93 passat turbodiesel 1.9 litre

i have a 93 passat turbodiesel and i just rebuilt the engine and installed a new cylinder head. when car is idling or driving slow temperature stays steady at around 80c but as you go on the highway the temperature creeps up to around 100c and won;t come down. could it be cause the injection pump is not timed right? please reply.thanks.

Hi.Check your block, coolant drains, pump body for debri first.