Valve on cooling system vent - why?

[Mole]

When fitted with the standard induction system, my 1.8 k series had a small pipe running from the cooling system "header" tank to the cylinder head via a small valve in the flange of the plenum. Having now upgraded to throttle bodies, there is now no valve, it having been replaced with a plain spigot tapped into the flange of the forward throttle body in the appropriate place.

 

What is the purpose of the valve in the standard set-up and what is the effect of removing it as I have done in fitting the TBs?

 

SV 52 CAT - the mole is awake

[V7 SLR]

In the SLR the spigot contains a little ball valve which is known to fail on occasions (sticking shut I believe). The common approach is to drill out the little ball (which I did) turning it effectively into the same valve-less spigot you now have. Since drilling out mine V7 appears not to have suffered any detrimental effects. I now have direct to head TB's with (I guess) the same spigot as you. Wouldn't worry about it.

 

Worcs L7 club joint AO.//Membership No. 4379//Azure Blue SLR No. 0077//Se7ens List Tours

 

[Mole]

Thanks V7 - I'm not all that worried - just wondered why there was a valve there in the first place

 

SV 52 CAT - the mole is awake

[Bob Corb]

It should allow air to vent out of the cylinder head during filling but during operation any water trying to push past will lift the ball into the valve closing it off, this prevents coolant short circuiting the radiator. In the 7 the cooling is quite good (well mine is) due to the large open grille so its less critical, in an MGF you need everything you can get...and then some.

 

BC