When a cooling-systems designer is deciding on the
overflow bottle design, what makes them choose to
make a simple overflow like in the MINI Cooper or
a pressurized overflow like the MCS?

Now you can tell me that the MCS has an intercooler,
but I believe that the intercooler is air-to-air, and doesn't
interact with the engine coolant.

Is the difference between 115 and 165 (or whatever)
horsepower the trigger? Do ALL engines larger than
100 HP have pressurized overflow bottles?

And why did my 1988 VW Quantum/Synchro Wagon
5-cylinder have a pressurized overflow?

 

A pressurized system actually keeps the engine temperature a
few degrees cooler. The supercharger causes the engine to run
a few degrees hotter.
I think in other cars there are other factors involved. I had a
mid-engine car that had a pressurized system in the past. i
think the pressure sytem ensures the radiator stays full at all
times. Good question. Other 'techies' probably will have a
better explaination. Stay cool!

 

Both the MINI Cooper and the MCS have pressurized cooling systems.
It's just the overflow bottle on the MINI Cooper that is not pressurized.

It sits at the end of a hose, and if the main cooling system gets too much
pressure from the expanding coolant, it forces a little bit up the tube through
a pressure relief valve into the coolant overflow bottle.

When it cools off and the coolant contracts, it sucks a little coolant out
of the overflow bottle.

So both systema have the amin cooling system pressurized, and the radiator
stays full on botn, but on the MCS, the overflow bottle is a part of the main
pressurized cooling system, abnd that's why the bottles blow apart.

 

Trippy,

thanks for the explanation. i'm considering an aftermarket overflow canister to dress up the engine bay. will changing the coolant overflow canister create problems because the cooper s system is pressurized? Eg, would there need to be a pressure-relief fitting on the tank?

i don't know much about coolant issues so any help is much appreciated.