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In my search for radiator caps and recommended pressure(spurned on by another thread), 54-56 I find 7# to be the recommended release pressure.  57 on up 15# is recommended.  Can a 15# cap be used for a 54-56 application? Is anyone running a 15# cap on s 54-56?  15# or less radiator cap?

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15 hours ago, avgwarhawk said:

Can a 15# cap be used for a 54-56 application?

If it fits.  Your 7# radiator has narrower notches in the filler neck and a higher pressure cap will not usually fit.  The 13# cap from my factory A/C cars will not fit on my non-A/C convertible.

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2 hours ago, buick5563 said:

I didn’t think about the fact that I have AC radiators in both of my 55’s @avgwarhawk def check first, BUT I had a 7 on both cars and then swapped em and they fit fine. 

 

Why did you switch to the 15/16# cap.  Better cooling? 

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45 minutes ago, Ben Bruce aka First Born said:

The ONLY thing a higher pressure cap will do is ALLOW the coolant to get hotter before boiling.  Will not heat or cool better or worse.  A higher pressure MIGHT cause a leak if there are weak spots in the system.

 

  Ben

 

 

Ben, I was reading up on caps, boiling points, etc.  Wondering why 7# seems to be the cap for cars in the 40's and early 50's. Some cars beyond that.  Thanks for the info.      

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2 hours ago, avgwarhawk said:

 

 

Ben, I was reading up on caps, boiling points, etc.  Wondering why 7# seems to be the cap for cars in the 40's and early 50's. Some cars beyond that.  Thanks for the info.      

 

 Engine design and advancements.  Engine builders discovered that engine ran better and more efficiently at higher temps. Most, if not all, today are running 200.

    A diesel mechanic told me , in the early '70s,  that they ran much better at 200 but the builders set at 180 as they were afraid the drivers would not watch the temp as closely as they should.

 

  I have a 195 thermostat in my 1950.

 

  Ben

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32 minutes ago, Ben Bruce aka First Born said:

 

 Engine design and advancements.  Engine builders discovered that engine ran better and more efficiently at higher temps. Most, if not all, today are running 200.

    A diesel mechanic told me , in the early '70s,  that they ran much better at 200 but the builders set at 180 as they were afraid the drivers would not watch the temp as closely as they should.

 

  I have a 195 thermostat in my 1950.

 

  Ben

Very true. Hot engine better burn.  I believe I have a 180 in the 54.  

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Our '51 GMC pickups had a "pressure bulb" in the radiator and a very low pressure/plain radiator cap.  As mentioned, the modest pressure increases would allow the engines, which were beginning to see factory a/c installations, didn't puke with the pressure caps, as readily.  With thermostats below 180 degrees, Vic Edelbrock claimed that engine wear would increase.  But hot rodders always gravitated toward the cooler thermostats as a cold engine allegedly makes more power.  At least "back then".

 

FWIW,

NTX5467

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When I was younger I thought it was better to have my engine run cool. I took out the thermostat then I ran a 160. I was basically trying to mask the real reasons the car was running hot. Either bad tuning or blocked radiator. As I got older and I discovered why certain things worked together to be efficient, I raised the thermostat to 180 and installed higher caps. Both of my cars have AC, so I may have blindly installed the 13-16lb caps but I ran a 7 on the factory AC Special for a long time and it only puked a little when it was really hot. I don’t even think I realized it was the lower pressure cap until it looked a little funky and I was going for a senior preservation and was detailing under the hood. At that time I installed a 13. 

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One of my cars still has a 160* thermostat which means I 'have to' drive it an extra 20 miles to be sure everything is warmed up enough.;)

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12 hours ago, old-tank said:

One of my cars still has a 160* thermostat which means I 'have to' drive it an extra 20 miles to be sure everything is warmed up enough.;)

 

Which ALSO means it takes even MORE miles to get the oil temp up enough to cook out all of the nasty stuff!

 

Enjoy!

NTX5467

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Base line we all know that water boils at 212 F.   Not complicating the fact with altitude, additives, etc.

for every 1 lb of pressure the water is under,  the boiling point increases 3 deg F

So the early cars with 7 psi pressure caps would see a 21 degree boiling point increase (to 233 F)

in that case roughly a 10% increase of the boiling point. 

As noted above....the extra pressure can cause weak links to fail.... ie  water pump seals,  hoses,  etc

I suspect all of that was looked at when pressurized systems were introduced in 1940  but if you are

going to a higher psi pressure cap you might want to do some testing before taking a road trip.

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 I realize most of us know, but for those that do not:

   

  Thermostat temp  specs do not  make a car overheat, they only assure the coolant runs no cooler.  

 

  A higher pressure cap will not CAUSE higher temp/pressure, only allow the pressure to become higher before the coolant boils.

 

  Ben

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One thing I came across years ago was that the stated temp of the thermostat is the OPENNING temp of the item, although if everything is working as it should, that can also become the operating temp of the engine.  The thermostat is a calibrated restriction of coolant flow such that it does not move through the engine too fast.  If the coolant moves too fast, turbulence around the individual cylinders can become too great and reduce heat absorption by the coolant, which can increase the possibility of undesirable hot spots within the cylinder block and/or cylinder heads.  In effect, reduced efficiency.

 

Many dirt track racers will not use a thermostat, but a big washer with a center hole size to give them the engine temps during the race that they desire.  Cylinder head gaskets usually have water passage restrictor holes in them.  Should those holes enlarge with "wear", the water flow can become too fast for good head absorption by the coolant.  In their purpose-built vehicles, the cooling systems are designed around the intended use of the vehicle and the particular chassis/body design, so seeking to mimic what they do for a street-driven vehicle might not be advisable.

 

over the decades, I've heard of people who had an overheat situation, stopping to remove the thermostat, which helped "cure" the situation enough that they could continue their journey, but we never heard of what the real cause of the overheat situation really was.  If it was a failed thermostat that was stuck closed or something else in the cooling system that needed attention?  BTAIM

 

Rest assured, though, that IF GM could have designed a cooling system that would work in ALL situations and not need a thermostat, they would have done it on an internal combustion engine.  

 

Normal water at sea level will boil at 212 degrees F.  Less with increasing altitude.  But with a 15psi radiator cap, that boiling point can be increased to 260 degrees F.    Remember, too, that that temp is at the radiator or thermostat housing, which is probably a bit lower than the temp at the engine's main bearings or piston pins!  Most modern motor oils have a flash point of over 400 degrees F.

 

Enjoy!

NTX5467

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