Radiator Cap pressure rating

[RDKeysor]

My recently acquired '60 BN7 was running rather warm, and when I did the inevitable thermostat check, I found the car didn't have one. I already have a six-blade fan, so I opted to remove the radiator and had a shop install a larger core. As seems to be the practice here in Florida, I reassembled everything and did not install a thermostat. On a recent drive, temperature about 75 degrees, the temp gauge went to just past 190 degrees while running continuously about 55 mph. That is a good running temperature, but I am concerned about running it when the ambient is higher. I have Norman Nock's Austin-Healey Tech Talk book, and I find that he favors running a high pressure radiator cap. The one I'm using is marked 7 lbs. Along with considering going to a 12-lb. cap, I'm also considering installing an overflow canister behind radiator. Any observations from those more experienced with this situation.

 

[TimK]

Use of a thermostat or not has been the subject of earlier threads. Thermostats provide the necessary restriction to allow the coolant to circulate at the proper speed to allow the radiator to do its heat exchange work. I use a sleeved (original style) thermostat available from British Car Specialists and others. The sleeve is necessary to close off the recirculation port that bypasses the radiator. Operating without a sleeved thermostat does not fully utilize the radiator. A 7 lb. cap works fine and would only come into play if the temp exceeds 212 deg. A higher rated cap would not cool anything, it would just raise the boiling point of the coolant and allow your oil to heat up to a potentially harmful level. My system (re-cored 14 fins/inch radiator, 6 bladed fan with shroud, and sleeved thermostat with 7lb LONG NECK cap keeps my system below 200 deg. in the warmest temperature in Dream Cruise (August crawl) conditions. If you don't have a long-neck cap (used on some trucks) you won't have any pressure at all.