My 1930 Plymouth has a thermosiphon cooling system like a Model T but it includes a small bypass hose that runs between the inlet and outlet hoses. What purpose does it serve and would a Model T benefit from a similar bypass? I doubt they would have provided for it if it didn't have some beneficial function.
I would not change the Plymouth to be like the Model T nor vice - Verza. Different engines, different engineering. The Model T cooling system works perfectly as designed. Don't screw it up!
Does it have a thermostat? Is 1930 Plymouth a 4 or 6 cylinder?
Royce I am not looking to change anything but wonder why there is a difference in how the two manufacturers approached the same technology. They are both 4 cylinder cars and neither of them were built to use a thermostat. Ford was still using a cooling system from the birth of the Model T right up until the end of production. Chrysler was in the process of developing a more modern car and presumably improving on past technology. I am assuming there was a reason why they did it and was wondering if anyone knew what that reason was. Depending on the answer it might or might not be an improvement. In any event I still would like to know if anyone can explain what purpose the bypass was designed to serve.
I don't know anything about Plymouths, but from an engineering perspective, I would speculate, and it is only speculation, that they were attempting to "pre-cool" the inlet to the radiator. The bypass hose you are describing in a thermo-siphon system could only produce flow in the direction of "from-cool-to-hot", and the only reason I can think of that they would want this would be to dilute the hot radiator inlet with some cooler water. But Royce is correct, just because Plymouth needed it for their 1930 design does not mean that a Model T needs it. The engines created a different amount of heat and their radiators were of different capacities, so what was required on one was not necessarily required on the other.
I think we all know that a bypass is not required on a Model T any more than, if you will pardon the expression, a water pump! I am not sure that it is required for effective cooling on the Plymouth either as I have never run the car without it. If I understand what you are saying Richard some of the cooled water is redirected back to the radiator without passing through the block in order to further reduce the temperature of the coolant in the radiator and I expect that by doing that the temperature of the coolant actually entering the block is lower so the cooling effect is enhanced. That may explain why the temperature of the coolant in the top tank of the radiator on my Plymouth is a constant 160 degrees once it warms up regardless of how hot it is outside. I think I got my answer! Thanks.
If it has a thermostat, it is probably a bypass line to allow the engine to come up to temp more quickly. Many farm/industrial engines had them, but typically with a water pump. I have a Hercules JXD in a shovel that has a 3/4" bypass line that is open when the thermostat is closed. As the thermostat opens, it closes off the bypass line and directs flow through the radiator.
Nick that is interesting. To my knowledge the car never had a thermostat but what you are saying makes sense. The metal tubes between the hose sections have the outlet for the bypass integral with the tubes so I am assuming it is original to the car as I doubt that anyone would go to the trouble of adding something like that later.
Did the car ever have a heater? Some one may have bypassed it.
No it never had a heater and I was under the impression that you cannot have a heater that uses the heated water from the cooling system without a water pump. When I bought the car in 1962 from the elderly original owner he said he was selling it because his wife was ill and they needed a car with a heater. He actually bought a new Plymouth Valiant to replace his 30-U.
I tried but I was not able to find a photo of the left side of a Plymouth 1930 4 cylinder thermosiphon engine. If you have a chance, please post a couple of photos showing how it is set up and photos that show the by-pass you are discussing. I did find one photo of a 1932ish 4 cylinder that had a water pump at the front. It appeared to also have a block off plate on what I would “guess” was the previous water inlet that had been used when thermosiphon was the method of cooling? See the photo below from: http://www.allpar.com/photos/plymouth/1932/flathead-four.jpg
If your by-pass is uphill from cold to hot, I suspect it would do very little transfer. I.e. the hot water rises and the cold water sinks. If there was a good flow of water it is possible for the venturi effect to draw some of the colder water up hill – but I suspect but I do not know – that any venturi effect would be minimal at those fluid speeds.
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Hap that set up looks like it was modified to supply a heater core. I just can't figure out from your picture how the coolant gets back into the radiator. I will try to get some pictures today of my set up but the car is partially apart right now for restoration. On my car, which does not have a water pump, there is a bypass hose running from the upper radiator hose in your picture to the lower radiator hose. The lower radiator hose runs from the blocked off inlet to the lower radiator outlet. There is a metal pipe inserted in each of the hoses similar to the lower hose set up on a Model T and each of those pipes has an integral pipe for the bypass hose. Unfortunately, one of those pipes has deteriorated and I am trying to decide if it is worth making up a replacement or just eliminating it. Based on what you are saying It sounds like it is not worth having but I still can't get over the idea that they would not have gone to the trouble if it didn't do something positive.
