Why are car coolant systems pressurised?

[Huntsman]

So know that for every 1 psi of pressure the boiling point goes up 3 degs F.

If the coolant was not pressurised it would be open and hence some might evaporate off, but a condensor could be added easily enough.

So why pressurised?

(I'm not powerfully built with a goatee, neither do I have an MX5)

[ADEuk]

So the coolant doesn't all boil away

[thinfourth2]

Huntsman said:

So know that for every 1 psi of pressure the boiling point goes up 3 degs F.

If the coolant was not pressurised it would be open and hence some might evaporate off, but a condensor could be added easily enough.

So why pressurised?

(I'm not powerfully built with a goatee, neither do I have an MX5)

Your 99% of the way there

So you don't get localised boiling on hot spots

[Mr2Mike]

thinfourth2 said:

Your 99% of the way there

So you don't get localised boiling on hot spots

This is the principal reason, but going back to the OP's suggestion; how would a bulky condenser that requires cooling be a better solution than a small spring loaded cap?

[anonymous-user]

As mentioned, the system operates at a positive pressure above barometric pressure to allow parts of the system to be maintained above the boiling point of the working fluid without loosing said fluid. However another main reason for a pressurised system is to prevent cavitation at the water pump inlet (which is why the header tank is generally connected to the "bottom hose". Without this positive pressure head, the inlet side of the pump will be forced below atmospheric pressure by the pump head, and result in a lot of cavitation, causing low pump efficiencies and possibly even impeller/housing damage.

[anonymous-user]

thinfourth2 said:

Huntsman said:

So know that for every 1 psi of pressure the boiling point goes up 3 degs F.

If the coolant was not pressurised it would be open and hence some might evaporate off, but a condensor could be added easily enough.

So why pressurised?

(I'm not powerfully built with a goatee, neither do I have an MX5)

Your 99% of the way there

So you don't get localised boiling on hot spots

Most modern "precision" cooling systems (i.e. those that use as small a volume of working fluid as possible to reduce the time required for "warmup") use "nucleate boiling" to locally cool areas of the system that have very high heat flux. However, the pressurised system means that this locailise "steam pockets" re-condense (releasing heat) in the cooler zones (such as the radiator). This has proven to be a very efficient way of increasing cooling work.

[drivin_me_nuts]

Slightly O/T. Is there an alternative to water for engine cooling. Of course there are additives, we all use those, but are there liquids used, other than water specifically for cooling engines?

[thinfourth2]

drivin_me_nuts said:

Slightly O/T. Is there an alternative to water for engine cooling. Of course there are additives, we all use those, but are there liquids used, other than water specifically for cooling engines?

Water is pretty much the best coolant around even before you look at the price of the stuff

[davepoth]

Water is absolutely brilliant for cooling - you will remember from school that it has an extremely high specific heat capacity, meaning it takes a lot of heat to warm it up. The only reason people add stuff to it (glycol etc.) is to stop it freezing when it gets very cold.

[Huntsman]

drivin_me_nuts said:

Slightly O/T. Is there an alternative to water for engine cooling. Of course there are additives, we all use those, but are there liquids used, other than water specifically for cooling engines?

I beleive Porsche and VW had some success with an alternative for a while.

[drivin_me_nuts]

thinfourth2 said:

drivin_me_nuts said:

Slightly O/T. Is there an alternative to water for engine cooling. Of course there are additives, we all use those, but are there liquids used, other than water specifically for cooling engines?

Water is pretty much the best coolant around even before you look at the price of the stuff

Well it's certainly cheap compared to chemical products. Are there any instances when for example, the water is cooled other than by a radiator? Something like an a/c cooling unit of some description.

[sebhaque]

drivin_me_nuts said:

Well it's certainly cheap compared to chemical products. Are there any instances when for example, the water is cooled other than by a radiator? Something like an a/c cooling unit of some description.

Slightly o/t but in aerospace, the oil is cooled by the fuel. The exchange is an FCOC (fuel cooled oil cooler).