Ok I have read every thread on the forum on this subject. Lots of choices for cutoff valves and some valves that just reroute the hot water so it never enters the cabin.

I live in Houston Texas so it gets a bit warm here in the summer months and freezing some times in the winter. I had a 1968 BB and I cooked in that thing. I now have a 1970 350 with AC and want it to be cool (or cooler) than my previous experience. There are other things I can do to make this better(Lizard skin, thermal blankets ect) but I want to concentrate this post on just the heater core.

A couple of questions:
1) If you use the 3/4 ball valves will this cause back pressure issues with the water pump that will lead to failure and/ or performance derogation.(Dahl 3/4 crimpex X 3/4 crimpex 063-3750-6 mini ball valve)

2) If you use the bypass valve (AC Delco 15-5533 or Factory Air 74809 vacuum control heater valve)) will it only work when under vacuum and once you turn off the car you loose vacuum and hot water will rush back into the core.

3) Installation: All The valves are 3/4" where your heater hoses are 5/8. Is there a special setup to use these 3/4" valves with the smaller heater hoses? Do you just use a little soap and push like hellllll to make them fit.

I wish the stock setup would correct this but it is just not efficient. I purchased a new stock valve(not installed) but once vacuum diminishes hot water will enter back into the core/ cabin.

I welcome your answers to these 3 questions and any other suggestions that would help me make the right decision. I only want the Heater core to be hot when I want it to be hot. Hopefully some of the senior members can chime in on this.

 

I have used a lever type ball valve for 2 years with no issues. The valve came from Lowes and has 5/8 fittings.

 

Same here except I bought an automotive type valve.


This valve is similar to what I found but it did not have the bracket. I just cut hose and inserted inline where the hoses are anchored to the right inner fender. It looks like the bracket is removable.

 

No.

If you shut the car off, first, why would you care. You can't drive it when it's off.

Second how could water rush back in if it's not circulating?

You can buy 5/8" fitting to screw into the ball valve.

 

I did this and it blew out my orig heater core........had it replaced and was worth it to stop the heat

 

This what I did. 2 1/2 years and no problems. Add this on the heater hose connection coming from the intake manifold. I added mine down low near the frame.

http://www.panteraplace.com/page152.htm

 

If that's all it took to blow out the heater core, the core was junk to begin with.

 

i've had no problem with my shutoff valves but i have never shut them either.i replaced the vacuum shutoff valve and found it will stop the flow when the a/c is in max air position.the rest of the positions coolant will flow and i believe this is a good thing to extend the life of the core.

 

I started out with manual cutoff valves, but decided to move to a more modern vacuum bypass valve. The main reason was that I wanted to be able to circulate coolant thru the heater core every once in a while.

My 72 didn't come with a vacuum cutoff valve from the factory, so at first I got vacuum from a tee in the control, I'd get vacuum to the valve with the AC on. I wasn't completely happy with that, so when I had the dash apart for something else, I mounted a spare vacuum safety valve from the wiper bay on top of the heater core, and had it actuated by the temp control cable. So now, when the temp control is in the full cold position, the bypass gets vacuum, otherwise it's blocked, and the core gets coolant. So now I control whether or not the coolant flows to the heater core by simply adjusting the temp wheel.

If you go with a bypass valve, I'd make sure to get one that's 'normally open', so that without vacuum, the coolant flow straight through.

 

just installed 2- 1/4 turn ball valves on my heater lines and the AC freezes me out now!

Since I'm in Florida, probably wont need to open them up until December.

 

take the supply hose from the heater and connect it to the inlet side of the expansion tank where the hot water returns from the heater core, and your done. I did this on bb 70, add some water wetter and it run 185-200 max temp and my cabin receives no heat form the core. O and it cost me zero, only issue is that the heater supply line is smaller than the inlet side of the expansion tank so you could use a setup fitting or just some lube and force the hose on. One is like 5/8 and the other is 3/4. IF I need heat or to show car I just put hose back to there correct position just clamp the lines or you loose coolant. Zero cost mod and reservable in 5 min.