Water pump cavitation. Modifying impeller

[Jim/GA]

Sturgis and Eagle are right. Basic Physics.
In a closed system, a restriction will slow the supply to the water pump and it can't possibly pump too much too quick. Then the motor can overheat and cause the water in the block to boil. That will create air in the system which will force water and air out the overflow. The restriction that causes this result is usually a plugged radiator. In fact it is the only unit in the system that can plug up.

I agree. With the waterpump on the outlet of a Model A engine (compared to on the cold water inlet on a modern car) you have the pump sucking on hot water, near the boiling point. Pull too hard at the impeller (spin it at high RPM, like at 45 MPH) and you make that hot water flash to steam, especially if the radiator has any restriction.

Water that turns to steam (not air, Luke) has a 1700 times increase in volume! (My wife teaches HS chemistry and just figured that out for me.) As Cool Hand noted, this rapid increase in volume in the cooling system raises the liquid level in the upper tank and liquid coolant spills out on the ground. The steam also vents out the overflow but you don't see it. One way or another, you are losing coolant and you are running hot.

Get some coolant actually boiling in the block, not at the impeller but somewhere in the block at a hot spot, and you REALLY start creating some large volumes of steam and out goes your coolant. That's when you see your engine boiling over.

So people who have reported success with grinding the impeller down or drilling holes in the blades on it are reducing the flash of hot water to steam at the impeller. I can see where that would help, if your radiator was "good enough". If it is too plugged up, even that won't help and you need a new radiator that flows better.

 

[Jason in TX]

You guys keep saying "closed system." Model As do not have a closed cooling system. ...overflow tube.... Radiator cap that blows rusty water all over your windsheild.... ...lack of a pressurized radiator cap....

It is a balanced system. The instructions even suggest that the original impellers are matched to the cooling capacity of the original radiator, but not matched to the modern radiators.

Your Old style pump can pull the water out of the engine, overflow the top tank of your new radiator, run out the overflow tube and onto the ground. The pump impellers are not matched to the newer radiator technology.




So my brand new modern radiator core that could cool a big block chevy (not clogged) and my brand new leakless waterpump that was pumping all the water out onto the ground should NOT have been ground down like the instructions suggest in the box because it's a closed system and it must be something else? But I'm running between 170 and 190 now.



...

 

[CarlG]

What I don't understand is that I can blow water / steam out the overflow and/or cap (if not sealed real well) when accelerating up a grade, but the temp gauge still shows +/- 180. If it's boiling or making steam, shouldn't the gauge read over 212?

 

[Jim/GA]

What I don't understand is that I can blow water / steam out the overflow and/or cap (if not sealed real well) when accelerating up a grade, but the temp gauge still shows +/- 180. If it's boiling or making steam, shouldn't the gauge read over 212?

The temp gauge is giving you the average temperature of what actually flows by it. Is your temp bulb inserted along the top of the upper hose? Or in the side of the upper hose (like mine is)?

If the steam is created down in the block or at the impeller and then flows along the top of the upper hose, the steam does not touch the temp bulb.

 

[CarlG]

My temp gauge probe is mounted in the Vintage Precision thermostat block, which puts it directly between the water pump and the upper hose.

 

[Cool Hand Lurker]

"Your Old style pump can pull the water out of the engine, overflow the top tank of your new radiator, run out the overflow tube and onto the ground. The pump impellers are not matched to the newer radiator technology."

A pump can't pull water out of the engine unless something goes in to take up the space where the water used to be. That has to be water or air. (steam fits into my broad definition of air in this application). So the water has to be at boiling temp and converted to steam (air) or it won't come out. The only exception would be if the radiator hoses are long and flexible enough to collapse under the vacumm pull of the pump.
At normal operating temps, the only water that the pump can move is water that comes from the radiator. So the radiator flow will regulate the maximum flow. Radiator efficiency determines radiator cooling capacity.
Radiator flow equals water pump flow. New or old radiator, new or old pump.... doesn't matter.

 

[RonC]

Carl, just because your loosing water doesn’t mean your car is overheating. A poor cap gasket, missing baffle plate or too much water in the radiator to start with will allow water to spew out as it expands under load.

