OK
The heater core will only get warm, the engine temp on the temp gage never gets above 1/4 of the way up.

I installed a new radiator last year. Prior to this I never had a problem with the heater. Even in the middle of the summer it never got above 1/4 of the way up the temp gage.

 

Replace your thermostat, it's stuck open.

 

If you van is a generation-2 replace the thermostat with a 195 degree, but don't go lower than 180 degree since the computer will get messed up with the readings and the engine wastes mega amounts of gas.

Also, only use DISTILLED WATER in the cooling system. Tap water will deplete the coolant inhibitors fast and the cooling components with the engine will not have the correct protection against corrosion.

Did you check the mixture ratio too?

 

heater is blow cold air