Why water coolant leaking from water jacket - 2002 Lexus ES 300

Very often the cause of coolant being expelled from the reservoir is due to a faulty head gasket leaking compression air into the water jackets. When the engine stops circulating the coolant, with the water pump, the bubbles collect together in the radiator as they rise to the top. Then the hot compressed air passes through the pressure relief valve (often radiator cap) and enters the reservoir, thereby blowing coolant out of the overflow tube.

The water jacket is just a name for the coolant inside the engine. It is the metal of the block surrounding the coolant.


The photo shows an engine block. The 4 bigger holes are - obviously- where the pistons fit. The smaller holes lead into the water jacket'. The coolant is held between the outer wall of the engine block and the inner wall. This area between them is known as the 'water jacket'.

The coolant circulates through the water jacket and into the radiator via the top radiator hose. As it cools it goes downwards in the radiator and then back into the engine block via the bottom radiator hose

Bad Water jackets

eventually yes. with bad results. in the mean time keep topping up your radiator with coolant. not just water as this can corrode the water jacket inside the engine and restrict coolant flow. i would replace the radiator soon as.

Sound like a head gasket is leaking. The coolant is leaking from the water jacket through the failed gasket in to the engine crankcase. The "blow back" is caused by the combustion inside the cylinder to leak into the water jacket, pressurizing it.
Drain the oil immediately and do not attempt to run the engine until you have the gasket replaced. Water in the oil will destroy the engine beyond repair.

could be water pump. Check weep hole on water pump body to see if its dripping. if it is, then your pump seals are bad. Now, if coolant is leaking from engine, it could be from water jackets or engine drain plug. this all depends on where you're seeing coolant leaking from. Also, if it's not registering as hot, you might want to look at the coolant temperature sensor.

replace your radiator cap.

from what you describe I am sure it is the water pump that is leaking, check the pump bearing for play to confirm

Cars generally overhead when engine coolant is below acceptable levels. That can be caused from leakage, blockage or equipment malfunction.

• Inspect coolant level in the vehicle's reservoir or radiator.
• Inspect radiator and heater hoses for cracking causing leaking.
• Inspect the radiator for leaking.
• Inspect the inside of radiator for smudge build-up, a sure sign that the water jackets might be restricted.
• Inspect water pump for leaking or broken belt (serpentine belt)
• Check to ensure water pump properly functioning, does the pump's pulley turn?

Repair or replace any faulty item.

are u getting any white smoke from the exhaust? it could be a water jacket leaking which means it wouldnt neccessarily show up in the oil.