 

[CarlG]

Thanks Ron, I needed that! Makes me feel much better!

 

[29restorod]

I spent 8 years of my career testing cooling system components for AMC,Jeep,Chrysler. I was just asking about the caracteristics of the leakless pump. I agree,that most likely I have a plugged radiator,and that may be the cause of the cavitation. I am sure that the rad in the car now is not a modern replacement. The car had seen almost no use since 1999,and the rad is full off nicks,and scrapes. I notice there is grease in the top tank. I got a new cap gasket today from Snyders,and it is too thin. My next order from them will have an "O" ring. After I finish installing my Stromberg 97 carb. I will remove rad and try cleaning it with Draino.

 

[mach0415]

All these hole are doing is slowing down the flow which is the wrong direction. The water is just getting hotter. Removing a part of the blade is doing the same thing, You want the coolant to flow as fast as it can through the system. The heat transfer is a function of the temperature difference. The cooler the coolant the larger heat transfer from the block.

In theory this sounds correct, but slowing the coolant flow slightly causes a more efficient heat transfer, if the radiator is good. With heat transfer at maximum efficiency, then the liquid is cooled in the radiator more effectively as it is exposed to cooler flues/fins over a longer duration - especially in an A radiator.

In the late 1990s, Ford had issues with multiple vehicle lines, regarding low HVAC heat output in the winter. The solution that cured the problem was to put a restricter orifice inline to the heater core to slow down flow for more efficient heat transfer.

 

[Chris in WNC]

EVERY Model A overheating problem I've had in 26 years has been cured by a complete professional cleaning of (or replacement of) the radiator.

leave the water pump be.

 

[steve s]

In theory this sounds correct, but slowing the coolant flow slightly causes a more efficient heat transfer, if the radiator is good. With heat transfer at maximum efficiency, then the liquid is cooled in the radiator more effectively as it is exposed to cooler flues/fins over a longer duration - especially in an A radiator.

In the late 1990s, Ford had issues with multiple vehicle lines, regarding low HVAC heat output in the winter. The solution that cured the problem was to put a restricter orifice inline to the heater core to slow down flow for more efficient heat transfer.

This first bit of lore has always fascinated me. How can we ignore the fact that while some coolant is taking a leisurely trip through the radiator so more of its heat can be removed, the rest of the coolant is taking an equally leisurely trip through the motor, where it will absorb even more heat that will soon need to be removed?

I am even more perplexed by the second statement: Surely, the amount of heat coming off of a heater core will be greater the hotter the coolant in it is. I understand that Ford engineers are good, but can they really reverse some laws of physics, I wonder.

Steve

 

[mach0415]

This first bit of lore has always fascinated me. How can we ignore the fact that while some coolant is taking a leisurely trip through the radiator so more of its heat can be removed, the rest of the coolant is taking an equally leisurely trip through the motor, where it will absorb even more heat that will soon need to be removed?

I am even more perplexed by the second statement: Surely, the amount of heat coming off of a heater core will be greater the hotter the coolant in it is. I understand that Ford engineers are good, but can they really reverse some laws of physics, I wonder.

Steve

I would think that if it were lore, Ford wouldn't have spent valuable time and resources doing it, and actually solving the original concern. Had I not become a Ford Master Tech and witnessed the fact that it actually solved the problem, I would not have stuck my neck out to risk the workings of ignorance. But that's beside the point.

You are mistaken. There is no "leisurely" stroll of coolant. We are not creating a restriction, entirely. There is just decreased flow from the pump. A thermostat stuck in the closed position is a restriction, resulting in overheat.

Given the surface area of an A radiator, as well as the volume of coolant, the coolant temperature can be lowered even more, by exposing it longer to an air-to-liquid heat transferable material (i.e. radiator), resulting in increased efficiency (The same is true for a heater core.) thereby removing even more heat from the block. There is a lot of real estate in an A radiator, so I could see this to be true IF for some reason another head posed water pump clearance issues.

Did I read over at the T section that some came with OPTIONAL water pumps?

