radiator caps, cooling system pressure

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On Thursday, May 1, 2014 11:06:58 PM UTC-4, snipped-for-privacy@snyder.on.ca wrote:

It will cause a pressure increase on the output side of the pump versus in the input side.
The increased pressure increases the boiling point of the

I don't believe that's true. If you measured the system pressure with respect to the atmosphere right at the pump output, it should be higher than the pressure measured similarly at the pump input. Both those points would rise or fall with the temperature of the coolant.

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On 5/1/2014 7:05 PM, mike wrote: ...

Fluid flowing or static? (Yes, it makes a difference.) The static pressure of a stagnant system would be uniform and steady, yes.

Nonense. The pump performs work on the fluid and while one doesn't lose fluid in a well-maintained automotive cooling system, it is not a constant volume system, it does have expansion volume thru the overflow and even water isn't totally incompressible and pressure does go up.

Pump principles are principles... There's this thing about "principles"--if they don't apply, then they aren't. :)

Nonsense, while running (and the thermostat open) it's circulating the water. It performs mechanical work on the fluid raising the output pressure in the process which it _must_ do in order to overcome the flow restrictions and pressure drops along the way before it gets back to the pump inlet again. Of course the physics of it is that the pump doesn't "create" pressure--it imparts kinetic energy from the impellers to the fluid to create velocity therein. It is the resistance to flow that creates the measured pressure even though it is commonly referred to "increasing (pressure) head".
The pressure is a variable value from a maximum at the pump outlet to a minimum at the pump inlet. The pressure at the radiator cap will be something under the 12 psi or so of the cap release spring or else it would lift.
So, while your statement above about the closed system and no water isn't right, the idea that a pump doesn't "create" pressure is correct; but the pressure is higher at the pump outlet as compared to the inlet because the input kinetic energy and output velocity thus imparted are reflected in a higher pressure owing to the design of the pump volutes. If didn't have a higher pressure at that point, then there'd be no driving force sufficient to get through the other downstream flow restrictions. It's analogous to needing voltage to "push" a current thru a load.
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wrote:

As the engine temperature rises, tiny gas bubbles start to form on the walls of the cooling cavities. The liquid changing to gas causes the pressure to increase. When the fluid is cold, the bubbles are condensed back into liquid right away and there is little pressure increase. As the coolant temp rises, it takes longer for them to condense, the volume of gas increases and the pressure increases.

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On 4/30/2014 6:15 PM, MLD wrote:

...

What the limit is of how much pressure the water pump can produce is based on the pump design and I really don't know what those values typically might be. But, the pressure in the system is controlled by the pressure cap. There's a very good description at the following link...
<http://books.google.com/books?id=xLxySLNAe3YC&pg=PA136&lpg=PA136&
dq=does+radiator+cap+control+radiator+pressure&source=bl&ots=--_LIFglKt&
sig=vhm95_RJG8vWT6iJMsaY-3OAGmM&hl=en&sa=X&eiýNjU-SuJfP7yAGho4CwCQ&
ved IgBEOgBMAg#v=onepage&
q=does%20radiator%20cap%20control%20radiator%20pressure&fúlse>
--


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30 psi is putting it mildly....
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wrote:

in pressure across the radiator. Suction on one side, pressure on the other. A matter of a few psi with a good rad and the thermostat open. The pump is not capable of producing very high pressures.. The pressure on the low side can be up to 5 psi below nominal, and on the high side as much as 5psi above no
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no head pressure. A good water pump may produce a 5 psi head, and draw an equivalent depression on the low side of the pump for a maximum pressure differential of 10psi - but that is a "blueprinted" pump at optimal speed with an adequately restrictive radiator.
Real world numbers are generally quite significantly less. Measured 3psi on BMW 328 just this week at 3000 RPM. Above and below 3000 it dropped off. That was with diluted coolant (about 20-25% glycol) due to having just repaired a leak and having the normal "fun" bleeding all the air out of the nasty little Kraut!!
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Having performed thousands of automotive cooling system flow/pressure and pump performance tests, I can say you have no idea, either.
Without getting into particulars, recently....5500 pump RPM...10 psi at the pump inlet, 200+ GPM into the block at 80 PSI pump outlet pressure
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Your comment makes no sense to me. There is always water at the inlet to the pump if the system if full of water. You can see the water moving if you take the cap off, at least on some systems where it opens into the tank. Clearly the pump is pumping water, therefore it's getting some to pump and it's certainly not as vapor.
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On Fri, 02 May 2014 14:49:18 -0400, snipped-for-privacy@snyder.on.ca wrote:

