Blown Head Gaskets can cause overheating - or they are the effect of another issue that made the engine overheat causing the cylinder head to warp as was the case of this Toyota 2.0 AZ-FE. a coolant loss in the radiator left the cooling system too low to cool the engine sufficiently. Head gaskets are thin and made of layers of substances to seal the top portion of the engine (cylinder head) to the block to keep combustion gasses contained in the cylinders and coolant in the cooling jackets and oil in the oil passages and drain backs. Symptoms of blown head gaskets are numerous. Overheating in short periods of time is the most common. Usually accompanied with rough running on one or more cylinders on cold starts up because of antifreeze in the combustion chamber but not on this RAV4. It ran great. Coolant in the oil making the oil look like a chocolate milkshake, oil in the coolant with oil on top of the coolant reservoir. Or a combination of all of them. This engine had good compression and ran well. When disassembled the head was warped more than .008" of an inch and the block about .003" - .004 is maximum for both. We had .011" total. Not only did the head need to be straightened but also needed a valve job so a rebuilt head was ordered. We believe the engine integrity was not compromised by thermal damage and are going to repair it. I put this video together for instructional information purposes because of the uniqueness of the symptoms, foaming coolant with gasoline bubbles. The only symptom was overheating on this engine.