caltex coolant is good choice for cuore. it is good quality long life coolant. before changing coolant, flush system with clean water 2-4 times till clean water comes. check that hoses r in good condition. change weak ones. drain, fill water, start engine for 2-3 minutes and drain again. then refill with coolant. take car to place where front is high and idle for some time so that air escapes.
on petrol only car runs very smooth, even if there is no performance gain. but CNG is for economy. i only use it for long routes.