The cooling systems hold different amounts of pressure, but typically sit somewhere between 13 and 16 pounds of pressure per square inch (PSI). This pressure is controlled by the radiator cap and needs to remain constant.

Signs of a Faulty Radiator Cap

Leaking Coolant. If the radiator cap is stuck, pressure may build inside of the radiator, which could cause cooling system components to leak or burst. If you notice coolant near the radiator or the radiator cap, then you clearly have leaky coolant. Check to see if the radiator has holes in it or if the cap looks worn or damaged. If so, then replace the cap.

White Streaks on Radiator

When coolant leaks out of the radiator filler neck and dries, it often leaves white streaks behind. While you may not notice coolant leaking from under the radiator cap, look out for these white streaks. We may tell you the cap is leaking under pressure or intermittently.

Overflowing Reservoir

Coolant goes into the reservoir tank as it expands. The radiator cap releases the extra pressure by sending some coolant into the overflow tank. If you have a bad radiator cap, the coolant could get released too quickly and cause the reservoir to overflow. While you’re in there, check to make sure your coolant overflow tank is working properly.

Radiator Hose Collapses

You may have a bad radiator cap if the radiator hose collapses. The vacuum won’t be released by the radiator cap properly and it will cause the radiator hose to collapse during the cooling down period. If this happens, inspect the cap to see if there is any damage. If there is, replace it immediately.

Radiator Hose Bursts

If pressure in the cooling system is too high, you are likely to see one or more hoses start to spray coolant all over the engine bay. Most of the time the pressure isn’t high enough to rip the hose in half. You will often see a pinpoint leak that only sprays coolant when the car is warmed up. A hose with a small hole may actually seal just fine when the car is cold. As you drive, pressure in the cooling system will build. The pressure will eventually be enough to force coolant through the tiny hole and your car will slowly lose coolant.

Overheated Engine.

Leaky coolant or air in the cooling system can lead to an overheated engine. If you notice your engine starting to steam from getting too hot, don’t look under the hood unless you’ve turned the engine off. Then, let the engine cool for some time before popping the hood. That way, the engine can remain cool as you check it out. If there is coolant fluid near the radiator cap, there could be damage to the pressure cap. Check for that and replace as needed.

Air Inside the Cooling System

When your radiator cap does not seal properly, air could make its way inside of the cooling system. This will cause air pockets to get inside of the heater core, thermostat, and radiator hoses. As a result, the engine will start to overheat