MG Sports Cars

Here is a good topic for discussion I think. We've come up with various ways to use the original valve and several aftermarket valves, and here lately I've been seeing comments about something called a bypass valve. What is it, and what does it do? What configurations is it available in? Is there a ready source that is good for our applications?

Those are my questions, as for answers I have some speculation and maybe some of you can elaborate on it. I think the idea is to prevent hot water from entering the heater core from either the supply or the return hose. Apparently even with the supply hose turned off a significant amount of heat can get in from the other side. So does a bypass hose turn off both sides at the same time? Does it connect the supply and drain hoses together (why would it?) or something else entirely? I'm ready to hook up my heater and would like to know. A new heater control valve would be good, the right one would be better.

Jim

Here's an electric one

[www.lategreatchevy.com]

Looks interesting but does it allow partial opening to control heat? The description says it uses a "switch" which would seem to indicate on/off operation.

On the plus side, if it *can* control the opening it might not be hard to fit into the stock control position in the dash.

Jim

Since it can be used to replace the stock vacuum unit I would imagine that you could modulate it for heat control. I'd call the vendor ans ask.

The more I think about it, the more I think the original cable control is just fine, at least for now. But the valve only controls one side. Chrysler had a 4 port valve Everco # 74643 but I have no idea how it worked internally. Seems to me you'd want to completely shut off the flow on both sides of the heater core at the same time and at least for the older type coolant systems most of us are using, bypassing the flow would bypass the radiator too so shutting it off completely would seem a better answer as it would not decrease the cooling of the system by bypassing the radiator.

I'll probably re-use my old cable controlled single valve for now, and maybe never change it. But when I do the new dashboard I may want to look at this again.

Jim

Don't know if it helps but I used the original dashboard cable control and an RV8 inline shut off valve and it works a treat. It turns the flow off and on to the heater matrix easily unlike the original MGB valve.
The valve fits in easily in the hose that returns down the side of the inlet manifold to the pump.
Can't see why you would need to shut off both ends to the matrix as once you have stopped the flow thats it. My matrix just goes cold which is what I expected.
However, with louvres in the bonnet when my twin fans come on I get hot air comming through the face vents which will be a useful feature in the winter and will no doubt keep the frost off the screen.

Ian

This is what I have used for the last 7 years:

[www.summitracing.com]

That's the one I'm using.

Using stock 'B' valve with modified bracket on my 3.4L.