7lb vs 13lb radiator cap

[LaGrasta]

I'm running a 13lb cap currently. If I were to switch to a 7lb, what effect does that have on my engine temperatures.

 

[Mercury Mike]

It lowers the boiling point of water in the pressurized system, I think. =) Is 7 LBS the stock for a 170?

 

[fordconvert]

Somewhere I had seen a chart on some site that had pressure vs. mixture for freeze and boiling. Cant find it now, thought it was something like prestone's site but its not there now. Maybe someone else saw it and can remember?

If your problem is leaks lowering the cap pressure is only going to be a minor patch and if you are in a warm climate it may not help at all.

 

[matt1967]

I can't remember how to figure in prestone mix, into the boiling point equasion, but the boiling point is raised 3* per PSI of preassure in system ( determined by cap ).

 

[falcon60]

I'm running a 13lb cap currently. If I were to switch to a 7lb, what effect does that have on my engine temperatures.

If your engine is running at the correct temp with the 13# cap,changing to a 7# won't change a thing. It will make life easier for the hoses and radiator and will work great as long as you have a radiator that will keep the engine temp below the boiling point of the coolant at 7#. I run 4# or 7# caps on all my older cars and have for many years. I always run an overflow (recovery type) bottle and use the sealed cap for that type system.

Terry

 

[matt1967]

I'm running a 13lb cap currently. If I were to switch to a 7lb, what effect does that have on my engine temperatures.

If your engine is running at the correct temp with the 13# cap,changing to a 7# won't change a thing. It will make life easier for the hoses and radiator and will work great as long as you have a radiator that will keep the engine temp below the boiling point of the coolant at 7#. I run 4# or 7# caps on all my older cars and have for many years. I always run an overflow (recovery type) bottle and use the sealed cap for that type system.

Terry

yes it will change, it will change the boiling point of the coolant. 13 PSI is 39* above 212* where as 7# is only 21* above 212*. regardless, unless he overheats 7# will be fine. overheating is when the water boils, so it would overheat at a colder temp.

 

[Anonymous]

I'm running a 13lb cap currently. If I were to switch to a 7lb, what effect does that have on my engine temperatures.

If your engine is running at the correct temp with the 13# cap,changing to a 7# won't change a thing. It will make life easier for the hoses and radiator and will work great as long as you have a radiator that will keep the engine temp below the boiling point of the coolant at 7#. I run 4# or 7# caps on all my older cars and have for many years. I always run an overflow (recovery type) bottle and use the sealed cap for that type system.

Terry

yes it will change, it will change the boiling point of the coolant. 13 PSI is 39* above 212* where as 7# is only 21* above 212*. regardless, unless he overheats 7# will be fine. overheating is when the water boils, so it would overheat at a colder temp.

It won't change a thing because his motor should not be running anywhere near that hot if everything is working properly...

 

[Mercury Mike]

Rogue, it will in fact change the boiling point, regardless of whether it ever boils. But you're right, too. =)

 

[Anonymous]

Rogue, it will in fact change the boiling point, regardless of whether it ever boils. But you're right, too. =)

Of course it will change it, just not to a low enough point that he needs to worry about.

 

[lyonsy]

ratio is 1psi = 1deg centirgrade so whateever that is in your terms

 

[66 Fastback]

Assuming that the cooling system is up to snuff is should not have any noticeable effct. However, there is a possibility that the lowering of the boiling point could have some boiling in localized hot spots. When we think of coolant temp, we are only measureing at one point in the system. Other parts in the system may be quite abit hotter the measured temp.
Doug

 

[Lazy JW]

Assuming that the cooling system is up to snuff is should not have any noticeable effct. However, there is a possibility that the lowering of the boiling point could have some boiling in localized hot spots. When we think of coolant temp, we are only measureing at one point in the system. Other parts in the system may be quite abit hotter the measured temp.
Doug

Yup. There really are some good reasons why they went to higher pressure systems. Spend some time on a 1941 John Deere tractor equipped with thermo-syphon cooling, no water pump, no thermostat and manually controlled radiator shutters on a hot summer day all the while watching the temperature guage.

But no point running any higher pressure than what gets the job done.
Joe

 

[LaGrasta]

my systems cools well. I was only considering the 7lb cap to ease any strain on my lines. I just installed my HVAC system finally and adding the heater core gave me a few leaks (into the interior) until I worked at it a little.

My Dad told me he runs a 7lb cap in his '78 Chevy van in Phoenix and it might do me good to switch.

I think I might add a 7lb and see if all is well. If I run into any overheating problems this coming summer, I can always swap back to teh 13lb. Thanks for all the info.

 

[66 Fastback]

Theoretically with the higher boiling point of the glycol mix, you might be able to get away with atmospheric pressure. However, I once had stationary engines develop holes in the wet sleeve liners. They were natural gas engines, but they failed due to cavitation pitting on the liner. The pits were Honeycombed and went thru the 1/2" thick wall liners. This type of cavitation occurs on stationary nat'l gas and wet sleeve deisel engines. It is a localized attack that occurs on the surface of the liners as the liners vibrate or ring like a bell. I guess the point is that the engines were not overheating with regards to coolant temp. Before it was all said and done, we spent over $100,000 on the engines. The culprit turned out to be a faulty 8 psi radiator cap on the shared cooling system. The additional pressure on the system helps raise the boiling point and prevent the liner cavitation. (None of this is meant to imply that you will see catastrophic failure if you reduce the system pressure. That same failure mechanism does not occur in gasoline car engines. However, it can occur on sume water pumps, but it is not common).
Doug