I've Maruti 800 5-gear MPFI, Dec 2000. During the last month its getting overheated again n again. Coolant gets boiled up and rushes out with pressure from the coolant box, thus emptying the radiator. This happened during the traffic jam when I had to run the car on 1st gear. Two days back I got the radiator changed and also the thermostat valve. No problem when going to Delhi but when coming back the same prob surfaced. Surprisingly the fan is also working. Then I had to make the fan direct so that engine gets cooled continuously and filled the radiator with water. I've fitted my car with cng last year. What should be done?