Radiator cap pressure

[Andrew]

Hello all

I have been running my 1360 Herald with a 13 Lbs radiator cap.  Unfortunately the radiator sprung a leak so bought a new one from a very Reputable supplier.  The new radiator was fitted with a 7 Lbs cap.  Car runs OK but what is the difference between the two regarding running temperature and are both OK.  (The first one to say the difference is 6 pounds wins the bobby prize )

[Clive]

The 7lb cap means the water will boil at approx 110 degrees (less than with the 13lb cap which would be about 120)

Figures above for water, antifreeze mix will increase the figures a bit.

The change of cap will have zero affect unless you get to 110degrees....in which case you will have other things to worry about.

[Pete Lewis]

other things to dream about is the hoses and radiator and heater need to be ok to run at 13lb

7lb  is more normal  for cars like the herald ,  the higher  rated cap may have induced the leak ???

Pete

 

[johny]

yes your car may only run at 90º so the running pressure wont get near 7lb but our systems arent sealed ones as they use an overflow bottle. What this means is that on starting the engine the system (which should have no air in it) warms up and the water expands slightly and must find an escape. It can generate an enormous pressure but in our case only reaches a pressure sufficent to open the radiator cap so that the excess can be dumped to the bottle. Therefore the greater rated cap used the higher the pressure the whole system (radiator, hoses, core plugs, head gasket, water pump seal etc) is subjected to.....