florencethedog Posted March 5, 2017 Report Share Posted March 5, 2017 (edited) Hi guys, im after the best place to get some replacement header tank rubber caps for our 1.5 bmc and is there anywhere I could get a full set of hoses for the old girl well just for spares. cheers stav Edited March 5, 2017 by florencethedog Link to comment Share on other sites More sharing options...
Tony Brooks Posted March 5, 2017 Report Share Posted March 5, 2017 ASAP Supplies or Calcutt Boats. Someone else will be along to explain which make of cap (Polar or Bowman) tend to fail regularly and how to stretch the other make to do the same job. I would never run a 1.5 with more than a 6psi pressure cap (radiator cap) because of those end caps and would go lower or non-pressurised cooling if it did not spit loads of coolant out. Link to comment Share on other sites More sharing options...
florencethedog Posted March 5, 2017 Author Report Share Posted March 5, 2017 Cheers, We have just put the boat in the water and the cap went after afew miles and compared too the other cap this one looks new. I await an expert to guide me lol Thanks stav Link to comment Share on other sites More sharing options...
Peter Reed Posted March 6, 2017 Report Share Posted March 6, 2017 17 hours ago, florencethedog said: Cheers, We have just put the boat in the water and the cap went after afew miles and compared too the other cap this one looks new. I await an expert to guide me lol Thanks stav Mr Tony Brooks in the post above yours,is an expert. Link to comment Share on other sites More sharing options...
bizzard Posted March 6, 2017 Report Share Posted March 6, 2017 (edited) If very fine chicken wire or similar is molded tightly around the caps and secured with an additional hose clip, it will prevent them expanding too much under pressure. Edited March 6, 2017 by bizzard Link to comment Share on other sites More sharing options...
Tony Brooks Posted March 6, 2017 Report Share Posted March 6, 2017 1 hour ago, Peter Reed said: Mr Tony Brooks in the post above yours,is an expert. Not really - on those rubber caps. We converted all our hire boats to keel cooling, removed the heat exchanger tubes and had the places where those caps fit caped by a welded on aluminium plate. No more split rubber caps. I THINK its the Polar caps that are poor and the Bowman ones are better but a bit harder to fit.Don't quote me on that - confirmation from others please. Link to comment Share on other sites More sharing options...
alan_fincher Posted March 6, 2017 Report Share Posted March 6, 2017 (edited) 52 minutes ago, Tony Brooks said: I THINK its the Polar caps that are poor and the Bowman ones are better but a bit harder to fit.Don't quote me on that - confirmation from others please. Spot on, Tony. The end caps still branded Polar are modern copies, using old Polar moulds, (Polar no longer exist, I think). They are crap, and balloon after a year or two, and split on one of the poorly made seams soon after. It is not always obvious they have split, as it tends to evaporate fast enough that you don't actually see a dribble, (at least at first). The Bowman cap can be persuaded on to a Polar tank, (remarkably easily, actually), is much better made, and far less expensive. We ceased to have problems once we discovered this, but until then were splashing out on a Polar cap every couple of years. IMO it is also best to run with a pressure cap, "radiator cap" of 3 or 4 psi, and absolutely definitely no more than 7 psi. At 4 psi it should never come close to boiling, if thermostat works and skin tank adequate, so why exert a greater force on these caps than you actually need to? Note if swapping pressure caps there are both "long reach" and "short reach" types, and you must get the right type for what you are going to attach it to. EDIT: The cap pictured is the blanking one, with no take off I think. I have never known these to fail. It is the one that has a take off for a pipe that does - almost invariably on the seam joining the outlet to the rest of the cap. This is possibly exacerbated if the weight of the attached hose pulls unevenly at the pint where the two "rubber" parts are seamed together, but I was never able to get longer life from a cap, by "jiggling" how the hose entered it or was supported - the "copy" Polar caps are designed to fail, IMO. Edited March 6, 2017 by alan_fincher Link to comment Share on other sites More sharing options...
Tony Brooks Posted March 6, 2017 Report Share Posted March 6, 2017 Thanks Alan - I thought it was you who has to keep repeating this advice but could not be sure. Link to comment Share on other sites More sharing options...
Ray T Posted March 6, 2017 Report Share Posted March 6, 2017 2 hours ago, alan_fincher said: Spot on, Tony.The end caps still branded Polar are modern copies, using old Polar moulds, (Polar no longer exist, I think). They are crap, and balloon after a year or two, and split on one of the poorly made seams soon after. It is not always obvious they have split, as it tends to evaporate fast enough that you don't actually see a dribble, (at least at first). The cap pictured is the blanking one, with no take off I think. I have never known these to fail. It is the one that has a take off for a pipe that does - almost invariably on the seam joining the outlet to the rest of the cap. This is possibly exacerbated if the weight of the attached hose pulls unevenly at the pint where the two "rubber" parts are seamed together, but I was never able to get longer life from a cap, by "jiggling" how the hose entered it or was supported - the "copy" Polar caps are designed to fail, IMO. I replaced the endcaps on my oil cooler late last year. I was surprised how much the original ones had distorted: Link to comment Share on other sites More sharing options...
bizzard Posted March 6, 2017 Report Share Posted March 6, 2017 Beats me why these hoses and caps are not fabric reinforced like vehicle hoses to stop expansion and deformation when under pressure. Link to comment Share on other sites More sharing options...
Theo Posted March 12, 2017 Report Share Posted March 12, 2017 (edited) I have never had to replace Theodora's Bowman caps in 5,000 hrs of running since we bought her. I don't know how old they are. Soon after we bought her I modified the cooling system and as a consequence of the mod the excess pressure in the whole system is governed by the height of the system expansion tank, about 5 feet above the rectangular header on the engine. So, yes, use low pressure and Bowman's. Nick Edited March 12, 2017 by Theo Link to comment Share on other sites More sharing options...
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