Legends and old wives tales

SuperDave

Every now and then the subject of thermoststs and overheating comes up. here on this forum and other car forums. The notion that slowing down the flow through the radiator so the heat can be disapated is erroneous. I know this is going to rub some folks wrong. Ever since the first guy tried to race a flat head Ford V8, they thought that puting a restrictor in each water outlet slowed down the water, so it could be cooled by the radiator.Those engines had two water pumps, one for each bank of cylinders and two outlet pipes to the top tank.YES placing a restriction or thermostat on the outlet of the water pump usually cures the problem of overheating.. But it is not a cause an effect that one might think. A man by the name of Stewart (sp?) Makes water pumps for the Busch & Nextel Cup cars. He built the worlds first water pump dino. He proved that you can't circulate the water too fast. What happens is the pump vanes cavitate when the pump is turning at high speed. That coupled with gas bubbles circulating from hot valve pocket areas gathers around the impeller and the pump STOPS pumping. By placing a restriction on the output of the pump, a high pressure area is created at the impeller that prevents the cavitation. hence, the pump keeps circulating water. This can be demonstrated by trying to place the restriction at the INLET of the pump or at the bottom of the radiator. If just slowing down the water was keeping the engine cool. this should work. But it doesn't. In fact the engine will overheat much quicker than if it had no restriction at all. I have seen this demonstrated on stock cars. Also grinding down the impeller to slow down the flow of water seems to help, but actually since the impeller isn't cavitating as much, the cooling is helped. I am not an engineer, just a frustrated shade tree mechanic and always believed the theory, but he made a believer out of me. I had this discussion with a fellow short track racer.He said i was full of it... he put a 5/8 restrictor hole in a piece of pipe and placed it in the lower hose of his 358 Chevy motor (with a 14# cap). The same piece he had been running in the outlet hose on top of the engine. It took 3 laps to reach 250 degrees and boil over. He put it back in the top hose and ran the entire 20 lap feature race at 210 degrees and no overheating.If you think about it, why do all the factorys put the thermostat on the outlet side of the pump? I'm sure they learned many years ago that was the only place they worked properly. Now this should start a lively discussion... Fire away..

Dave w. :eek:

Uncle Josh

As a mechanical engineer with some hydraulic pump experience, it makes perfect sense to me, and I'm glad to get the education. Thanks.

[Deleted User]

As a devout neophyte in the world of mechanics, I can say without hesitatation, that I did that to my 66 VW bug and didn't notice any difference. LOL...

[Deleted User]

Damn, my old Corvair had a similar result!

Unknown

Thanks also, Dave, for the education. I always thought that the main purposes of the thermostat was to: a) keep the engine at a more constant operating temperature (obviously), and b) let the coolant heat up faster so that the heater works sooner. Now I understand that the latter is merely a beneficial side effect of a thermostat. Creating a back pressure on the outlet side so that the water pump impeller doesn't cavitate seems to make more sense. This would also explain why thermostats come in different degree settings, since I would assume various engine designs would have to have coolant restrictions released at different temperatures depending on their design and optimum operating temperatures.

Unknown

Did you ever think that this fellows mission is to sell water pumps and convince people that he was the water pump guru.

SuperDave

Martin200 wrote:

Thanks also, Dave, for the education. I always thought that the main purposes of the thermostat was to: a) keep the engine at a more constant operating temperature (obviously), and b) let the coolant heat up faster so that the heater works sooner. Now I understand that the latter is merely a beneficial side effect of a thermostat. Creating a back pressure on the outlet side so that the water pump impeller doesn't cavitate seems to make more sense. This would also explain why thermostats come in different degree settings, since I would assume various engine designs would have to have coolant restrictions released at different temperatures depending on their design and optimum operating temperatures.

I am sure you are absolutely right. The primary purpose is to control temperature and an engine operating at a proper temperature is more efficient. The prevention of cavitation is just a side effect. According to other more educated power plant gurus, we are circulating the coolant in the wrong direction. A whole 'nuther subject! Seems like we never quit learning.

SuperDave

tombpa wrote:

Did you ever think that this fellows mission is to sell water pumps and convince people that he was the water pump guru.

