Fortunately I have never, in all my years of motoring, had a problem with a blown head gasket.
Could some one explain to me please what happens to cause head gasket to be blown and then starts to leak water into the engine. This is just out of interest to further my knowledge about cars a little bit more
Corrosion, a bad gasket, a warped cylinder head such as from overheating the engine, a lack of coolant for whatever reason (such as a poorly torqued hose clip, or rotted rubber hose), incorrectly torqued down cylinder head after a rebuild, a dirty jointing face after a rebuild…I’m sure folks will be able to come up with some more.
Usually corrosion if the engine was assembled correctly. Despite regular dealer service every 9,000 miles and regular coolant changes my old Astra developed a leak between no4 cylinder and water jacket at nine years and 175,000 miles - sudden overheat and white smoke out of exhaust in a traffic jam. When I changed it I was surprised at how narrow that bit was, and yes it was corroded. That took a day to fix and since the head was off new cam-belt, water-pump, tensioner, idlers, cam-cover filter, oil and filter, antifreeze, several gaskets, RTV silicone, etc.
Many years before that my Kent engine also popped a head gasket after about a year, again with the white smoke and also in a traffic jam, but that was because it turned out that I’d not fitted the best type when I built the engine (bad advice), and it was not torqued to the correct values and the engine was very high compression. My fault for being in a hurry to finish the build and not waiting for the big torque wrench to be repaired. That took an hour to fix, head and thermostat gaskets and antifreeze.
The other main reason is being mean with the antifreeze and allowing frost damage.