Radiator caps

["Alex" <tid.rum@swipnet.se>]

Dear friends,
I have been following the discussions about radiator caps and I want 
to share the following experience from my V-12:
The cap on the overflow tank works as a pressure relief valve. When 
the pressure exceeds the spring force coolant will flow by the valve 
and evacuate through the hose connected to the filler neck on the 
tank. The cap is also sealed to the top of this neck, preventing 
coolant from overflowing out in the engine compartment.
Then check the cap on the filler neck on the engine. BOTH the lower 
pressure valve seal and the upper seal seals off the neck.
It is double sealed!!!
The bleeder hose from the radiator is connected below the cap, and is 
not affected by the same.
So even if this cap is lower rated than the one on the tank, coolant 
cannot escape out in the air through the two seals, unless of course 
the upper seal is broken and the system is pressurized over the 
rating of the cap.
The most important thing must be a correct rated cap on the overflow 
tank.

Alex
'86 XJ-S V-12

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