Radiator Cap

    
Radiator Cap is specially crafted model of radiator like a badge, located on the front center portion.

The radiator cap is a very important part of a vehicle's cooling system, yet it is often overlooked when troubleshooting overheating or coolant loss problems. Consider the radiator cap's fourfold job:

1. It's the filler cap through which coolant is added to the cooling system. Although the cap does not have to be removed to check the coolant level inside the radiator on most passenger cars and light trucks today (that's done by simply checking the level in the coolant reservoir), it must come off when the coolant is changed (every 2 years is recommended).

The "earless" caps that are original equipment on many vehicles can be very difficult to remove. That's why Stant makes a unique easy-grip, Swiv-el® cap. The cap is designed so its internal parts swivel as the shell is turned, making the cap much, easier to install and remove.

2. It raises the boiling point of the coolant to prevent overheating and coolant loss. Pressurizing the cooling system raises the boiling point of the coolant the same as a pressure cooker raises the boiling temperature of water.

A 50/50 mixture of ethylene glycol antifreeze and water normally boils at 227 degrees F.; with 4 lbs. of cap pressure, the boiling point goes up to 239 degrees F.; with 7 lbs. of pressure it rises to 248 degrees F.; and with 14 lbs. of pressure it is increased to 263 degrees F.

3. It's a pressure relief valve that prevents a dangerous buildup of internal pressure within the cooling system. When an engine is shut off, a heat soak period follows during which pressure can build within the cooling system. The cap vents this pressure by allowing a small amount of coolant to overflow the radiator into the coolant reservoir. This prevents damage to the engine and the more vulnerable cooling system components such as the radiator, heater core, hoses and water pump seal, while preventing the loss of coolant that escapes from the radiator.

4. It's also a vacuum relief/siphon valve. As the engine cools, the coolant inside the radiator and engine, along with any vapor pockets that may have formed, begins to contract. This creates a vacuum within the cooling system. The vacuum relief function of the cap allows coolant to be siphoned from the reservoir back into the radiator to maintain the proper coolant level.