I have a 2002 Grand Vitara with 70K. The heat worked fine until this winter. Now the heat seems to work fairly well while driving but promptly after stopping the heat is almost undetectable.

The coolant is full and clean, and the belts are tight.

Any thoughts?

Dan

First cheap-to-fix guess, assuming it really is full of coolant, is thermostat stuck mostly closed.

check that your heater blower motor is working, there should be a fuse for it in the dash, if the thermo was stuck mostly closed the engine would overheat or run hotter than normal at least and the thermostat doesn't stop coolant flow through the heater core, coolant is always circulating through the heater core unless you shut off the valve in the heater line.

it sounds like when my blower motor quit, if I was up driving 40-50mph it got nice and warm in the truck because there was enough air flow at the front of the truck to force through the heater, when you stop the air flow stops and no more forcing through the heater.

Hope it helps, good luck.