- Oct 14, 2009
- Potomac, MD
- First Name
- Willys Model
- Willys Year:
The short answer is that the original cooling system was designed for 7lbs. At 15lbs you’ More than doubling the pressure in the system. You can cause gasket leaks, etc. when I switched to my champion radiator, I was using the 15lb cap, and it wasn’t cooling right and was always hissing after a drive. I switched to the 7lb cap and everything was good.
On page 118, paragraph H-4, it says: "Early production vehicles were equipped with 7 lb. pressure caps; later vehicles with 9 lb. [0,63 kg-cm 2] caps. Current production Model L6-226 4WD and 4x4 vehicles are equipped with 13 lb. pressure caps; all others with the 9 lb. caps." That's fine except it doesn't make clear what years or serial numbers are included in the categories of "early production," "later production," and "current production."
Since my wagon is a 1960 I'll assume it's not "current production" and is part of "later production," and should be equipped with a 9 lb. cap.
However, I'm using a 16 lb. cap. When the original radiator and heater cores were re-cored, they were pressure tested to 30 psi so I'm not concerned about them failing, nor am I concerned about coolant system hoses, gaskets, etc. The 7 lb. increase in system pressure, with a 33% ethylene glycol mix, increases the boiling point to about 260°F (about 15 degrees more that at 9 lb.) For me, the biggest benefit of a higher boiling point is the prevention of localize boiling at hot spots around the combustion chambers. The lower anti-freeze concentration (from the usual recommend 50:50) is better heat transfer.
If under max power (not there yet) the coolant was to suddenly boil around the combustion chamber, detonation (and engine death) would be he likely outcome.
It would be interesting to know what made your engine "hiss" with the 15 lb. cap. When you say "wasn't cooling right", do you mean overheating?