 

[pooch]

212 F is the boiling point of water at atmospheric pressure.

A model A with a "sucker" type pump reduces the water pressure which lowers the boiling point, so your gauge is reading low, but it is boiling.

Modern systems running pressure caps and pusher pumps raise the BP to about 230F.

 

[Jim/GA]

212 F is the boiling point of water at atmospheric pressure.

A model A with a "sucker" type pump reduces the water pressure which lowers the boiling point, so your gauge is reading low, but it is boiling.

Modern systems running pressure caps and pusher pumps raise the BP to about 230F.

You are correct. My wife (in her Chemistry class) puts a beaker of water in a big glass vacuum bell and hooks a vacuum pump up to it. As she draws the pressure down in the bell, you can see the water in the beaker begin to "boil" (turn to water vapor). That water is not 212 degrees, it is at room temperature. You are not getting this extreme pressure reduction in your engine, but the concept is the same.

Any hot water that is close to the boiling point can be made to boil by pulling the pressure down on it, due to the waterpump trying to pull hot water out of the top of the engine faster than the radiator core will let cool water flow in.

Modifying the impeller to have it pull less volume of water out would reduce the pressure reduction and reduce the amount of water that is flashing to vapor when you have a radiator that is not too plugged up. But if the radiator is really restricted, even reducing the flow by modifying the impeller won't make up for it.

 

[Jim/GA]

"Your Old style pump can pull the water out of the engine, overflow the top tank of your new radiator, run out the overflow tube and onto the ground. The pump impellers are not matched to the newer radiator technology."

A pump can't pull water out of the engine unless something goes in to take up the space where the water used to be. That has to be water or air. (steam fits into my broad definition of air in this application). So the water has to be at boiling temp and converted to steam (air) or it won't come out. The only exception would be if the radiator hoses are long and flexible enough to collapse under the vacumm pull of the pump.
At normal operating temps, the only water that the pump can move is water that comes from the radiator. So the radiator flow will regulate the maximum flow. Radiator efficiency determines radiator cooling capacity.
Radiator flow equals water pump flow. New or old radiator, new or old pump.... doesn't matter.

I agree, Cool Hand. Here's an idea for an experiment. If you think you might have a plugged radiator that can not supply water to the engine as fast as the water pump is trying to pull it out the top (at high RPM):

What if you open the drain petcock for a few seconds while the engine is running (stationary in your drive) at high RPM?

If the theory is that water can not flow out of the radiator fast enough to replace what the water pump is trying to pull out, then AIR should get sucked into the petcock in the lower pipe, instead of water flowing out of the petcock and onto the ground. Right?

Anyone want to try that?

 

[Cool Hand Lurker]

"What if you open the drain petcock for a few seconds while the engine is running (stationary in your drive) at high RPM? " Jim/TX

If you try the experiment and the radiator is plugged up, there will be a LOT of air being sucked in.
You know, this might be a good quick test to see if your radiator is plugged up. But you would have to know how much air would be sucked in with a perfect radiator for comparison. And the way you would make a comparison is by the sound difference between the two. Or maybe put a hose to a vacuum gauge on the petcock.

Hmmmmm..... another new idea!

 

[AlanD]

This is a post I made in another thread on this topic:

From this forum I read that the radiator by itself holds 1.5 gallons, and should empty in about 4 seconds. Before having my radiator roded out, it took about 9 to 10 seconds to empty.
I'm glad I made this measurement because I can really see the difference. After being roded out, it takes about 4 seconds to empty - as you can see in the video clip i made below.

It's interesting that it seems to hold nearly the same amount. I'm thinking that the capacity might not change much with plugged rods but the flow rate obviously does.
Alan

 

[Brentwood Bob]

Nice, Alan. This is the test my radiator man did on a questionable radiator to eliminate it. We went on to discover that the block was cracked. Bob

 

[pooch]

Recently I saw a tv segment on what would happen to your blood if you were depressurized to a near zero vacuum , ie, in space.

A beaker of room temp water was subjected to a high vacuum and it boiled.

Imagine your blood expanding by 1700 times inside your vessels.

ewwwww.