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07-16-2012, 10:44 AM | #1 |
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Water pump cavitation. Modifying impeller
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?
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07-16-2012, 11:09 AM | #2 |
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Re: Water pump cavitation. Modifying impeller
My friend's did exactly the same thing and he had some plugged radiator tubes.
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07-16-2012, 11:59 AM | #3 |
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Re: Water pump cavitation. Modifying impeller
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
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07-16-2012, 12:13 PM | #4 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-16-2012, 12:58 PM | #5 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-16-2012, 01:24 PM | #6 |
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Re: Water pump cavitation. Modifying impeller
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07-16-2012, 03:20 PM | #7 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-16-2012, 03:41 PM | #8 |
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Re: Water pump cavitation. Modifying impeller
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. |
07-16-2012, 05:15 PM | #9 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-16-2012, 06:47 PM | #10 |
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Re: Water pump cavitation. Modifying impeller
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07-16-2012, 08:09 PM | #11 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-16-2012, 08:29 PM | #12 |
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Re: Water pump cavitation. Modifying impeller
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 |
07-16-2012, 08:44 PM | #13 | |
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Re: Water pump cavitation. Modifying impeller
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07-16-2012, 09:18 PM | #14 |
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Re: Water pump cavitation. Modifying impeller
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!!
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07-16-2012, 10:06 PM | #15 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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.
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07-16-2012, 11:24 PM | #16 |
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Re: Water pump cavitation. Modifying impeller
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 |
07-17-2012, 05:54 AM | #17 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-17-2012, 09:01 AM | #18 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-17-2012, 09:57 AM | #19 |
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Re: Water pump cavitation. Modifying impeller
"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. |
07-17-2012, 10:28 AM | #20 |
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Re: Water pump cavitation. Modifying impeller
[QUOTE=29restorod;462038]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 |
07-17-2012, 11:16 AM | #21 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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.
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07-17-2012, 11:30 AM | #22 |
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Re: Water pump cavitation. Modifying impeller
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. ...
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07-17-2012, 11:55 AM | #23 |
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Re: Water pump cavitation. Modifying impeller
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?
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07-17-2012, 12:07 PM | #24 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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.
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07-17-2012, 01:11 PM | #25 |
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Re: Water pump cavitation. Modifying impeller
My temp gauge probe is mounted in the Vintage Precision thermostat block, which puts it directly between the water pump and the upper hose.
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07-17-2012, 01:44 PM | #26 |
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Re: Water pump cavitation. Modifying impeller
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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. |
07-17-2012, 02:14 PM | #27 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-17-2012, 02:51 PM | #28 |
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Re: Water pump cavitation. Modifying impeller
Thanks Ron, I needed that! Makes me feel much better!
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07-17-2012, 05:38 PM | #29 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-18-2012, 04:50 AM | #30 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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.
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07-18-2012, 07:20 AM | #31 |
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Re: Water pump cavitation. Modifying impeller
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.
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07-18-2012, 08:51 AM | #32 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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 |
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07-19-2012, 02:50 AM | #33 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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?
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07-19-2012, 03:54 AM | #34 |
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Re: Water pump cavitation. Modifying impeller
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. |
07-19-2012, 07:24 AM | #35 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
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.
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07-19-2012, 07:32 AM | #36 | |
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Re: Water pump cavitation. Modifying impeller
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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?
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07-19-2012, 08:33 AM | #37 |
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Re: Water pump cavitation. Modifying impeller
"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! |
07-19-2012, 01:14 PM | #38 |
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Re: Water pump cavitation. Modifying impeller
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 |
07-19-2012, 01:52 PM | #39 |
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Re: Water pump cavitation. Modifying impeller
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
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07-19-2012, 06:06 PM | #40 |
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Re: Water pump cavitation. Modifying impeller
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. |
07-20-2012, 02:43 PM | #41 | |
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Re: Water pump cavitation. Modifying impeller
Quote:
This could be indicative of combustion gasses leaking into the cooling system.... head gasket or cracked head / block... My '28 has some deck cracks radiating from the exhaust valve seats on #2 and #3 cylinder towards the cylinder bores... it's okay loafing around town, but if I pull a steep hill and have my foot in it, she'll blow steam / water out the overflow... |
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07-20-2012, 07:00 PM | #42 | |
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Re: Water pump cavitation. Modifying impeller
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