Surge tank

Imagine you have a water bottle that you are slowly drinking from throughout the day. As you drink from the bottle, the water level inside the bottle drops. But, there is a problem - your drinking straw is not long enough to reach the bottom of the bottle. This means that as you keep drinking, the straw will eventually start sucking air instead of water because there won't be enough water left in the bottle. This is similar to what happens in a car engine's cooling system.

A surge tank is like a little helper that sits in the engine's cooling system to fix the problem we just talked about. Its job is to make sure that the engine always has enough coolant (a special liquid that helps keep the engine cool) circulating through it. The surge tank does this by being the first place the coolant goes after it leaves the engine block. So, when the engine is running and it needs coolant, the surge tank is like a backup supply that sends extra coolant back down to the engine to ensure it always has enough.

Think of it like a gas station for your engine - it's always there and ensures your engine doesn't run out of juice (in this case, coolant).