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Altitude considerations for Liquid cooling

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BrainF,

 

Pressure and temperature (as it relates to auto conversions) are 2 different things. Generally, the two move around hand in hand but not always. Soon after start up you can have a cool rad but a hot block and have high pressure. The thermostat will open, the pressure will drop some but the temp remains the same. Air in the cooling system will also have an effect on pressure independent of temp. In the rotarys there is a possibly of having a cracked side housing that may show as high coolant pressure even though the coolant temp is low.

 

I've always used a 20lb cap on the rotary to lower the boiling point but if the cooling system is working well, you normally don't see temps over 190F. For high altitude work there are a number of factors in the cooling systems favor. The outside temps are lower (you get better heat transfer) and the engine isn't producing sea level power (unless you're blown in some way:cool2: )

 

Dunnknow, neil,

 

I was always under the impression the the cap was a safety valve to prevent the hoses from blowing or blowing off and prevent the inner engine seals from leaking due to high pressue. It does not regulate the pressure created in the cooling system (more than 1 time:sad: ).

 

Air in the cooling system has no function and should not be there as a product of proper bleeding and cooling system construction and design.

 

Any steam that is created should be vented to a lower pressure point (header tank if the heat exchanger is lower than the engine so that the coolant is free from air.

 

 

The rise in pressure is due to the expansion of the liquid due to heat. The pressurization does raise the boiling point. Just don't make your cap blow off point higher than the plumbing can stand or you will loose pressure rapidly.

 

If you have air in the system (between the exit of the pump and the top of the engine block or in a low mounted heat exchanger, you need to get rid of it by purge or redesign. One way to design it out is to have taps at the high points of the engine/heat exchanger with small tubes to the header tank. Any gas formed will then disappear. Gas (steam) has no cooling capacity in our systems.

 

Kinda makes me look at the waterless/pressureless system more closely

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(I was always under the impression the the cap was a safety valve to prevent the hoses from blowing or blowing off and prevent the inner engine seals from leaking due to high pressue. It does not regulate the pressure created in the cooling system)

 

Rich, That too. You are correct, the cap isn't a regulator. I guess I was trying to make the point that pressure does not necessarily follow temperature and it's a good idea to measure both as a diagnostic tool.

 

Neil

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Interesting topic. My observation is that water boils at lower temperatures at higher altitudes. Thus the temp inside the engine is not seeing altitude pressure . The liquid inside the engine sees one atm above sea level pressure because the cap is rated for 14 psi . One atm above see level. The spring in the cap does not care about higher altitudes . It's not going to lift until the internal pressure of the engine reaches above 14 psi. And at higher altitude the outside temperature is colder. If you are running a electric fan on the rad which has a adjustable temp control to keep the engine temp under control . boil over should not be a problem ! And cold should not be a problem either ! Don't know if this was of  any help ? Just thought i would through it out their .

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