Emergency shutoff for heater?

[KevAndAndi]

I'm wondering if it might be a good idea to put a shutoff valve on the engine bay side of the firewall, on the heater core intake hose. As I understand it, the heater valve is on the return side, and hot coolant can work its way into the heater core even when the heater valve is closed (or malfunctioning, of course). Furthermore, as I have read about catastrophic coolant flow incidents into the interiors of Spiders, it seems that a shutoff valve would be prudent.

Thoughts? Does such an item exist? Would it be OK to run with such a valve closed? (I assume so, because that is effectively the same as shutting the stock heater valve, with the difference being an upstream shutoff rather than a downstream.)

I don't really want to take the step some folks do, of bypassing the heater core entirely.

[70spider]

I think that may be a good idea. In the summer it gets fairly hot here, 95-100 w/ 30-40% humidity, and being able to reduce the cabin heat would be a good idea. I have thought about by-passing the heater core intirely but didn't due to the fact we get cold winters (< 40 *F) and plus I like the idea of having a defrost option.

[azruss]

If your heater core, valve and hoses are in good shape, i don't see the point in adding another valve. The heater valve shuts off the water flow, so no hot water is circulating into the heater. You will pick up some residual heat from the under the dash, but air passing though the vent negates most of that.

[KevAndAndi]

If your heater core, valve and hoses are in good shape, i don't see the point in adding another valve. The heater valve shuts off the water flow, so no hot water is circulating into the heater. You will pick up some residual heat from the under the dash, but air passing though the vent negates most of that.

But couldn't you say the same thing about bypassing the heater core? Many people do that. Seems to me a shutoff valve does the same thing and is less drastic.

[KevAndAndi]

http://shop.advanceautoparts.com/p/carq ... fragment-2

I subsequently found this, which is the type of shutoff I was envisioning. I also see via the Google machine that a lot of folks put something like this in their classic cars for comfort and/or emergency purposes.

A drawback is the stagnation of coolant in the heater core. This could be mitigated by occasional opening of the shutoff valve in the summer, and of course keeping the shut-off valve open during the cooler months.

If one were going to do this, it might make more sense to install two valves, one on the heater core intake side and one on the return side. That would truly be equivalent to the bypass. Without the emergency valve on the return side, one couldn't completely isolate the interior from coolant from the engine. Of course, the coolant already on the heater core side of the shutoff valves could still find its way into the interior if there were a leak. But at least one would be able to drive the car.