The car runs fine until traffic or sitting idle for over 10-15 mins. but once i turn the heater on high the problem goes away. then i checked the radiator and there is an oily substance in there. Do i need a new radiator? Thanks
you need to visit a qualified mechanic I think, a new radiator sounds like the least of your concerns.
Oily residue sounds like lower intake manifold gasket, the overheating could be lack of coolant or water due to a leak, more likely the leak at the inlet manifold
