Thermostat data, not opinions

[krswen]

you're absolutley right ..... I fell into the same trap of loose technical language that I criticize my students for! There is no such force as suction. The flow is driven by atmospheric pressure in the headspace of the upper tank seeking to fill the void created by the water pump impeller blades expelling water radially out from the channels. This differential drives the flow. My concern is that since the upper bound of the pressure differential (we call it "delta P") cannot be higher than what it takes to lift the flow to the upper tank (about a foot I think), the lower limit will be sub-atmospheric and that can lead to cavitation. But from what I have read in past postings, apparently that is not an issue in the Model A system.

[Frank Miller]

Even though there is no pressure pumping water into the top tank increases the pressure at the bottom of the inlet. The interesting thing is that as this discussion goes on we are becoming aware of all the dynamics going on in the cooling system. Regardless of whether the pump sucks or blows the important thing is it is doing its job. I personally think a thermostat will help the engine reach its operating temperature quicker and also maintain it in colder weather. This is important to drive any water vapor out of the oil.

[Leslie Pam]

I run an extreme heavy duty radiator that the local shop built and on my fully pressurized engine with a sealed bearing waterpump and a 6 bladed plastic fan, the engine never got over 110 degrees even on the hottest days as measured from temp guage installed in the water neck on the head. Too cool for best engine performance. I added a 160 degree thermostat and drilled out the 1/8th hole to 3/16th and added an additional hole for more flow while the thermostat was in the closed position. The engine runs about 160-170 under most conditions and even with the large 1930 california plate in the original position while climbing hills in Yosemite where the temp was over 100 degrees, the engine never went over 195 even on the longest climbs. I have only had to add 1/2 cup water at the most during the worst conditions.

[Special Coupe Frank]

Originally Posted by 40 Deluxe

Just throwing out something to mull over while lying awake at night: several posts refer to the "suction of the water pump", but technically there is no such thing as "suction"! Picture drinking a glass of water through a straw. You expand your lungs creating a low pressure area in your mouth and throat. Atmospheric air pressure (14.7 lbs./sq. in. is pushing down on the surface of the water in the galss) always moves from an area of higher pressure to an area of lower pressure. Thus atmospheric pressure pushes the water up the straw into your mouth as it seeks the low pressure area of your lungs. You are not really sucking water up the straw! In the Model A, as the pump pushes water up into the radiator, there is less water now at the pump inlet so there is a low pressure area there, so atmospheric pressure in the upper radiator tank pushes more water into the pump impeller as it tries to reach that low pressure area. The pump doesn't really "suck" anything. A vacuum cleaner doesn't suck up any dirt, either! It creates a low pressure area inside the tank or bag and hose so atmospheric pressure again tries to equalize the pressure inside the vacuum cleaner so it pushes its way into the hose, carrying dirt with it (introduce a low pressure area above the dirt, and the atmospheric pressure under the dirt pushes it into the vacuum). One more point: Can you pull (or suck) water through a hose? How? Do you put a hook in the water to pull it, or tie a rope to it? No! A liquid (like air) can't be pulled, it has to be pushed.

Yes, this is correct from a scientific standpoint.

But folks have been talking about "suction", "vacuum", etc for several centuries... clinically correct or not, it seems to get the point across.

[hardtimes]

Originally Posted by marc hildebrant

Group,

Recently I cleaned out my radiator with "simple green". I also replaced the 50/50 antifreeze coolant with water. Good reason for a road trip.

Air temps in the mid 80's today. Started out at 5000 ft. The engine temp ran up to 160 as I approached the Foothills of the rocky mountains.

Drove up to Jamestown CO at 7000 ft. Great ride up through a nice canyon. Car temp stayed around 160 the whole way up.

Drove back down...through the canyon the temp went to 100 as I dropped 2000 ft.

Back home in the city, around 150.

I do not have a thermostat in the car....but....seems that I could use one to keep the car from cooling down !!

Marc

Marc,
Thanks for the stats! Your stats prove, again, WHY the use of a t stat is good for an internal combustion engine:i.e.-quick engine warm up and maintenance of maximised engine temp equals= effiency, longevity,best gas mileage , cleanliness internally , discourage acid/waste build..on/on! Hmm, wonder if any modern engine engineer would recommend running an engine without a thermstat? If you really don't think and/or care about any of these benefits, that's 'cool' too. Just get in and drive it and have fun ..till you wear it out!!

