Cavitation....

I believe but prolly will be corrected if so that's cool. That antifreeze causes cavitation

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Centrifugal pumps would only cavitate if there are large air bubbles circulating in the system. The centrifugal pumps just push fluid at a rate that changes with rpm and flow capability. Now if there is blockage somewhere in the system then they will lose their ability to push fluid depending on how much of the flow track it still passable. Casting sand, wire, and scale from corrosion can cause slow or uneven flow. A radiator that is gooped up & needs rodding out can also slow the flow rate. Head gaskets can also get partially plugged on the smaller holes. It all adds up over time.

Some radiators were never designed to have a pressure cap. All they had was a gasket on the bung. The overflow tube can have a 4 PSI regulator installed that will create the same effect as a pressure cap. Skip has those little do-dads.
 
rotorwrench said:
Some radiators were never designed to have a pressure cap. All they had was a gasket on the bung. The overflow tube can have a 4 PSI regulator installed that will create the same effect as a pressure cap. Skip has those little do-dads.
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I see that Bob Drake sells a 4 lb. cap for a 37 Ford - Part # 78-8100-B. I think that this cap would be preferable to the unit that Skip sells....
 
Not all of the early V8 radiators have a much of a shoulder down inside the filler port. Some have such a small one that a pressure type cap just has nothing to seal against.

If you get one, measure from the top of the opening down to the shoulder area in the filler. Measure the cap for distance from opening seating area to the pressure seal surface and compare them to make sure the seal will have some effect on the shoulder area down inside the radiator opening. If it will have enough length to make contact and compress a bit, it will work. If it is too short for the pressure seal to make contact then it won't. If there is nothing to seal against, it won't

Not all of these supposed pressure caps will work and vendors don't always check them to make sure they will. Ford didn't make a pressure cap till WWII. In 1944 they started offering the 41A-8100 pressure cap for civilian use that was used for 1946 and part of 1947. They went back to the 91A-8100 cap until the 8BA started down the line in 1948 for trucks. All I can say is check it to make sure it works and hopefully it does. If not, just chalk it up to a learning experience and put the Skip's type pressure valve on there.
 
petehoovie said:
Can high flow water pumps cause or contribute to 'cavitation' in a unpressurized cooling system?
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Skips Hi flow pumps are more of a positive drive and do not produce
cavitation. Cavitation is caused by stock pumps with very small or
poorly designed impellers spinning in the coolant which also make
air and air in the coolant reduces heat transfer. G.M..
 
I really don't think the pumps can generate gasses in the coolant where there is none without a reason for it being there. If a block has a head gasket leak and combustion gasses are getting into the water jackets then that can circulate through the system but it will also over pressure the system at some point and purge coolant/gas mix out. Leaks to the outside air will draw air in as well as coolant leaking out. Gasses in the coolant for what ever reason, will make for a terrible heat transfer and eventually the coolant will boil. Air leaks, combustion leaks, and subsequent boiling is the only cause for gasses where there were no gasses to start with.
 
Cavitation is complicated but it will occur at the back of the blades of an impeller if local pressure is reduced below the vapor pressure of the liquid. I doubt if the small diameter impellers on flathead water pumps, high flow or otherwise, can generate that much negative pressure. Maybe at very high RPM? Impeller blade design is a big factor. The hotter the water, the easier it is to cavitate. A pressure cap would reduce cavitation to the extent that pressure in the radiator actually increased.
 
rotorwrench said:
I really don't think the pumps can generate gasses in the coolant where there is none without a reason for it being there. If a block has a head gasket leak and combustion gasses are getting into the water jackets then that can circulate through the system but it will also over pressure the system at some point and purge coolant/gas mix out. Leaks to the outside air will draw air in as well as coolant leaking out. Gasses in the coolant for what ever reason, will make for a terrible heat transfer and eventually the coolant will boil. Air leaks, combustion leaks, and subsequent boiling is the only cause for gasses where there were no gasses to start with.
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What is the milky look, not just clear water if it's not air?? G.M.
 
Milky sounds like oil in the coolant or combustion gasses mixing in which tend to be oily. If a person runs straight water, it can get microbial crap growing in there too. Water wetter or water soluble oil mixed in would be preferable to just straight water.

Back in the late 50s & 60s Ford started putting the radiator so low that the water level was almost even with the top of the engine cooling passages. They used those metal surge tanks connected to the intake manifold to keep the air pocket in the system well above the passages in the block.
 
rotorwrench said:
Milky sounds like oil in the coolant or combustion gasses mixing in which tend to be oily. If a person runs straight water, it can get microbial crap growing in there too. Water wetter or water soluble oil mixed in would be preferable to just straight water.

Back in the late 50s & 60s Ford started putting the radiator so low that the water level was almost even with the top of the engine cooling passages. They used those metal surge tanks connected to the intake manifold to keep the air pocket in the system well above the passages in the block.
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It's not oil or combustion gas, it's air. I did 100's of cooling tests and it's
a well known fact that air in the water cuts down the cooling effect. G.M.
 
Foam or small bubbles of air flowing through the system along with the majority of the coolant is generally not a problem on the older lighter vehicles unless there are leaks somewhere. There is generally not a lot of foaming going on inside there unless there is a cause. When the vehicles started to get larger and heavier after the war then it started to become more problematic due to elevated coolant temperatures from overworked engines. This is why Ford started using the pressure type systems after the war and on. Pressure in the system forces the air pocket to stay in the top of the system where it belongs and still allows for coolant expansion with a higher boiling point. Foaming is almost non existent in a pressurized system unless air or combustion gasses are leaking into it somewhere.

I can't say anything bad about Skip's pumps. There is nothing wrong with increasing the efficiency of the the pump. The older OEM pump impeller designs were adequate for the job under normal conditions. When conditions got outside the normal range is when there is a benefit.

Folks got by for a lot of years with the OEM pumps by knowing the limitations of their trucks or cars and not working them any harder than they had to. When they did have to, they carried a water bag with them.
 
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Folks had problems with over heating, coils getting hot and VL on Flathead
Fords from when they were new. I remember as a kid in the 40's on hot
nights in traffic coming home from the Jersey shore stalling over heating
and fooling around maybe 1/2 hour to get it started. Everyone carried a
spare coil, fuel pump and a bottle for water. G.M.
 
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