411 Radiator Caps

[peter dowdle]

Can anybody tell me for sure what radiator caps I should use on my 411.There seems to be varying opinions as to what to use on the radiator and what to use on the catch tank. Some say a blanking cap on the radiator and a pressure cap on the catch tank. Other have the reverse idea. Does anybody know what the factory set up was ?

Regards Peter Dowdle

[Geoff Kingston]

Peter,
Blank cap on the rad pressure cap on the catch tank, that was the set up on my on my 410 and 411 now sold and my two current 603's.
Geoff.

[peter dowdle]

Geoff that is wat I have been using. I dont have any leaks in the system but when the radiator is cold I check thelevel of water and it is always down a bit .I thought the idea was that it should recover water from the catch tank as it cools leaving the radiator full. Any thoughts as to why?
NB I leave the catch tank about half full.

[peter dowdle]

The word is WHAT

[Kevin H]

411 owners manual says 13 psi cap on the expansion tank. It doesn't say what the cap is on the radiator.

[Barrie]

13lb pressure cap on expansion tank and plain cap on radiator.

The plain cap is to refill the radiator only.
The pressure cap is to allow excess pressure in the system to vent.

Expansion of the water from the radiator sends it into the pressure tank and returns when it contracts.
If pressure gets above 13lbs sq inch above bar, first air, then water vent through pressure cap on the expansion tank.
If you put the pressure cap on the radiator then the water in the radiator will only flow to the expansion tank when the pressure is above 13lbs sq inch and, crucially, it cannot return as the pressure cap is a one-way valve and so any water which makes its way to the expansion tank cannot return thus negating its reason for being.

Pressure caps on radiators are only for systems with no expansion tanks.

PS there are at least two different depths of pressure caps. If yours is too shallow it will not allow pressure to build up and so overflow more easily. Identification of the correct one is by observation and feel: when you insert the cap it should protrude above the rim of the aperture and you then press down to compress it and then turn it to close. Also note that the springs in the cap weaken over time so should be replaced regularly.