So the heater in my 68 doesn't seem to get very hot. Is this normal for these cars? I've replaced the heater control valve and it is clear there is hot coolant running through it and to the heater core. My blower motor runs well and puts out a lot of air but it is always lukewarm at best. Short of tearing apart the heater box and taking out the core, are there any other typical things to check before I embark on that endeavor?