Moroso Coolant Tank

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Moroso Coolant Tank

Engine Coolant Recovery Tank - Expansion Tank

What does the Engine Coolant Tank do? 


The coolant recovery tank is a reservoir designed to collect hot coolant; from the radiator as the coolant expands. Your engine's coolant recovery tank is sometimes rightly called the expansion bottle. This is because when the engine cooling system is cold, The water/coolant volume has contracted, and volume is low. But, as the engine cools down, the coolant in the radiator contracts, creating a vacuum in the radiator.

As a result, this vacuum draws coolant back into the radiator. So, it's packed at all times, preventing air locks.

When you run the engine, the coolant temperature rises to the designed operating temperature. The engine Coolant volume also increases as the coolant liquid expands. That heating and expansion process builds pressure in the cooling system, which the radiator pressure cap/regulator regulates. It's held at around 0.9 to 1.2 bars +/-. This above atmosphere pressure saves a critical function. It raises the boiling point of water to way above 100°C. You do not want the engine's coolant to boil and create air pockets in the system that will create hot spots. Hot spots will cause temperature differences that cause the cylinder head to warp or crack. 


These terms also refer to the Coolant Tank:

  • Coolant recovery tank
  • Expansion tank
  • Recovery Tank
  • Overflow Tank
  • Coolant Recovery Bottle
  • Coolant Recovery Tank
  • Pressurized Recovery Tank

How a Coolant Tanks works. 

When you top up your engine's coolant system with antifreeze coolant, you fill the radiator up to the neck, and the recovery tank up to the maximum indicated. The max level leaves much space in the tank for a purpose.

When running the engine hot, the coolant expands, and pressure rises. At the rated pressure (according to the radiator cap), the water forces the radiator cap valve open and escapes into the coolant recovery tank. As a result, the coolant level in the recovery tank rises above the max mark.

When you park the vehicle, the coolant temperature drops, and the volume reduces as the coolant contracts. The vacuum in the radiator opens a smaller valve, and coolant flows back into the recovery tank. Atmospheric pressure in the recovery tank forces coolant into the radiator, whose pressure is now below atmospheric due to contraction of coolant.

Another function of the coolant recovery tank is to remove air bubbles from the cooling system. Coolant without air bubbles is much more efficient than coolant with air bubbles. So an engine without a recovery tank, the air is sucked into the radiator instead of coolant. As a result, it is causing air locks and the formation of rust. When rust forms inside the cooling system, you must flush out the design and replace the coolant. One reasonably common sign is an overheating engine even though the coolant tank contains an average coolant level.

Traditional radiators use a radiator cap that holds pressure; until it reaches its preset pressure threshold. Once the cooling system pressure exceeds the cap rating, the cap releases coolant until the pressure falls. In older vehicles, the excess coolant was dumped onto the ground without a coolant recovery tank. So, the next time the engine starts with cold coolant, the coolant level in the radiator is low. The remaining coolant would expand to fill the entire radiator; once the engine warmed up again.

To keep the radiator full at all times, car makers developed a new radiator cap and installed a tank. The radiator cap operates like; the older versions to open and bleed off excess coolant. But, instead of expelling the coolant onto the ground, the coolant drained into a recovery bottle/tank. So far, the cap operates just like the previous caps. However, as the engine cools and the coolant contracts, it creates a vacuum inside the radiator.

A venting mechanism in the cap allows the vacuum to draw coolant; back into the radiator from the recovery tank. The recovery tank in these vehicles is simply storage containers. So they are not under pressure at any time.

So, using a coolant recovery tank prevents; a slightly overfilled radiator system from venting onto the ground. Also, using an expansion tank; with a conventional radiator adds additional coolant capacity to the system to improve system performance.

The Moroso Performance Products Coolant Tanks are MADE IN THE USA!