I was thinking of putting a higher pressure cap on one of my cars to
increase the factor of safety against boiling. Looking thru the web
for info on the likelihood of changing from 7 psi to 13 psi causing
leaks I found little on that issue but did find a couple references to
the pressures created by the water pump. One site boasts of a 19 PSI,
$25 cap to get you thru your "hard driving".
Thought I'd see if anyone else has heard of this. The claim was that
the water pump could create over 30 PSI of pressure. Since that is
double the normal operating pressure of most modern cars I find it
hard to believe. If the system was at full 15 psi of pressure while
the car is idling and then your floored it and ran it up to near
redline and created another 30psi of additional pump pressure, or
even 10 psi of additional pressure downstream at the radiator cap, you
would immediately cause the system to have to vent to the overflow to
relieve this higher pressure. I've never seen a car vent due to me
revving the engine up while I'm working on it. Thoughts?????
There is a over flow bottle for coolant/anti-freeze. Ever
cleaned/flushed your rad. and maintain proper level of
coolant/anti-freeze in your rad.? If the car is old, messing with cap
On Apr 21, 11:15 pm, firstname.lastname@example.org wrote:
You might want to rethink that one. Water isn't going to
move through a system without pressure to push it. I wouldn't
expect the pressure to be very high, but there has to be pressure
due to the pump.
As for the question at hand, what is unstated is if there is
actually a problem, ie is the car overheating? If it is, then
finding out the cause of that instead of trying to raise the
boiling point of the coolant via pressure would seem to be
the better approach. For example, if he has a bad thermostat
or collapsing hose, he'd be just covering up the real problem.
On Mon, 22 Apr 2013 05:29:32 -0700 (PDT), " email@example.com"
No, the car is not overheating. It's never overheated. What happened
is that I installed an AC unit in this 60 Dodge. That has made it run
about 10 degrees hotter then it used to, mainly from just having the
condenser there in front of the radiator. So I was thinking about
whether it would be a good idea to go to a 13 pound cap instead of the
7 pound one on it. Just to give a bigger margin of safety when the
temps here get up to 110. The manual for the car lists the 7 pound
cap for non-ac cars and the 13 pound cap for AC cars. Just curious if
anyone has ever seen this increase in pressure cause an immediate leak
to happen. The Radiator was rebuilt 10 years/10,000 miles ago. The
heater core is factory original. Now, on a 95 degree day it's running
up to 205 on the freeway and 195 around town. Thermostat is 180.
I don't follow this. Your radiator is running about 10 deg. F (?) hotter
with the AC, so what? Why is that a problem? You aren't anywhere near the
boiling point of your coolant, are you? Assuming you have a 50:50 mixture
and 7 psi your boiling point is about 255 deg. Changing to a 13 psi cap
would improve things by raising the boiling point to about 270 deg.
Unless you are getting close to 250 I don't understand why you want to do
this. Be sure to check my math. These figures are quick guesstimates.
Sorry, sounds like a waste of money. Keep an eye on the temp gauge this
Summer though till you're sure.
On Mon, 22 Apr 2013 19:40:05 -0400, "David L. Martel"
So far it's not a problem. I've just never run anything with such a
low pressure cap before. Some of my newer cars will run upwards of
235 on really hot days so I'm wondering if this one does will the 250
be enough of a cushion.
into the overflow tank with the OEM pressure cap. Putting in a cap that
cracks at a higher pressure probably won't even change anything with respect
to when the coolant starts to go into the overflow tank. In a closed system
(completely full and cap shut) the coolant pressure increases rapidly as the
fluid starts expanding (without the cap opening the pressure could easily
get up to a 1000 psi). Going from 7 to 15 psi would have a relatively
insignificant change in the way things work. It doesn't change the
operating temperature, just raises the boiling point of the coolant. And
operating at a higher pressure than OEM is moving in a trouble direction.
BTW, one can calculate pressure vs temperature in a closed system--just look
up "Bulk Modulus" and fluid compressibility.
Do the A/C cars come with a different radiator than non-A/C cars?
given the info you give I would think that this should be OK assuming
everything is in tip-top shape. However you may end up replacing the
heater core if there's a weak spot in it, likewise with any old hoses.
You may also want to consider retrofitting a coolant recovery bottle
like modern cars, that way you won't have to constantly keep an eye on
the radiator's water level, and due to not having any air in the system,
should theoretically make it slightly more resistant to corrosion
(although I'd still change the coolant every two years anyway just for
insurance.) You'd need the proper radiator cap for that, so the
radiator can suck coolant back in through the overflow tube when it
replace "roosters" with "cox" to reply.
That should mean the thermostat is wide open. But the thermostat
could be broken. You can replace it, or hang this one into a pot of
water whose temp is climing. Use a candy thermometer or something
that goes up to 190 to see if the thermostat opens all the way at 180.
I've only done this once, and I don't remember how sure I was that it
was open, or not open, all the way. That is, I didn't know where all
the way was, in practical terms.
Maybe you need a trailer package. Well, just the bigger radiator.
Plus what Dave L said.
Heater cores in many many cars are a pain to replace. Lots of things
on top of them, including parts of your recently added AC, which iiuc
doesn't use rubber hoses, uses metal hoses. Am I right about that?
I've checked it (with infrared thermo gun) quite a few times even
before putting the AC on it and it seems that the car, in cool
weather, runs up to 180 and stays there as it should with a 180
thermo. In hotter weather it would go up to around 190-195 on the
freeway. Now with the AC it's added about 10 degrees but still has a
lower plateau at 180.
I've checked several and a few were bad and would only open about 1/8
inch. Good ones open maybe half an inch.
Since this is an added ac it won't interfere much with the original
heater. Here in AZ it's not unusual for bad heater cores to just be
I did that once. I had a leak, a hose spraying iirc, just as we
arrived outside some Federal building, not a museum, just south of the
Mall in DC. My friend's girfriend worked there and we were picking
her up at the end of the day. She took me down to the engineer's room
and he gave me a piece of pipe 2 or 3" long. Now I probably
couldn't get into the building even if I needed blood.
I guess you need to know how a centrifugal pump works. Pressure rise
across the pump is function of the square of its speed. Double the pump
speed and the delta P across the pump increases 4X. Expansion due to heat
will increase system pressure if it is in a closed system. If a fluid can
expand without being constrained---no significant change in pressure.
It would also matter how hot the water already is.
How old is the car? Is the rad fan. electric?
Thermo. clutch driven with belt?
Or real old car with straight belt driven? No water temp.
gauge on the dash?(very good idea to have one)
How often does that happen? If it is frequent, you have other
problems that need to be fixed. Last time I had a boil over was
probably in the 1960's or so.
This is not the proper thing to do. The engineers have put a lot of
work into getting the right temperature and pressures and you think
you can do a better job? Really?
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