Abstract: A heating system is provided, for heating liquid in a truck mounted hot line pavement striping system, including a paint storage tank and spray guns, the heating system including a conduit from the internal combustion engine of the truck leading to a series of smaller conduits passing through the thermal oil bath, as the sole heat source for heating the oil bath, and thereafter being exhausted to the atmosphere, the inner walls of the tubes having sufficient heat exchanging surface, and of sufficient number to conduct sufficient heat from the exhaust gases through the conduit wall to the oil bath to heat the thermal oil, the oil surrounding tubes within the bath, containing the paint to be sprayed "hot" from the paint guns, and a heat by-pass from the engine to by-pass the heat past the heating system.