[Larry Brumfield]

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Originally Posted by Special Coupe Frank

Yes, this is correct from a scientific standpoint.

But folks have been talking about "suction", "vacuum", etc for several centuries... clinically correct or not, it seems to get the point across.

You're exactly correct!

People have an immediate connotation or thought in their minds when they hear the words suction or vacuum.

"Mr. Grocery Boy is this food vacuum-packed?"

"Well no, the atmosphere is pushing down on it"

"What?? Well I don't know if I want it now, smart aleck. Let me speak to the manager!"

Of course if the lid were opened the air would rush in.

I remember watching a demonstration put on by an engineering prof. one time with an empty steel drum. The prof had a VACUUM pump hooked to it and when it SUCKED a VACUUM the steel drum caved in like a crushed beer can.

The prof. asked, "Did the VACUUM SUCK the drum in or did the weight of the atmosphere push it in?"

One student yelled out, "You suck!"

The prof. didn't quite hear correctly and said, "Wrong! .... the weight of the atmosphere pushed it in."

The students roared with laughter. The prof. looked puzzled.

Now switching gears a little .....

The Model T cooling system works on the principle of thermo-syphon with NO water pump. The water gets hot and rises, moves forward up the head's water hump and the thermo-syphon action begins.

The Model A works the same way except it is assisted by the pump to move the water. My contention is that the weight of the atmosphere in the headspace of the upper tank plays a minimal role and hot water is constantly rising up and moving forward behind the water pump in the head with a fresh supply to be caught by the impeller blades and then moved up the hose plus naturally rising and moving that direction from being hot. Once in the radiator the water cools, gravity assists and the weight of the water volume pushes down in addition to a natural draw or suction at the block entrance.

I'll bet that if the water stayed cold and the pump turned, the pump would soon cavitate or the flow would be very poor at best.


Larry B.

[cars56]

Wow, these post are great! Copying the thread to add to my A tech binder.
Running Purple Ice 2 to keep temps low, maybe not such a good idea if not in the 160 range. Installing a temp guage to monitor engine, particularly on warm up.

[Gord. B by the bay]

Marc yes it did have a thermostat Gord. B

[Purdy Swoft]

Originally Posted by Kirby1374

While reading this all I could think of is what Frank Miller said

Yeah! Frank is RIGHT.

[hardtimes]

Originally Posted by krswen

I’ve been pondering the advisability of using a thermostat. Here’s why.

The Model A cooling system is very primitive compared to more modern cars. Today, when we design an engine, the water pump is situated so that it pushes coolant into the engine, usually the block first, then through the cylinder head(s) and finally to the radiator. The impeller is designed with very specific blade shapes so that the “incidence angle” of the incoming flow is minimized. The engine represents a resistance to flow which plots as an upward turning parabolic when plotted on a pressure vs flow “performance map” of the pump. We match the resistance curve with the pump size to center the curve in the “sweet spot” of pump efficiency.

In the case of the Model A, the pump is at the engine output side of the flow circuit and all the pump does is to raise water to the height of the upper radiator header tank. Density changes, which result from the heat exchange process in the tubes and fins, cause to water to sink down to the bottom of the radiator. The pump DOES NOT push water through the radiator. It cannot since there is “head-space” in the upper header tank and it is not pressurized.

On modern engines with a thermostat, it is plumbed so that when the thermostat is closed there is an “escape route” back to the engine inlet so the flow is never stagnated and the pump is never “deadheaded”.

In an A with a hot water heater (rarely done as far as I can tell) the heater circuit would provide similar relief.

However in a typical A with a thermostat in the upper hose, when it is closed the pump will be deadheaded and the impeller will be churning in non-flowing water. For modern water pumps this would be a VERY bad thing, leading to possible cavitation and impeller erosion. The A impeller has only three blades and seems to run with rather generous (by today’s standards) clearances. Maybe it doesn’t care.

