Actually, the spec is14psi on the 60, but I often put a lower
pressure cap on an older car to protect the rad. If the rad is solid,
and the heater core is solid, and the hoses are good, you should be ok
with the 14 lb cap. But that's a big if.
If the temperature is well under 210F with the air on, you don't need
the heavy cap - and that's not nearly as big an if, generally
The only way to increase the system pressure would be to change the
thermostat to a higher temperature one so increasing temperature as
well as pressure.
You would then have to change the radiator cap too. But changing the
radiator cap alone wouldn't change the pressure but in the event of
engine overheat/pressure would negate the protection it gives.
Very unwise, you may get hoses bursting and engine overheating .
If your engine is overheating there is a problem with the radiator
(blocked) or the thermostat not fully opening.
Possibly slack belt (drives the water pump).
Electric fan (or it's thermostat) if it has one faulty.
Waterways in cylinder block/head blocked/corroded.
Dumb as ever. The current cap releases pressure at 7 PSI when
the car overheats. He's proposing changing it to 13 PSI so that
when it is overheating, it will not release until that higher pressure
is reached. That results in a higher pressure when overheating
exactly as he claimed and doesn't require changing the thermostat.
Dumb as ever. When the engine overheats, which is what he's
specifically concerned about, having that higher pressure cap will
result in higher pressure.
That part is correct. Even a stopped clock is occasionally correct.
Harry, you are incorrect on this. The cap alone WILL cause most
suystems to run at a higher pressure as long as the vehicle runs at a
minimum of 160F. The thermostat only controls the MINIMUM operating
temperature of an engine, so even an engine with a 160 thermostat can
run at 195F, or higher. The cap allows the pressure to build to a
MAXIMUM of the rated pressure - at which point it releases into the
overflow to regulate the pressure.
Or bad timing, or bad mixture, or simply overloading the engine. But
yes, you got ONE thing right - installing a cap with a pressure higher
than the system is designed for CAN cause problems with hoses,
radiators, heater cores, etc..
Lots of comments--my two cents: First of all, the water pump is a
centrifugal pump and as such the pressure rise across the pump is a function
of it's speed. The flow output of the pump is a function of the system
characteristics-- Pressure drop vs Flow So changing pressure caps and
thermostats will not change the operating behavior of the pump. The purpose
of the pressure cap is to raise the boiling point of the fluid. This allows
you to run the coolant at higher temperatures (greater than 212F) without
causing it to boil. Just because you have a 180 deg thermostat doesn't mean
that the coolant at running at 180 deg-----because of the cap, typically,
the coolant boiling point is closer to 234 deg F (or higher). That's why
they say never to remove the cap until the coolant cools down--if you remove
the cap too soon, the system pressure becomes 15 psia (atmospheric). the
boiling point becomes 212F and you get a great big flash of steam as the
coolant immediately changes from a liquid to a vapor. As the coolant
temperature increases, it's density (Specific Gravity) decreases and because
it's weight remains constant, the only other variable is it's volume which
increases. Because the cooling system volume is fixed the coolant pressure
will increase (no room to expand) from atmospheric to whatever the cap is
set for and then it is vented to the over-flow bottle.
The downside of increasing the pressure cap setting over what's specified is
two fold---At the higher cap setting, all the system components will be
subjected to pressures beyond design intent--not a good idea. The same
applies to the operating temperature. In summer like days the coolant
temperature will go beyond normal design intent. In both cases, you're
moving in a direction to accelerate component failures.
I didn't want to make the original post into a novel but it appears a
lot is being read into what wasn't included. That car is not having
any problems at all right now. I'm just looking at increasing the
factor of safety against overheating because I just added AC to it.
Non-ac cars use a 7 pound cap and AC uses 13. But it's a 52 year old
car (well maintained) and the downside would be if adding 6 pounds
more pressure is likely to create any leaks, like in the 52 year old
heater core. Nothing leaks now. I'm just torn between being
proactive and getting a higher pressure cap "just in case", or just
sitting tight and seeing how the temperatures run as the weather heats
Like I said in a previous post, a coolant recovery bottle would be my
first step... I never did like seeing that air gap at the top of the
radiator, and it's not good for anything to have it there.
replace "roosters" with "cox" to reply.
On Sunday, April 21, 2013 3:21:32 PM UTC-7, Ashton Crusher wrote:
I live in Arizona, and nobody in my family here has ever
had an overheating problem that wasn't caused by a burst
hose or bad radiator cap, and I know the latter happened
in fall or winter. The hose that broke was a flex hose --
never use those if you don't have to. The bad radiator
caps were brand new replacements -- 2 in a row gushed
out coolant on day one, while the ~5-year-old factory
original cap and a replacement from a car dealer
worked fine. Also I once bought 3 bad thermostats in a
row -- when I tested them in a pot of hot water with a
thermostat, one wouldn't open more than 1/4", the other
two opened wide at about 150F (rated 195F). So for
radiator caps and thermostats, I use only OEM.
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