Thread: Radiator overflow bottle on Series III

Originally Posted by pfillery

....................... I guess I need to find where the water is leaking - I think it is around the top hose where the pitot tube for the thermal fan is fitted in past the hose (little bits of crusty white discharge on the hose).

Any tips for setting up the overflow properly?

Your problem is probably caused by an air leak not so much a water leak. Youre right on the money with your crusty stuff on the 'pitot' tube. A good way to seal this is to use butyl rubber, you don't need much, to go round the 'pitot' tube inside the hose. If you haven't got any stop and have a chat with the next Telstra linesman you come across, they use it for sealing cable joints. Next make sure you have a recovery system radiator cap, should have rubber seals top and bottom and a valve at the bottom. If the top rubber is crook the coolant won't suck back. Check the overflow hose and its connections, a tiny hole mightn't leak water but may allow air to suck in as engine cools. Hope this helps.

Deano

pfillery

You need to check a couple of things about your system.

• firstly make sure that you have the correct cap with a good seal on the top and in the bottom so there are no air leaks.
• Then check that the hose to the bottle and the bottle itself do not have any cracks or air leaks.
• Lastly make sure the hoses between the radiator and bottle and also the bottle overflow are not blocked.

If any of these things are not correct the radiator will not be able to exchange coolant with the bottle and the system will merely suck air and spill coolant outside the system.

I actually have the same issue with my 101 system. The overflow bottle is low down on the chassis about 2' lower than the radiator cap and is not part of the pressurised system. The radiator uses a standard radiator cap and as such, if the coolant gets hot I can see how the pressure can lift the seal in the radiator cap and allow excess fluid to flow into the overflow bottle - however when the coolant cools and I cannot see how the radiator is able suck the coolant back in as the radiator cap remains shut under negative pressure in the radiator.

The system is different to say a V8 Disco one or my Freelander where the overflow bottle has a pressure cap, is part of the pressure system and there is no real radiator cap in the radiator.

Garry

Garry

Don't underestimate the effectiveness of negative pressure. We have all seen the science demonstration where the instructor boils water in a can until there is steam coming out of the can. Then they remove the heat source and screw the lid on. In a very short time the can crushes by the atmospheric pressure pushing in on the can. 14PSI can support a sealed column of water to 32 feet from memory.

I used to think that all pressure caps were the same though the pressure setting was different.

When I had my SIIB radiator re-cored at J.J. Smith radiators in Sydenham (had been there for scores of years) I asked for a new cap and he asked it had a reservior bottle and got a different cap to the one for the pressure reservior type. So there must be some difference, and I believe it is in the double seal.

Perhaps you should check with a radiator service.

Diana

No matter where your overflow tank is you should have a recovery type cap on your radiator. The perimeter seal allows vacuum to suck fluid back from the reservoir providing the hose to it is leak free as mentioned. The rad cap should have a smaller button in the centre which lifts easily under slight vacuum in the rad. It should be lifted and cleaned with a rag every time you do a service.

Pic of a recovery cap with a scrap of paper under the centre button.

Thanks for the information - in light of that I went and checked the cap on my spare new radiator and while different to the one in the pic it does have a small central button in the pressure cap that allows fluid to be sucked back into the radiator when it cools.

The cap on my actual radiator is different and does not have the central button so somewhere along the line it has been changed. When I get motivated and put my water pump back in an put all the rest of the gear back in I will replace the cap with a correct one.

Thanks for the help - has solved my issue.

Garry

Originally Posted by garrycol

...............................- however when the coolant cools and I cannot see how the radiator is able suck the coolant back in as the radiator cap remains shut under negative pressure in the radiator.

Garry

Gary, my Jeep has the same system. The trick is in the radiator cap.



At the bottom of the cap is a little valve (shown held open with little screwdriver) that gets sucked open when the radiator coolant cools and contracts. This allows suction back down the hose to the overflow bottle to suck the fluid back into the radiator.
Don't know what you mean by a 'standard' radiator cap, if you don't have a 'recovery system' cap (like in photo) recovery won't work.

Deano

Story of my life, too slow. What bee utey says.

Deano