Took the '76 Shark out for the first time this year, and it was really, really warm in the cabin, even with the tops off and windows down. I drove about 10 miles in 80 degree weather.....

I *think* this is normal....is it?

join the crowd....

Put a shut off valve on both heater hoses. As long as the core has hot water going through it, and it always does, you are going to get a tremendous amount of heat in the cabin. It doesn't matter that the heater is off. The valves are available at NAPA. You need on that is 5/8" OD and one 3/4" OD. It will make a notable difference.
Scott

I have the ones from NAPA, they are nice & compact, makes a big difference. Try it, you'll like it.

anyone have the #'s for those valves?

Mikee, I posted the part numbers for those valves about a month ago, Ill try to find the post.  The parts were on the shelf and the combined price was less than $50.00.  The valves are nice and compact as Scott said and should allow for full flow when open.  I shut both of mine off last week as the temps here were in the 80s.  I'm anxious to see how much difference it makes this summer when its really hot.  I installed mine under the car where the heater hoses make the bend to connect to the heater core.  I initially had them up top where they were easy to get to but didnt like the way they looked, not ugly, but not attractive either.  I now have to duck under the car to turn them off and on but its only twice a year, I can live with that.

I have a Four Seasons number for ya. 5/8" is 84706, 3/4' is 84707. Most auto stres use that brand.Personally I would just put one on the inlet side. I've done that on a lot of cars. If you put it on the hose comming from the block it will keep the water from flowing through the heater. Other than that like Mick says, I put down some foil back insulation under the carpet & in made a world of difference. However, I was replacing the carpet at the time. Terry my7T12007-03-29 05:30:38

I installed mine up top and put new short hoses between the valve and engine so that the new hose see's the pressure. My heater hoses were old and this way I only had to put a short new hose on. I leave the valves shut almost all the time so I'm not worried about the older section of hose. I had one valve on last year and it was down low and the section that was under pressure split open on the way home from Pigeon Forge. That won't happen agaign!