overflow bottle or wiper wash reserve?

[types26/36]

[quote="rgh0"]Brian
To pull fluid back into the radiator reliably requires a "recovery" cap with a second rubber seal around the neck of the radiator filler so it sucks the fluid back in from the reservoir and not air from around the cap. [/quote


Tried that with a cap that had the rubber seal in the top of the cap, still wasn't happy with the results (probably crush height wasn't right) but with the pressurized expansion tank it works fine, used the expansion tanks from the Austin/Morris 1100/1300 range of cars of the 60's. Nice little brass (painted black) tank.
Brian

[hatman]

Eureka! Thanks to John and Brian's patience, persistence and ability to communicate in the words of one syllable with which I am reasonably comfortable I now understand.

I've had a butchers at my filler cap and - whaddya know! - you're right, there is provision for pressure equalisation via a return valve. I am truly grateful to the pair of you - respect is doo!

[marcfuller]

Jeff, Regarding what was original, below is a pic from my S3 originally sold in Kentucky. The car is very original (except for the conversion to DHC). I think that this is how it was prepared by the distrubutor/dealer. It has two of these Tudor bottles one for the windscreen washer on the left inner fender, and one (pictured) for coolant overflow in front of the radiator. I think Doug's installation of the aluminum bottle looks a lot better.

[hatman]

Having, at last, seen the light with regard to the get-backability of the overheated coolant expelled by the system I now think I know why the non-pressurised overflow bottle system that Lotus used aint very good.

When, owing to reduced temperature (and thereby pressure) in the cooling system the spring-loaded pressure valve clangs shut, the space between the radiator seal and the radiator cap 'lid' thereby created will, initially, create a vacuum which the expelled coolant in the pipe will fill and find its way back intio the system via the pressure-release gubbins.

However, the overflow system (pipe, bottle) not being sealed will instantly admit air, which will quickly make its way back up the overflow pipe and from there into the cooling system to equalise the pressure therein. Ergo, it's a 'last out, first in' return system that has a pretty short duration as far as returning the wet stuff is concerned. Am I right?

[types26/36]

However, the overflow system (pipe, bottle) not being sealed will instantly admit air, which will quickly make its way back up the overflow pipe and from there into the cooling system to equalise the pressure therein. Ergo, it's a 'last out, first in' return system that has a pretty short duration as far as returning the wet stuff is concerned. Am I right?

Ermm! no I dont think that is the answer, if the end of the pipe leading from the radiator overflow pipe into the bottle is submerged in water (that has been expelled from the radiator) then it should not be able to draw air back, the vacuum created should in theory draw water back in to the radiator.
(Sorry if I am not understanding your post )
Brian

[hatman]

Your understanding is spot on Brian and I can see that you are right about the impossibility of air getting into the pipe when the end is submerged. If, however, I'd marshalled my thoughts a little more before leaping for the keyboard I'd have suggested that as soon as the seal whaps back into place air can then leak under the 'lid' of the filler cap which, although it sits on the top of the radiator filler neck, does not actually form an airtight seal. This ingress of air will then destroy the vacuum effect that previously existed between the radiator and the overflow bottle, thereby terminating the returning flow of coolant. How's that?

[john.p.clegg]

That is why I've a thin rubber washer in the lip of the rad cap
John

[types26/36]

air can then leak under the 'lid' of the filler cap which, although it sits on the top of the radiator filler neck, does not actually form an airtight seal. This ingress of air will then destroy the vacuum ?

Yes,this was is what Rohan was refering to in a prevous post and what John has done to cure by adding a seal (and I tried) but it didn't work for me, I accept it should work but the pressurized tank is my solution
Brian

[type36lotus]

I simply bought an off the shelf radiator cap of the chosen pressure. It came with the rubber gasket and works quite well. I believe it may have stated "for recovery systems" or the like.