Heater bypass valve, what is their intended function?

[Stridey]

In my attempts to cool the cockpit in my 7 I learned that more modern 7s have a by pass valve and a cable control to the cabin. I'm not sure whether this is only on newer heater versions, ones with the centre louvres on the bonnet.

After experimenting with blanking plates (sheets of cardboard) and perceiving a drop in cabin heat I decided to take the plunge and fit a bypass valve from a TX2 taxi in myself. I used a short cable from an old school mini to put the pull knob just by the steering column.

i perceive a drop in running temp now it's fitted and been for a drive, I'm wondering why this might be, maybe it's just because it's cooler anyway today? Any way the temp guage is  a few degrees lower.

im wondering what the intended advantages of the by pass are, why did Caterham feel the need to add one? Bit dumb I know, as I've now got one anyway....! 

After:

[DJ.]

The idea behind the valve is that the heater matrix is isolated from the hot water, so air passing into the cockpit isn't heated. With an external air intake through the bonnet, the heater fan can draw cooler air in if the heater is off. The reason it diverts the flow is to keep the water circulating correctly, a valve that just blocked the flow wouldn't be a good idea.

 

[Drumster]

My '93 x/flow with the flat-top circulating air heater had a heater valve and as far as I'm aware it basically acted as a switch to turn the heater on or off by diverting the coolant in the system through the heater matrix and the fan switch then simply blew the resultant hot air into the footwells. Opening the valve was always a good way of cooling the engine when it got hot by diverting heat away from it via the heater into the footwells.

Having said that I removed mine in 2007 as previously mentioned.

[Stridey]

Interesting... Wondering why my 96 didn't have one. It was bought as a kit, but assembled at a dealer.

DJ, sort of what I was thinking, simple plumbing. The fan on my old style heater seems to have to power of a gnat coughing though... Should I be feeling a breeze down there, or more of a 'waft'?

Aeroscreens, as I use it I. Town and also on the traffic jam that is the M25 the heater may give me an extra margin for cooling a V hot engine. But pleased to report yesterday it was running around 80, up to 90 in slow moving traffic, then just under 100 when it was really hot in the afternoon and in standing traffic.

As, in my dreams, I see myself in the French Riviera on a blistering hot day I think I'm making progress.

 

[DJ.]

The new style heater and fan is very effective, but only up to about 50mph, after that cockpit drafts suck all the heat out