Water Reservoir Tank Boiling

This escaped air causes bubbling in the coolant antifreeze reservoir which can often be mistaken for boiling.

Water reservoir tank boiling.

Your local repair shop can perform test to identify cylinder head or engine block cracks. The engine cooling system is pressurized somewhere between 5 to 15 pounds per square inch. I suspect that the boiling you were seeing in the reservoir wasn t boiling at all but was actually combustion gasses being blown into the water jacket and migrating out to the reservoir where they were coming out as bubbles. It has some other useful tools and info in it.

Federal mogul radiator cap. You can experience a shot of boiling water exploding under pressure. That would indicate a blown headgasket. The increase in pressure will also increase the boiling point of the coolant.

The fact that the coolant was boiling out of the reservoir cap suggests that the thermostat may be stuck closed. Here is a handy chart if you ever need it. The reason a bad cap can allow the water to boil is because the pressure the cap is designed to keep in the cooling system makes it more difficult for the water molecules to escape as a gas. If you re seeing gas bubbles or some boiling in the liquid when you remove the radiator cap a cracked head or block may be to blame.

When the coolant is released to the reservoir it may boil because of the fact that it is at atmospheric pressure and the water portion will boil at 212. It could mean that air is somehow getting into an otherwise pressurized liquid system or it could mean that the the last time the coolant was changed some air was. In fact if you placed the coolant in a vacuum it would boil sooner. One of the most common causes is a blown head gasket in which the air pressure inside the cylinder heads is transferred to the cooling system.

Do not remove a radiator cap from a hot engine to check.