2-inch rubber hose. Heavy-duty brass straight and 90-degree barbed inlet, outlet, and bottom drain fittings are provided, as well. Of course, if you want to make it sexier, stainless steel braided hoses and colored anodized AN fittings could be used instead.

The Moroso Air/Oil Separator Catch Can system is provided with straight and 90-degree inlet, outlet, and bottom drain fittings, along with a rubber hose.

Depending on your placement in the engine bay, you may need an additional length of hose, but the kit comes with everything you need to install it including the bracket, fittings, hardware, and hose. We used Teflon tape to keep the fittings sealed tightly.

The Moroso Air/Oil Separator Catch Can is an attractive raw aluminum unit with pretty welds and solid craftsmanship. The system has a billet aluminum mounting bracket that is made to bolt to the cowl. We had our fire-suppression lines running there, so we found a spot nearby that used to house the windshield washer reservoir, which worked perfectly.

The plumbing was simple enough, as you can see in the photos. Originally, there was a single 3/8-inch hose going from the valve cover into the intake manifold. Now, the catch can is essentially inserted between the two with the use of two hoses — one coming out of the valve cover into the can, and one coming out of the can into the intake manifold. It doesn’t get much simpler than that. Additionally, we had a perfect spot to plug a 1/2-inch hose onto the drain fitting, which we were able to route out the bottom of the car so we could easily drain it into a pan on the ground.

Installing the Moroso Air/Oil Separator is about as easy to install as you can get. Finding a secure out-of-the-way spot to mount it can be challenging in a Miata, but seeing we didn't have a windshield washer reservoir anymore, it was a perfect location. We were able to run the drain hose out the bottom to catch the oil in a pan.

Moroso Air/Oil Separator Kits

Fits: Custom and Direct-Fit Applications
• Plumbed into a vehicle’s PCV system to capture the excess crankcase vapors, residual oil mist, and moisture from re-entering the intake tract
• Vehicles from the factory vent these excess crankcase vapors, residual oil mist, and moisture right back into the intake manifold which could cause: detonation, oil deposits in the intake tract including the valves themselves, and decreased intercooler efficiency
• Increases engine performance from cleaner intake air
• Air-Oil Separators have billet aluminum bodies with internal baffling and mesh media
• Includes heavy-duty brass inlet and outlet fittings, Fuel/Emission/PCV Vapor hose, stainless steel mounting bracket and billet aluminum mounting clamp for the body of the separator
• Some vehicle crankcase-ventilation systems require that 2 Air-Oil Separator bodies be used to capture and ventilate the system adequately

Moroso Air-Oil Separators are available in 2 sizes; not all kits are available with both size body, please see Air-Oil Separator Application Chart in the Moroso catalog or on the Moroso website for more information.
AIR-OIL SEPARATOR KITS, LARGE BODY
• The original size, 43% more capacity than the Small Body version
• Features a bottom drain with elbow that makes draining the collected oil virtually mess-free
• Polished body can be chromed, painted or powdered coated for a custom look
AIR-OIL SEPARATOR KITS, SMALL BODY
• Smaller size fits in more applications, and some customers prefer the smaller size body
• Two-piece body unscrews for draining
• Available with a polished or black anodized finish

Keep Your Cool

One of the cooling system items on Project CrossTime that hasn’t been upgraded is the factory coolant expansion-tank reservoir. In the NA Miata application here, it might not have been experiencing dramatic overheating, excess pressure, or leaks. But it is old, and they are known to crack over time — and you don’t want a sudden flow of water on the front tires in a high-speed corner. The Moroso Aluminum Coolant Expansion Tank will provide an extra level of security when the car heats up on track lap after lap.

One additional item to consider is that CrossTime is used heavily for autocross. These tight, twisty, pylon circuits are high-RPM with not a lot of high-speed, straight-forward direction that is more effective for cooling systems. Also, after a run, we return straight back to the staging lanes to sit and wait on our next turn, so the car keeps building heat. As the temps go up, so does the pressure, so the expansion tank can hold coolant and air being pushed up to the radiator neck.

Moroso Coolant Expansion Tanks are a model-specific, direct-fit for most applications and bolt into the factory locations. These tanks are made from billet 6061-T6 aluminum and are held together with a high dose of weld porn.

All Moroso Coolant Expansion Tanks are a model-specific, direct-fit for most applications and bolt into the factory locations. These tanks are made from billet 6061-T6 aluminum and are held together with some gorgeous welds. The tanks are 100-percent pressure tested to avoid any flex or failure and provide a perfect location to fill or bleed off excess air for these low-mount style radiators. The Moroso Tank’s highly polished-aluminum finish really dresses up this ancient engine bay. It is also topped off with a billet aluminum five-star ‘MOROSO’ tank cap to make other factory reservoir tanks look like Fisher-Price kid’s toys.

Moroso Coolant Expansion Tanks for Mazda Miata

Model/Years Part Number
NA 1990-1997 63780
NB 1999-2005 63781
NC 2005-2015 63779
ND 2016-Present 63778

The Final Verdict

After installing these two Moroso 6061-T6 aluminum tanks in our NA, we think we might need to clean up the rest of the engine bay (hey, it’s a race car!). They are by far the prettiest parts — highly functional, but with a bunch of polished-aluminum, clear-coated flare for under the hood of the mighty Miata.  

All kidding aside, the surprising part was how well the air/oil separator works. After our first weekend at a track day, we pulled almost a half-pint of oil out of the can. As you know, oil is supposed to go UNDER the pistons, not on top of them. That would’ve been a lot of extra oil being thrown at the plugs. With 189,000 miles on this car, it makes us wonder just how bad the inside of the combustion chamber looks. We will definitely be changing the plugs before the next event, at the very least! 

(Photo credit: Jane Absalom)

These were easy installs, maybe an hour — tops. Even the novice wrencher will find it no big deal to complete. The Moroso instructions are straightforward, and everything we needed for the install is provided except for the necessary tools. No important installation notes or caveats here, just remember to ensure you use Teflon tape on the fittings, all hose clamps provided are tight, and every hose is seated correctly on the barbed fittings.

The new Moroso Coolant Expansion Tank provides us with safe storage for our radiator overflow. With the new air/oil separator, we will notice less oil in the intake, on the valves, and plugs. The result is a smoother running engine along with the more effective and efficient operation of our almost-30-year-old Miata cooling system!

Article Sources

About the author

Dave Pankew

Dave has been a gearhead forever and bought his first car at only 15. Since then he has owned, built and raced over 60 cars, turning his obsession into a career becoming Editor-in-Chief of a tuner magazine nearly 20 years ago.
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