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radiator caps, cooling system pressure



 
 
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  #11  
Old April 22nd 13, 04:19 PM posted to rec.autos.misc,alt.home.repair
MLD
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Posts: 74
Default radiator caps, cooling system pressure


"Ashton Crusher" > wrote in message
news
>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-h...ap-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?????


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.
MLD

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  #12  
Old April 22nd 13, 04:57 PM posted to rec.autos.misc,alt.home.repair
harry
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Posts: 106
Default radiator caps, cooling system pressure

Thoughts?????

One other possibility is you may have a blown head gasket.
  #13  
Old April 22nd 13, 06:07 PM posted to rec.autos.misc,alt.home.repair
[email protected][_2_]
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Default radiator caps, cooling system pressure

On Apr 22, 11:57*am, harry > wrote:
> Thoughts?????
>
> One other possibility is you may have a blown head gasket.


The other very real possibility is that harry is the village idiot,
as has been proven time and time again.
  #14  
Old April 22nd 13, 07:10 PM posted to rec.autos.misc,alt.home.repair
[email protected]
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Posts: 931
Default radiator caps, cooling system pressure

On Sun, 21 Apr 2013 23:31:02 -0700 (PDT), harry
> wrote:

>On Apr 21, 11:21*pm, Ashton Crusher > wrote:
>> 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-h...tor-cap-13-bar....
>> 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?????

>
>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.


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.
>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.


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..

  #15  
Old April 22nd 13, 07:13 PM posted to rec.autos.misc,alt.home.repair
[email protected]
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Posts: 931
Default radiator caps, cooling system pressure

On Mon, 22 Apr 2013 08:57:20 -0700 (PDT), harry
> wrote:

>Thoughts?????
>
>One other possibility is you may have a blown head gasket.

Which WILL cause the pressure to increase rapidly if it is causing an
overheating problem - and even a 30psi cap would vent under these
conditions
  #16  
Old April 22nd 13, 07:42 PM posted to rec.autos.misc,alt.home.repair
Ashton Crusher[_2_]
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Posts: 2,874
Default radiator caps, cooling system pressure

On Mon, 22 Apr 2013 05:29:32 -0700 (PDT), "
> wrote:

>On Apr 21, 11:15*pm, wrote:
>> On Sun, 21 Apr 2013 18:50:29 -0700 (PDT), "
>>
>>
>>
>>
>>
>> > wrote:
>> >On Apr 21, 6:11*pm, Tony Hwang > wrote:
>> >> Ashton Crusher wrote:
>> >> > 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-h...tor-cap-13-bar....
>> >> > 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 additioingnal 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?????

>>
>> >> Hi.
>> >> 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.- Hide quoted text -

>>
>> >> - Show quoted text -

>>
>> >AMEN!

>>
>> *A water pump cannot produce system pressure because it just moves
>> water from one side of the pump to the other. Expansion due to heat is
>> what builds pressure..- Hide quoted text -
>>
>> - Show quoted text -

>
>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.


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.
  #17  
Old April 22nd 13, 07:44 PM posted to rec.autos.misc,alt.home.repair
Ashton Crusher[_2_]
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Posts: 2,874
Default radiator caps, cooling system pressure

On Sun, 21 Apr 2013 22:40:35 -0400, Ed Pawlowski > wrote:

>On Sun, 21 Apr 2013 15:21:32 -0700, Ashton Crusher >
>wrote:
>
>>I was thinking of putting a higher pressure cap on one of my cars to
>>increase the factor of safety against boiling.

>
>
>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?


It would just change it to the pressure for AC cars. For it's first
52 years of use it was without AC. I added AC to it.
  #18  
Old April 22nd 13, 07:50 PM posted to rec.autos.misc,alt.home.repair
Ashton Crusher[_2_]
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Posts: 2,874
Default radiator caps, cooling system pressure

On Mon, 22 Apr 2013 08:57:20 -0700 (PDT), harry
> wrote:

>Thoughts?????
>
>One other possibility is you may have a blown head gasket.


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
up.
  #19  
Old April 23rd 13, 12:40 AM posted to rec.autos.misc,alt.home.repair
David L. Martel[_2_]
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Posts: 10
Default radiator caps, cooling system pressure

Ashton,


> 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.


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.


  #20  
Old April 23rd 13, 01:17 AM posted to rec.autos.misc,alt.home.repair
Ashton Crusher[_2_]
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Posts: 2,874
Default radiator caps, cooling system pressure

On Mon, 22 Apr 2013 19:40:05 -0400, "David L. Martel"
> wrote:

>Ashton,
>
>
>> 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.

>
> 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.
>


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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