Water pump cavitation. Modifying impeller

29restorod

29restorod

Senior Member
Yesterday I made a 20 mile trip to test my cooling system in 92 degree heat. On the way to the afternoon cruise I kept the speed at 45 mph. The Moto meter stayed right at the summer indicater line. On the way home the temp was also staying steady,until I tried to bump the speed up to 50 mph. The temp shot up very quickly,and water started coming out the cap. I slowed down to 45 and the temp came back down. This would indicate to me the pump is cavitating at the higher RPM. I am using a Simmons high compression head,with a "B" cam,and a leakless water pump. I have read about grinding the impeller blades to cure this problem. How much should I grind off and what shape should I end up whith?
 
This is the slip of paper that comes in the Leakless pump from Brattons. It talks about how to grind the impellers if you are using a newer heavy duty radiator and their pump

waterpumpinstructions.jpg
 
A plugged radiator will cause that. Also, the new radiators have a similar number of tubes as original, but the tubes are much smaller in volume, so they will not flow as much water as a clean original. I solved that problem by installing a 160 thermostat. It slows down the flow enough to stop the problem, and the coolant stays in the system, and the engine stays cool. I was on a trip saturday with my 29 tudor, and the air temp was 91, and the engine stayed cool except on long steep hills, but it never boiled, or even got to the area of the circle in the motometer. I was traveling at 45-55 all the way.
 
Thanks for the replies. I did not get the instructions to the pump,because it was on the car when I bought it. After flushing the cooling system a few weeks ago things got better. I am trying to avoid buying a new rad,but if I go to the trouble of removing the old one,a new one goes in. I will save those instructions,in my log book,for this car.
 
Before buying a new radiator, you might try running some vinegar in it for a couple days. I've read good reports about it's cleaning effects.
 
It is my opinion that cleaning a Model A cooling system on the car requires a 2-step process. The first step is to remove the old grease that came in from the water pump. A detergent, perhaps?

The second step is to remove the accumulated rust. This is what the typical Auto-Store cleaners remove.
 
Auto store radiator cleaners sold today are too weak to remove any significant rust build up in your block. You need something stronger.

Look at Evaporust. It chemically reacts only with with rust, converting it to something else that goes into the solution.
 
A pump can not discharge more water than it can suck. Do you think there is a vacuum in the radiator? You probably a have a plugged radiator or a bad head gasket. You want the water or coolant to run as fast as it can through the whole system.

The pump will only cavitate if the the flow is stopped or the water temperate is close to boiling.
 
When rebuilding water pumps over the last 40 years and using the standard A water pump impeller, I drill a 3/16 " hole in each impeller to slow down the pumping action at higher speeds; it will also stop cavatation.

This is assuming you have a good radiator.

Ron
 
Ron in Quincy said:
When rebuilding water pumps over the last 40 years and using the standard A water pump impeller, I drill a 3/16 " hole in each impeller to slow down the pumping action at higher speeds; it will also stop cavatation.

This is assuming you have a good radiator.

Ron
Click to expand...
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.
 
It can't flow faster if there is a traffic jam. Try pouring a large bag of marbles into a funnel. Pour them as fast as you can and watch the funnel overflow.

Modern radiator cores have smaller tubes (like the small opening in the funnel) but more rows for more efficient cooling. So yes, you want to slow down the flow of the watter pump with a car with a modern core so you don't loose your marbles every time you drive it!! :)
 
Jason in TX said:
It can't flow faster if there is a traffic jam. Try pouring a large bag of marbles into a funnel. Pour them as fast as you can and watch the funnel overflow.

Modern radiator cores have smaller tubes (like the small opening in the funnel) but more rows for more efficient cooling. So yes, you want to slow down the flow of the watter pump with a car with a modern core so you don't loose your marbles every time you drive it!! :)
Click to expand...


It is a closed circuit. The pump can not pump more water than It can suck. Must be a plugged radiator or a cheap radiator that does not meet specifications.
 
Last edited:
The model A cooling system is part thermo feed. You can remove the water pump from the system by removing the belt; as long as you have a good radiator and the A is moving so air passes thru the radiator it will run at a normal tempature.
The water pump pulls water out of the engine into the top radiator tank, if the water does not move thru the radiator as fast as it is coming into the top tank, the excess will overflow into the overflow tube and this water is lost; this condition also cretes a void of water returning into the engine block which will cause cavatation and overheating. The water pump turns 1 1/4 times the engine RPM so slowing down the movement of water into the radiator I believe cn solve proplems. Just my opinion!!!!!!

Ron
 
Remove and try and clean your radiator first. I use lye (draino) and let it sit for about a 1/2 an hour with the bottom outlet plugged. Backflush the lye out and rinse good. wear googles. Sometimes it take 2 times or 2 bottles if it's plugged with stuff.
 
Sturgis is right.... on a closed system you cannot pump one drop more than you can suck. It is impossible to "pile up" the water in the top tank. However.... with increased restrictions, the pump will cavitate quicker. The other theory about the water pumping through the radiator so fast that it doesn't have time to cool is also pure bunk. Its not the way physics works. The surface area of the radiator and the temperature and volume of the air flowing over it is how the cooling is calculated.
 
"Sturgis is right.... on a closed system you cannot pump one drop more than you can suck. It is impossible to "pile up" the water in the top tank. However.... with increased restrictions, the pump will cavitate quicker. The other theory about the water pumping through the radiator so fast that it doesn't have time to cool is also pure bunk. Its not the way physics works. The surface area of the radiator and the temperature and volume of the air flowing over it is how the cooling is calculated. "

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.
 
29restorod said:
Yesterday I made a 20 mile trip to test my cooling system in 92 degree heat. On the way to the afternoon cruise I kept the speed at 45 mph. The Moto meter stayed right at the summer indicater line. On the way home the temp was also staying steady,until I tried to bump the speed up to 50 mph. The temp shot up very quickly,and water started coming out the cap. I slowed down to 45 and the temp came back down. This would indicate to me the pump is cavitating at the higher RPM. I am using a Simmons high compression head,with a "B" cam,and a leakless water pump. I have read about grinding the impeller blades to cure this problem. How much should I grind off and what shape should I end up whith?[/QUOTE

29restorod ...................
Water should not be coming out your cap, no matter what your problem is. It sounds like you need a better gasket in your cap.
MIKE :)
Click to expand...
 
You must log in or register to reply here.
Back
Top