Does anybody else keep losing Polar end caps? Does anybody have a solution?

[alan_fincher]

If reducing the pressure in your cooling system is part of resolving the "polar" cap issue - i.e. to reduce the pressure on the polar cap; does changing to a Bowman obviate the need to reduce the pressure?

 

Yes, it may not be necessary, and I'm also aware that if you change multiple things at the same time, you never actually know for certain which change(s) produced a solution.

 

However as Calcutt tell me they now fit a 4 psi cap as "standard", presumably they have come to the conclusion that operating at a lower pressure is no bad thing.

[Barry]

 

Yes, it may not be necessary, and I'm also aware that if you change multiple things at the same time, you never actually know for certain which change(s) produced a solution.

 

However as Calcutt tell me they now fit a 4 psi cap as "standard", presumably they have come to the conclusion that operating at a lower pressure is no bad thing.

 

Fair enough

[BEngo]

Remember that the purpose of the pressure cap is to raise the boiling temperature of the coolant above 100 C . The BMC is prone to boiling in localised areas of the head (IIRC near the valves and injector pocket) even though there are no external signs, so has to have a pressure cap to stop this.

 

Evidently, if the engine is not working hard localised boiling will not be a problem, even with a reduced -pressure cap but out on a river, or, for Alan, in the depths of Blisworth and Braunston tunnels, when working harder the engine may well be at best on the verge of localised boiling. Ethylene glycol is a better coolant than ordinary water ( that's why it's in water cooled aircraft piston engines) as well as being an anti-freeze and can also help prevent localised boiling. It would therefore be a good idea to keep a maximum strength of anti-freeze mixture ( or use summer coolant) in the tank if reducing the running pressure in the cooling system.

 

N

[alan_fincher]

Remember that the purpose of the pressure cap is to raise the boiling temperature of the coolant above 100 C . The BMC is prone to boiling in localised areas of the head (IIRC near the valves and injector pocket) even though there are no external signs, so has to have a pressure cap to stop this.

 

Evidently, if the engine is not working hard localised boiling will not be a problem, even with a reduced -pressure cap but out on a river, or, for Alan, in the depths of Blisworth and Braunston tunnels, when working harder the engine may well be at best on the verge of localised boiling. Ethylene glycol is a better coolant than ordinary water ( that's why it's in water cooled aircraft piston engines) as well as being an anti-freeze and can also help prevent localised boiling. It would therefore be a good idea to keep a maximum strength of anti-freeze mixture ( or use summer coolant) in the tank if reducing the running pressure in the cooling system.

 

N

 

It looks to me from information I have Googled that going from a 7psi cap to a 4 psi one will probably reduce the point at which the Ethylene Glycol based coolant will boil from about 118 Celsius to 113 Celsius, assuming a typical concentration. I'm wondering if that 5 degree reduction is really that big a difference in practical terms in canal boat use?

 

All I can repeat is that Calcutt say their standard fit is now the 4 psi cap, and I know some people run these unpressurised.

 

Anyway, for the purposes of getting going again, I have changed the end cap to a Bowman one, as they suggest. I was able to source that locally, and it can be prised on.

 

I'll have to order in a lower pressure "radiator" tank cap, if I decide to do that, but for now will see how we fare at 7psi but with the Bowman end cap.