radiator caps, cooling system pressure

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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". http://www.mishimoto.com/mishimoto-high-pressure-radiator-cap-13-bar.html 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?????
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Ashton Crusher wrote:

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 can spring a leak.
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AMEN!
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On Apr 21, 9:50 pm, " snipped-for-privacy@sbcglobal.net"

DONT EVEN THINK ABOUT THIS WITH A CHEVY VENTURE! their engine the 6 cyc one tends to develop super expensive head gasket leaks as is......
some things are best left alone
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wrote:

wouldn't overpressure ANY system.
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On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), " snipped-for-privacy@sbcglobal.net"

water from one side of the pump to the other. Expansion due to heat is what builds pressure..
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On Apr 21, 11:15 pm, snipped-for-privacy@snyder.on.ca 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.
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On Mon, 22 Apr 2013 05:29:32 -0700 (PDT), " snipped-for-privacy@optonline.net"

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.
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Ashton,

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.
Dave M.
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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.
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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. MLD
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On Mon, 22 Apr 2013 19:40:05 -0400, "David L. Martel"

expensive cooling system repairs in your future. If you are worried, which you should not be, put on an electric fan in front of the rad/condensor.
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On 4/22/2013 8:51 PM, snipped-for-privacy@snyder.on.ca wrote:

My 1965 Dodge Dart used a 13psi radiator cap on the good old Slant Six radiator, at least that's what the part look up states. o_O
TDD
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On 04/22/2013 02:42 PM, Ashton Crusher wrote:

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 cools down.
good luck
nate
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wrote:

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?
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wrote:

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 bypassed :-)
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wrote:

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.
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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. MLD
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MLD wrote:

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)
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wrote:

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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