I think the radiator is block somewhere, and so the coolant is not circulating resulting to the overflow,check whether the coolant overflows through the radiator overflow tube too.
Bro these are indications check soon with some workshop,do not let overheat the engine and blow the gasket and damage the engine.
Good luck.
As said by Alexddas, check the radiator for any blockage. BTW, was the temperature needle going towards H mark when the reservoir was overflowing.
If the temperature needle was ok, then you can check the cooling system by filling the reservoir below LOW mark and driving for few Kms. If it overflows again get the radiator flushed.
Also check the radiator cap.
Reservoir tank is not overflowing fully. Reservoir tank level is now between low and high level marks. If the reservoir level is kept below low mark, it doesn't overflow.
Temperature needle stays at 1/3 mark without moving.
Check the condition of the radiator cap.Change it if you have not already.
Could be air in the cooling system.
Park the car on a level surface, remove the radiator cap and turn on the engine.Let the engine idle and keep an eye on the coolant in the radiator.Once it begins to flow out of the radiator, put the radiator cap back on and then turn off the engine.
Also make the hole in the overflow tank cap a little big.Not too big as to allow debris to fall in.
Reservoir tank is not overflowing fully. Reservoir tank level is now between low and high level marks. If the reservoir level is kept below low mark, it doesn't overflow.
Temperature needle stays at 1/3 mark without moving.
There was a rubber seal fixed to overflow tank cap. The rubber seal has blocked the small hole on the overflow tank cap. I made the small hole little bigger and everything seems to be ok now.
Check the condition of the radiator cap.Change it if you have not already.
Could be air in the cooling system.
Park the car on a level surface, remove the radiator cap and turn on the engine.Let the engine idle and keep an eye on the coolant in the radiator.Once it begins to flow out of the radiator, put the radiator cap back on and then turn off the engine.
Also make the hole in the overflow tank cap a little big.Not too big as to allow debris to fall in.