"Joe" wrote: (1994 Ranger 4.0L )
AutoZone computer says 16 Lb. radiator cap is specified
for my car, but Mitchell book says 13 Lb. Which is right?
Will my 16 lb. cap have too much pressure and cause
leaks that might not occur with a 13 lb. system?
I recently changed out the water pump. I used a torque
wrench and tightened the bolts down evenly but I now
see a leak at one of the attachment bolts. Could my
16 Lb. cap be the problem?
The water pump leak problem has nothing to do with the
cap. Assuming that the pump gasket was not damaged
at installation, the leak is probably water working its way
past the bolt threads. Remove the bolt, coat the
threads with sealant and reinstall it.
A pressure radiator cap is used to raise the boiling point
of the engine coolant so that it remains liquid instead of
turning to steam when heated. If the liquid flowing in the
engine block turns to steam, its ability to carry away heat
The coolant's boiling point is raised about 3 degrees per Lb,
so a 13 Lb cap will raise the B.P. of (50/50) coolant from
222 deg F to 261 deg F. A 16 Lb cap would yield 270 deg F.
The 16 Lb cap provides somewhat better protection from hot
spots being developed in the head/block casting. The engine
and the hoses can easily withstand the pressure.
I can't think of any reason to use the 13 Lb cap, but I don't
own any cars with the modern plastic radiators, so I don't
know how fragile they may be.