On a pressurized cooling system with a 14lb radiator cap, under normal operating conditions should the system pressure ever exceed the 14lb rating of the cap? if not, what maintains the system pressure under the 14lb popping pressure of the radiator cap. I ask this question due to a problem I am experiencing with a cooling system.Bill M.
- Thread starter bill mart
- Start date
BushogPapa
Well-known Member
Seems to me that the 14 lb of pressure if to keep the coolant from boiling and causing hot spots in the head..most likely around the exhaust ports..
Under normal conditions, I don't think there should be any venting..excepting, if there is not sufficient room for fluid expansion..
If you put too much in, there will be some over-flow the first time or two you heat the system up..
Ron.
BushogPapa
Well-known Member
Seems to me that the 14 lb of pressure if to keep the coolant from boiling and causing hot spots in the head..most likely around the exhaust ports..( raises Boiling point of coolant)..
Under normal conditions, I don't think there should be any venting..excepting, if there is not sufficient room for fluid expansion..
If you put too much in, there will be some over-flow the first time or two you heat the system up..
Ron.
No. Nothing regulates the pressure. The cap is more a safety valve.
The thermostat is set to a specific tempeture. If the system exceeds the tempeture, the cap provides a release. The reason for the pressure cap is to prevent the hoses from blowing. The system tempeture to some extent determines the pressure rating for the cap. Water boils at 212F normally. At 5psi it may be up around 225F. At 10 its like 250F.
So if you are GM and want the engine to run at 210F under normal conditions, you need the additional tempeture surge room (normal fluctuations caused while driving). By using a cap that rated at 10psi, you can spike the temp to 250F without it boiling over.
Down side is when it goes, it really blows. As the pressure has gone away, All the water in the system boils almost instantly.
Keep in mind this is for a properly operating system. If you have a compression leak, the system would eventually build up enough pressure to cause it to pop.
The thermostat is set to a specific tempeture. If the system exceeds the tempeture, the cap provides a release. The reason for the pressure cap is to prevent the hoses from blowing. The system tempeture to some extent determines the pressure rating for the cap. Water boils at 212F normally. At 5psi it may be up around 225F. At 10 its like 250F.
So if you are GM and want the engine to run at 210F under normal conditions, you need the additional tempeture surge room (normal fluctuations caused while driving). By using a cap that rated at 10psi, you can spike the temp to 250F without it boiling over.
Down side is when it goes, it really blows. As the pressure has gone away, All the water in the system boils almost instantly.
Keep in mind this is for a properly operating system. If you have a compression leak, the system would eventually build up enough pressure to cause it to pop.
rlp in Co.
Well-known Member
What is the problem? Maybe someone can help.
when cold and a system without an expansion tank or one with low coolant level.. with engine running you should only see the water flow.. if you see bubbles ya got a compression leak.
If you are loosing coolant and do have an expansion tank may be it is too low.
sometimes when you fill radiator all seems good, but if the top hose isn't full and can happen as most of the newer cars flows up hill creating an air bubble. the only way to check this system is at the expansion tank when at normal operating temp.
If you are loosing coolant and do have an expansion tank may be it is too low.
sometimes when you fill radiator all seems good, but if the top hose isn't full and can happen as most of the newer cars flows up hill creating an air bubble. the only way to check this system is at the expansion tank when at normal operating temp.
MarkB_MI
Well-known Member
- Location
- Motown USA
The cooling system pressure is the vapor pressure exerted by the hot coolant. For pure water, the vapor pressure at 212F equals sea level atmospheric pressure, which is why water boils at 212F. Pressurizing the cooling system allows the vapor pressure to rise above atmospheric pressure, up to the point where the VP exceeds atmospheric pressure plus the radiator cap pressure. At that point, the coolant will boil.
How about explaining your problem?
How about explaining your problem?
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