I have been noticing lately(colder weather) that my 67 with new Vintage air is blowing luke warm air after cruising down the road. The car is running fine with the temp staying in the 190 mark without fluctuation. The heater blows hot for a while after the engine has warmed up. When I drive down the road, it looses it's heat and blows luke warm at best. I noticed that after I got home and let the car idle, the air warmed some but not all the way back. Coolant level is good. I don't adjust anything prior to loosing heat. Any ideas? It's about 35 degrees here. The radiator is 4 core--it wouldn't be cooling too much causing the thermostat to close to retain proper heat would it?