Coolant Overflow Tanks & Expansion Catch Cans

What a Coolant Overflow Tank Does

A coolant overflow tank holds coolant that expands out of your radiator as it heats up, then returns it as the engine cools. It's a non-pressurized tank, so the pressure cap sits on the radiator. When pressure climbs past the cap's rating, coolant flows through the cap and into the tank.

As the engine cools, the radiator pulls that coolant back in, which keeps the core full and helps keep air out of the system. That's why the tank and cap work as a pair, so check your radiator caps when you replace a tank. A worn seal or weak spring can let coolant leave early or keep it from returning.

A system that can't hold its coolant level can also lead to a P2181 cooling system performance code on later-model vehicles. When you're ready to finish the job, shop JEGS radiators and radiator components for tanks, hoses, and hardware.

Overflow Tank vs. Coolant Expansion Tank

An overflow tank only stores extra coolant, while a coolant expansion tank is pressurized and part of the circulating system. On an expansion tank, also called a degas bottle, the pressure cap sits on the tank itself. Coolant circulates through it whenever the engine runs.

An overflow tank, often called a coolant recovery tank, sits outside that loop. It only receives coolant through the radiator cap and sends it back as the engine cools. Because the two designs handle pressure differently, you can't swap one for the other without changing where the cap lives.

Start by finding your factory pressure cap. If it's on the radiator, you need an overflow tank, and if it's on the reservoir, you need a pressurized expansion tank. Dorman Products offers both types, including a heavy-duty pressurized reservoir for 2001-2011 Freightliner trucks and a non-pressurized reservoir for 1984-1988 Toyota models.

For a custom aluminum upgrade, Mishimoto offers an aluminum coolant expansion tank.

Coolant Overflow Tank Materials and Styles

Most coolant overflow tanks here are aluminum or plastic, and your pick comes down to finish, mounting space, and how you want coolant handled. Aluminum tanks come in polished, powder-coated, and anodized finishes for a clean engine bay. Plastic tanks are a simple, functional choice.

Here are examples of the sizes and styles you'll find:

• Champion Cooling Systems radiator overflow tank, 2 in. D x 13 in. L, polished or black powder-coated
• Proform billet aluminum radiator overflow canisters, 6-3/4" tall x 3" diameter, anodized black
• Allstar Performance plastic non-recovery overflow tank with a drain
• Canton Racing Products coolant recovery tanks in 8-1/2" x 7" x 4" and 8" x 5" x 4" sizes

Measure your mounting area before you order, since tall, narrow canisters and box-style tanks fit very different spaces. A non-recovery tank with a drain holds coolant until you empty it by hand.

Choosing a Universal or Direct-Fit Radiator Overflow Tank

Choose a universal radiator overflow tank for custom builds and a direct-fit reservoir when you want a factory-style replacement. Universal tanks, like the Moroso 2-quart catch/overflow/recovery tank, mount wherever you have room. Direct-fit reservoirs match the original mounting points and hose locations for a specific vehicle.

This category includes OE coolant reservoirs for select Dodge Challenger and Charger models and an overflow tank for the 2001-2007 GM 6.6L Duramax. Confirm your year, make, model, and engine before you order a direct-fit part.

For a universal tank, plan the hose route from your radiator neck and pick a spot that's easy to see and fill. If you're upgrading to one of our performance radiators, our guide to installing an aluminum radiator in a classic car covers fitment. You may also need new thermostats, housings, and hoses to finish the swap.

Transmission and Oil Catch Cans

Transmission and oil catch cans collect fluid or oil vapor that would otherwise vent onto the ground or into your intake. A transmission overflow catch can captures fluid pushed out of the transmission vent. This category includes transmission overflow catch cans and deep pan kits for GM Powerglide and TH400 automatics.

An oil catch can mounts in the PCV line and separates oil from crankcase vapor before it reaches the intake. Mishimoto also offers baffled PCV-side oil catch cans for the 2017 and newer Honda Civic Type R.

You'll also find replacement caps, hardware, and billet coolant reservoir cap covers for Corvette LT2 and Z06 applications. These parts let you refresh the pieces around your tank, and billet cap covers give the engine bay a finished look. Shop all cooling, heating, and A/C parts to complete your system.