Sure Tom. I am skeptical of most stuff I hear that is foreign to me. It Comes with getting older and wiser. I am very familiar with the old saying. "If you can't dazzle them with brilliance, baffle them with B--- S---!" The article I was referencing was a very detailed (backed up with solid engineering data). Yes He IS a water pump Guru. Not by his definition, but by those that have used his ideas and products. He has solid credentials. He has designed and manufactures very high quality parts. It's also interesting to note, that his article gave information to help other racers correct a problem WITHOUT having to buy his product. Most racers don't need the expensive Stewert pump. His paper was published in Stock Car Racing or Circle Track magazine ( don't recall which)and was a reprint of a paper that was published in Society of Automotive engineering official publications. So far, no one that has any experience in the field has questioned his results. No doubt someone has tried to prove him wrong..but so far, his data stands. There was additional engineering data accompanying the article that I could not comprehend due to my lack of education. It delt with thermodynamics and how heat is transfered. His statement that coolant can't be circulated too fast was backed up by other thermodynamics engineering data that HE didn't generate. He just quoted the formulas and test results from those experts. Again, no negative feedback from engineers in that field. No doubt that a radiator that doesn't transfere heat will cause overheating but slowing the flow down would make the problem worse. Here in the salt atmosphere of the Florida coast, many radiators fail due to fins not making good contact with the tubes and not dissapating the heat. Our Hudson radiators were of a superior design and don't seem to fail for those reasons.

All this considered... The Hudson step down engine is a slow turning engine by todays standards. Cavitation of a water pump should never happen under normal circumstances. There usually is some other undetected defect in the system that causes overheating. Leaking head gasket, improper timing, clogged radiator tubes, defective thermostats..All of which have been coverd here in this forum from time to time. (I think the pre step down with no pressure cap could benifit from being pressureized is being used in a severe application.A/C?)

The cooling system of the Step Down engine was way over engineered. I have the original untouched radiator in my 49 262. It's never been recored or rodded out. I also have airconditioning with the absolute stock fan. Here in Hot Florida the temperature never goes over 205 degrees at idle at a traffic light. I am measureing the coolant at the outlet of the thermostat housing with a direct reading capilary tube guage. 180 degree themostat. The moment the car starts to move forward forcing additional air through the radiator, it cools to 180-190. Do we have great cars or what?

Also for those that read all the numbers. I mis stated the pressure cap pressure on the circle track car i mentioned. the correct cap was 22#.

bob ward

Thanks Dave, I've always been septical of "the engine's overheating because the water is going through the radiator too fast" but was always at a loss to explain the apparent benefit of restricting the water flow. But it does seem plausible that restriction improves the performance of the pump.



The cooling capacity of a radiator is based on:-

•Surface area of the radiator

•Temperature difference between the radiator and the ambient temperature

•Airflow through the radiator



If the water is 'too fast' it just means the water goes back through the radiator more frequently. Lots of small quick cools rather than fewer long cools.

Geoff

Hey, I've been driving my 1928 Essex for fifty years, and NEVER had water pump cavitation. Nor have I repacked it, never replaced the thermostat, and never had overheating problems.

Geoff.

[Deleted User]

The problem range for cavitation is usually the rpm band from 4500-8500 rpm. Below 4500 you will rarely find these problems unless you are building up pressure due to blockages caused by rust issues or something like that.

J Spencer

I was always led to believe the theory of going through the radiator to fast could lead to overheating. This man may be correct, but to correct the statement "that is why all the manufacturers put the stat on the outlet side" not true some imports have done this -- Mercury Capri V-6 in the 70's and the GM 2.3, 2.4 OHC four bangers is on the inlet side. and correct me if I am wrong but the Chevy V8 in the mid 90's had reverse cooling flow which would then put the thermostat on the inlet side.



JSpencer

[Deleted User]

J Spencer wrote:

I was always led to believe the theory of going through the radiator to fast could lead to overheating. This man may be correct, but to correct the statement "that is why all the manufacturers put the stat on the outlet side" not true some imports have done this -- Mercury Capri V-6 in the 70's and the GM 2.3, 2.4 OHC four bangers is on the inlet side. and correct me if I am wrong but the Chevy V8 in the mid 90's had reverse cooling flow which would then put the thermostat on the inlet side.

JSpencer

My 95 Corvette LT1 (which is going in my '50 Pace) has the reverse flow cooling system. It is also said to allow higher HP and better fuel economy (stock 300hp and 24-26mpg-w/ 3.08 gears) with today's smog requirements. But, I am no expert in this area. Am told I will have to use a radiator specific to the reverse flow system, but haven't got to that point in the build yet.

Very interesting info guys.

Jay