There seems to be a lot of discussion in the threads I’ve found about the desirability of “slowing the flow down” in the cooling circuit. Let’s think about that for a minute. In a compact heat exchanger (the term we use in engineering to describe automotive radiators) one of the performance parameters is the flow velocity through the water tubes. The heat exchange generally improves with higher, not lower, velocities. Balanced against this however is what we call “residence time”. The longer the coolant is in the radiator the more heat it can reject to the air (in a cross-flow design which is what radiators are). However, that same increased residence time means that coolant in the engine has more time to gain heat … maybe enough to reach boiling. Also slower flow through the engine means that the temperature difference from inlet to outlet is larger, possibly leading to increased thermal stress and distortion.

So here is my question: has anyone done controlled experiments to determine if adding a thermostat has any beneficial, or deleterious effects on steady-state cooling? No argument that during warm-up (what we call “transient conditions” in engineering) you can get the engine up to temperature faster. But is it worth the possible downside effects of impeller wear and the greater thermal gradients that have to occur in the engine with longer residence time and slower flow?

Thoughts or experiences from those who have done experiments with PROPERLY running cooling systems before the thermostat was installed?

"THOUGHTS"...Have you thought about the following, as a possible experiment to show whether the model A "water moving device(pump)" SUCKS OR PUMPS OR DOES ANYTHING TO CIRCULATION: some say that the model a water system cools due to thermo circulation(hot water rising) like a 'model T' , only with addition of suck/pump device added. Also, saying that the 'sucker/pump' is not responsible for MAIN reason of water recirculation/flow. I propose running the suck/pump WITHOUT the water system being heated...and we shall see whether the suck/pump cavitates/ pumps/circulates!! WHAT will happen?? The sucker/pump could be operated via an electric motor and belt. With no heat to 'thermocirculate' the system...what do you think the suck/pump will show?? Ok...one NOS quail to the person with the right answer(grin)..you pay shipping! lol

[Special Coupe Frank]

For what it's worth, when I did my little petcock experiment described in post #13 ( engine running at fast idle ), the engine / cooling system were dead cold, so I don't think thermo-syphon was entering into the picture in this particular instance.

[Larry Brumfield]

Originally Posted by Special Coupe Frank

For what it's worth, when I did my little petcock experiment described in post #13 ( engine running at fast idle ), the engine / cooling system were dead cold, so I don't think thermo-syphon was entering into the picture in this particular instance.

Try the experiment again except this time make sure the water level is well below the overflow tube opening.


Larry B.

[PDXCougfan]

Y'all are gonna make me break out my transport book and model it arent you? LOL...The model is actually not that hard to setup...you can use a 2-D heat transfer model/mass balance using cylindrical coordinates...If I had access to Fluient i would model it up really quick in 3-d...but i dont.

Cooling rates and thus steady state temperatures, are going to be driven by (assuming :
1) air flow speeds over the radiator surface.
2) the radiator surface area (including fins)
3) Water pump rate (mass flow rate) (dont care if you call it suction or pressure...flow is driving by a pressure differential from the pump and to a lessor degree the thermal diffusion and density gradiants...)
4) AIr temperature (needed for the driving force for thermal conductivity)
5) Water temperature
6) Water thermal conductivity with antifreeze.

[Larry Brumfield]

Here's what Ford's original Model A Instruction Book says that came with the car. You know .... it's the one that none of you read.

Page 19

The Ford Cooling System

Cooling the Engine

The Ford engine is cooled by a circulation of water through the water jackets which surround the cylinders, combustion chamber and valve seats. The water is CIRCULATED by THERMO-SYPHON action, the flow of water being accelerated by means of a centrifugal water pump located in the front of the cylinder head. This pump DRAWS the heated water from the engine into the upper radiator tank where it is cooled by filtering through the radiator tubes to the lower tank.


Larry B.

[krswen]

Hi PDXCougfan ...

I'm thinking of modeling it with GT Cool (part of GT ISE suite of programs), but first I want to get my GT Power engine model up & running. I'm sure I'll be pestering the folks on this site for info like cam lift tables etc.

I think we have Fluent, but I've never used it.

Ken

[marc hildebrant]

"Here's what Ford's original Model A Instruction Book says that came with the car. You know .... it's the one that none of you read."

Read mine before I drove it anywhere.

Marc