How Long Can You Run an Engine without Coolant?

• If you are talking about an internal combustion engine, then the time period can vary, depending on the size of the engine and other factors like fuel quality and coolant flow rate. 
• If the cooling system fails, an engine will overheat and damage itself.
• The Coolant takes the heat from the engine and get cooled in the radiator, this cooled coolant again circulates around the engine and repeat the process.
• Usually coolant is mixed in the water with 1:1 ratio.
• If u does not provide coolant the water gets overheated with in a short period of engine run. Water gets heated less than 10-20 min (Depending upon the engine C.C), when this heated water circulates around the engine, the engine gets over heated and may cause damage to gasket, piston rings, and many of the parts inside the engine.
• There are two most common types of engines are air-cooled and water-cooled.
• Air-cooled:
• This engines do not require any cooling system, but they have some limitations because of the fact that there is no radiator. This means that if you run your engine without any coolant, this engine comes under smaller C.C or Smaller in Horse Power, ex: bike engines.
• Water-cooled:
• Water-cooled engines use a radiator to cool the oil in the engine's cylinders which prevents overheating. 
• If you run water-cooled engines even for a smaller time the engine will overheat and cause damage to the bearings or pistons. 
• The engine will start to overheat and could cause damage to your engine parts. This is because most engines are built with metal cylinders, which have fins on them to direct heat away from the cylinder walls. If there is no coolant running through these fins, then it cannot dissipate all of the heat produced by the burning fuel and so it causes overheating.
• After that time, the head gasket will get extremely hot. At this point, you should stop the engine immediately and let it cool down to room temperature. This is because if you leave the engine running after its cooling period has expired, the combustion chamber could ignite.
• Without proper cooling, the pistons and cylinders could start sticking due to thermal expansion. Overheating causes cylinder head gasket failure which results in power loss, overheating of oil, and possibly even total engine failure if a piston hits the cylinder wall while running hot.