Most of us who own cars in India would have faced this problem of a failed Engine start when ever we try to start the car when the Engine is already hot. This is a common problem faced by many o this happens.
The underlying reasons.
1) If your car is a gasoline driven engine , then the car would’nt start with a hot engine sometimes due to the fact that gasoline is initially mixed with the air before it goes into the cylinder. If one stops after driving the car for a long time and tries to restart, sometimes the car would”nt start because of the extreme vaporisation of the fuel , which causes a Vapor lock “. This Vapour lock obstructs the normal fuel mixture inflow to the cylinder. Most often the Engine would therefore restart once it cools down as the Vapour lock would cease after cooling.Of course most of the older gasoline engines had this problem but the new cars are equipped with better electronic injection systems to circumvent this vapor lock.
2)If your car is a Diesel car, then it is rare that you could have a starting problem because of a vapour lock but it is sometimes quite possible that the car might not start once you switched it off after a long drive suddenly. The reason could be a compromised starter system which would not work when the Engine becomes hot . If the starter system is not equipped to start at hot temperatures or If the starter itself has been damaged, then there is a high possibility that the car would not start when it is hot.it could also be that the fuel pump has become inefficent such that it is not able to pump enough fuel at hot temperatures owing to the heat .Many Indica diesel cars have this hot start problems . If the car starts properly when it is cold, then the starter might not be the issue, but the fuel pump itself could be the problem.