Where in the system did you take that 3 psi measurement at?
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On Fri, 02 May 2014 14:43:15 -0400, snipped-for-privacy@snyder.on.ca wrote:

My little 1.5 hp swimming pool pump, with similar sized centrifugal impeller to a car, similar sized pipes as a radiator hose, and running at a couple thousand rpm can easily produce over 25 psi if you shut down the outlet valve. It seems likely to me that the water pump in a 150 hp car could do the same if the flow was restricted.
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wrote:

MLD, do you know where to find a flow rate vs RPM curve for any common stock water pumps? I'm surprised I can't seem to find anything mfr spec curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.
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wrote:

MLD, do you know where to find a flow rate vs RPM curve for any common stock water pumps? I'm surprised I can't seem to find anything mfr spec curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.
Found this Flow vs Delta P characteristic. http://www.bing.com/images/search?q=auto+water+pump+flow+curve&qpvt=auto+water+pump+flow+curve&FORM=IGRE
MLD
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On Tue, 13 May 2014 15:15:49 -0800, "Guv Bob"

I was looking to see what I could find on water pumps and didn't find much. I did come across this http://teae.org/cooling-the-tiger/ which is pretty interesting though. A bunch of home experiments looking at what things make for better cooling.
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wrote:

mfr spec curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.

Thanks, that's very interesting info. I'm not familiar with the particular car they are doing the testing with, but it seems odd to me that they consider coolant temps below 212 deg F as normal. They must be water with no glycol in a system open to atmosphere. However, I didn't read it that closely thought so (as most people say) I may be off.
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On Thursday, May 15, 2014 2:41:20 AM UTC-4, Guv Bob wrote:

curves at the various mfrs and parts houses. Doesn't matter what mfr or ve hicle -- just any common street car single head pump.

nsider coolant temps below 212 deg F as normal. They must be water with no glycol in a system open to atmosphere. However, I didn't read it that clo sely thought so (as most people say) I may be off.
Why does normal coolant temp below 212F equate to using pure water and a system open to the atmosphere? It can be lower, depending on factors like the thermostat and where the coolant temp is being measured. It just can't be higher than 212F.
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On Wed, 14 May 2014 23:43:00 -0800, "Guv Bob"

the BP of the pressurized mixture is exceded. Normal Operating Temp is closer to 195F-215F
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wrote:

mfr spec curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.

- Thanks, that's very interesting info. I'm not familiar with the particular car they - are doing the testing with, but it seems odd to me that they consider coolant - temps below 212 deg F as normal. They must be water with no glycol in a - system open to atmosphere. However, I didn't read it that closely thought so - (as most people say) I may be off.

Probably a good point, but I'm not sure I understand what you mean.
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On Thursday, May 15, 2014 12:54:31 PM UTC-4, Guv Bob wrote:

c curves at the various mfrs and parts houses. Doesn't matter what mfr or vehicle -- just any common street car single head pump.

Maybe I don't understand what you mean. You said:
"but it seems odd to me that they consider coolant temps below 212 deg F as normal. They must be water with no glycol in a system open to atmosphere. "
A normal mix of water and antifreeze won't boil below 212F. You could run the car all day at 205F, no? It's the opposite that's the problem. You can't run a water only coolant, open air, above 212F. I would think temps below 212F would be normal, depending on the thermostat, operating conditions and again where the temp is measured.
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wrote:

uto+water+pump+flow+curve&FORM=IGRE

Thanks. Still looking for RPM vs Floweret
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