Van was running great. Running down interstate at about 68 mph and it started running a little warm. Eventually ran hot. Let it cool, changed thermostat, checked water pump, it was fine. Now it is running ok, but very little heat inside van with engine temp at normal range. Wondering where else to search for problem? Thanks

 

Was the coolant rusty? It sounds like some deposits in the cooling system got dislodged and the heater core is partially restricted. You can flush it with a garden hose and a nozzle with a small tip,cone shaped. Clamp off the two heater hoses going into the firewall and remove the hoses from the heater core. Flush it in both directions. There are other possibilities but that fits with the episode.

 

I'm not sure if the coolant was rusty or not it was in the middle of the night at a rest area. I will try the flush-out tomorrow. thanks so much for the advise!