Automotive cooling system pressures
Automotive cooling system pressures
(OP)
I'll start by saying I'm new here, but have found many help full tips over the last two years when searching the net. thanks.
the other day I got to thinking about something that seems simple on the outset but didn't solve out that way. cooling system pressures and rad caps.
rad caps are rated with a pressure relieve, domestic cars are usually in 18~24lbs and imports in bar from 0.9~1.3. now to the question, the cap vents pressure at its listed rating, but is that rating PSIG or PSIA? also once the system is closed is it still subject to external atmospheric pressure?
the reason is I noticed the 0.9 cap on the car and wondered if that's is below atmosphere of 1.0 how does it maintain any pressure to raise the boiling point? goes back to PSIG/PSIA, does it rely on the external air pressure in addition to the spring rating?
oddly I got no answer from Stant when I called the tech dept. it seems like a straight physics question, but with the system closed you can run a vacuum or pressure independent of the external pressure.
the other day I got to thinking about something that seems simple on the outset but didn't solve out that way. cooling system pressures and rad caps.
rad caps are rated with a pressure relieve, domestic cars are usually in 18~24lbs and imports in bar from 0.9~1.3. now to the question, the cap vents pressure at its listed rating, but is that rating PSIG or PSIA? also once the system is closed is it still subject to external atmospheric pressure?
the reason is I noticed the 0.9 cap on the car and wondered if that's is below atmosphere of 1.0 how does it maintain any pressure to raise the boiling point? goes back to PSIG/PSIA, does it rely on the external air pressure in addition to the spring rating?
oddly I got no answer from Stant when I called the tech dept. it seems like a straight physics question, but with the system closed you can run a vacuum or pressure independent of the external pressure.





RE: Automotive cooling system pressures
The 18..24 is psig. The 0.9..1.3 is barg.
Mike Halloran
Pembroke Pines, FL, USA
RE: Automotive cooling system pressures
RE: Automotive cooling system pressures
Reidh
RE: Automotive cooling system pressures
RE: Automotive cooling system pressures
Reidh
RE: Automotive cooling system pressures
The inside can be this much higher than the outside before the relief opens.
It doesn't matter if you measure in g or a, as long as you measure both the same.