Mk1 stag - chassis LD242 - early Mk1 cooling system. On the road after long, long restoration, gradually summoning up the courage to go further and further from home 
The only way I can think of filling the system completely, after filling the radiator and putting the cap on, is to syringe water through the air bleed valve into the top hose.
If I do this and then go for a drive, I get about about a pint (maybe a bit less) of water expelled into the overflow bottle (remember, unpressurised in the Mk1), an empty top hose and room in the top of the rad for more water.
The expelled water can then be put back into the rad and syringed into the top hose, and the system is now full again. There seems to be no net water loss.
I suspect on the next drive the same thing will happen.
I have a 13psi rad cap fitted...
...I note that LDpart's description of their Mk1 rad cap says "In the Mark 1 configuration this cap will open when the car is used to allow coolant to expand into the reservoir. It then opens in the other direction to allow coolant to be drawn back into the radiator."
There's no way my rad cap will do that - it's the conventional rubber faced disc on a spring. It will open (upwards) with increasing pressure to send water into the overflow bottle but I can't see at all how it would allow water to be drawn back as the engine cools and the water pressure goes down?
Maybe I just bought a standard 13psi cap (can't remember where I got it - was so long ago!)? Unfortunately the LDpart picture doesn't show the underside of their cap to compare with mine - but the tops look the same...
Thoughts?
TIA, Martin
The only way I can think of filling the system completely, after filling the radiator and putting the cap on, is to syringe water through the air bleed valve into the top hose.
If I do this and then go for a drive, I get about about a pint (maybe a bit less) of water expelled into the overflow bottle (remember, unpressurised in the Mk1), an empty top hose and room in the top of the rad for more water.
The expelled water can then be put back into the rad and syringed into the top hose, and the system is now full again. There seems to be no net water loss.
I suspect on the next drive the same thing will happen.
I have a 13psi rad cap fitted...
...I note that LDpart's description of their Mk1 rad cap says "In the Mark 1 configuration this cap will open when the car is used to allow coolant to expand into the reservoir. It then opens in the other direction to allow coolant to be drawn back into the radiator."
There's no way my rad cap will do that - it's the conventional rubber faced disc on a spring. It will open (upwards) with increasing pressure to send water into the overflow bottle but I can't see at all how it would allow water to be drawn back as the engine cools and the water pressure goes down?
Maybe I just bought a standard 13psi cap (can't remember where I got it - was so long ago!)? Unfortunately the LDpart picture doesn't show the underside of their cap to compare with mine - but the tops look the same...
Thoughts?
TIA, Martin
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