Club 80-90 Forums

Hi, wonder if anybody can help me please?

I believe that the coolant header tank with the Dalek cap is pressurised, but the top up tank behind the cat flap is not.

Looking at my Dalek cap, there does not seem to be any sort of valve to the outlet pipe. Is there something missing? Or should there be some sort of valve in the pipe which runs between the two tanks? With the parts I have, I don't understand how the header tank is pressurised.

Thanks in advance for any advice you can give me.

Alex

The valve is part of the cap.

Thanks Rob,

Looking at the underside of the cap, there is a valve and there is also a hole. The hole connects to the outlet spigot but there is nothing in between. I can blow air through with no obstruction. This is what puzzled me, I wondered if there should be two little valves, what I have is one valve and one hole... Does this seem right? I guess what I'm not understanding is that if this is correct, how does the expansion tank get pressurised and the top up tank doesn't?

Alex

So, searched the forum and read how blowing into the cap should make a noise like an elephant... It doesn't!

Shaking the cap I can hear something loose inside, and looking through the little hole I can see a loose spring...

So I reckon this one is knackered.

Can they be taken apart? It's not obvious how...

Alex

They are not that expensive but DO NOT GET ONE FROM GSF they don't work.

Ok, thank you Kit

Get one from brickwerks.They work

As said..if in doubt replace it..as for your cooling system, it should become pressurized when hot and the engine is running, that includes the main tank but not the topup tank behind the number plate.
When the cooling system reaches around 1 bar (over normal) the valve in the Darlek cap opens, allowing excess coolant (coolant expands as it is heated creating pressure in a sealed system) to flow into the top up tank.
As the engine cools the coolant contracts (becomes smaller) drawing the 'overflowed' liquid back into the main system.

Without pressurisation your coolant boils around 100 degrees C. With around 1 bar pressure (over atmospheric) boiling point rises to around 120C which means the same capacity of coolant can absorb more heat energy allowing cooling system design to become smaller and more compact.

As the normal running temperature of an engine is typically around 85 - 95 C, the coolant would be dangerously close to boiling and as gas bubbles in the boiling coolant are NOT a good conductor of heat, this would be lead to localized hot spots and massively high temperatures of components, literally melting metal surfaces and seizing components together.
Increasing the coolants 'boiling point' reduces the likelyhood of it boiling...engines NEED to pressurise if the coolant is to stay a liquid and cool the engine effectively.

Martin