Here is a picture of the bypass set up. I have the original metal sections where the by pass is mounted but they were replaced with a one piece hose after they started to leak
I looked up Plymouth thermosiphon the other night, and I believe 1930 was the last year, and that it was changed over to waterpump mid year (with only one model still being thermosiphon at the time).
I suspect the engineers had good reason for it, and after 15 million Ts, it's not hard to suspect some improvements were thought of. Maybe, as with the Model T, restoring to original is a good way to go. If the bypass is detrimental, or useless, it could easily be plugged while keeping the original appearance?
Rob you are right about the switch to water pumps in 1930. My car is a very early 30-U and is more like the 29-U than the later 30-U engine. I guess I will make up new pieces for the bypass. I just wish I could get some input on what the purpose was. The only thing I can think of is that it might help warm up the car faster because some of the hot water would drop down and recirculate through the block before it was cooled by the radiator. Once the car was warmed up the thermosiphon effect would increase the flow and reduce the amount of coolant, if any, that ran through the bypass. In a sense it would be acting like a thermostat. That is just a guess on my part and I was hoping someone would either confirm that or supply another explanation.
You might replace the hose with clear plastic tubing and (maybe)see what kind of fluid flow you have. It could be that the bypass was some engineers wonderful but unnecessary idea.
Water will go uphill from cold-to-hot, otherwise it would never go from the radiator outlet to the engine block in a normal thermosiphon system. The driving force is the hot water rising which "draws" the cooler water up. The hot water cannot rise unless the cooler water below follows along to fill the void. So it still seems to me that the design was an attempt to pre-cool the radiator inlet. But I also agree with Ted that it may have been an attempt that didn't really work very well. There may be little or no flow actually going through that line. Sounds like they changed to the water pump soon thereafter, so that may be the proof right there that it was not giving all the benefit they had hoped for.
I'm trying to think this through. You mentioned maybe some water passes down, until the thermosiphon effect takes over (I'm paraphrasing, so feel free to tell me I'm all wet, pun intended). However, no water should move down, water will only move up (unless you were somehow introducing cooler water from the top of the radiator/engine) either through the bypass, or main system, due to heating water.
It seems to me, the bypass will allow water to move through first, when very little water has warmed (or the heat from the engine is minimal, such as when starting a cold engine). When the thermosiphon is fully engaged, in other words the engine is hot, I can see the "hot" engine water overiding or stopping the cooler bypass water in it's tracks. Again, I think pure physics will dictate if water moves upward through the bypass or main engine system.
So, if the engine is running warm, dissipating heat to the water in the head, this water will obviously be warmer than any cooler water that moves upward from the radiator bottom to the bypass,and effectively shut the bypass water off. If this is true, then the bypass can't hurt cooling when you need it.
Hmmmm. Sounds reasonable. But I've had a few beers.......
I would recommend finding some photos or illustrations from 1929-1930 showing that engine. I suspect that bypass hose will not be shown. Or if it is shown, hopefully they would have an explanation of what it was there for. Does anyone have some references for a 1930 four cylinder Plymouth?
Note we only need someone with access a fluid dynamics laboratory and they could quickly tell us if any coolant flowed through the by-pass hose or not (and we would need the engine to be heated if it did not run). Or someone who can put the data into one of the flow calculators on the internet.
I've never taken fluid dynamics. But they talked about it briefly in a couple of classes I took. From what I can see in your photo, the upper and lower radiator hoses are the same size. Therefore the fluid flowing through both of them should be going at the same rate and the same volume of fluid. I.e. as the warm water rises from the engine outlet towards the radiator and equal amount at the same flow rate would exit the radiator at the bottom and move towards the inlet side of the engine. If that is correct, then there would not be a venturi effect at the upper outlet. The pressure would be the same in all locations. If there was a section of the upper hose that necked down to a smaller diameter and the flow was fast enough, it could cause a venturi effect and suck water up through the bypass. But again I suspect with the thermosyphon flow it would not be enough to make any difference.
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being from the northern part of southern Missouri and half hillbilly and redneck and if the half stopped up radiator and no money for a new radiator. I might think a venture tube in the top hose would pull cool water up to mix with the hot water so the radiator would not have to work as hard. If it worked it worked and if it didn't it did't, and not out much money.
I took fluid dynamics 25 years ago, which is as good as never with my memory, LOL! This topic got me interested so I went and looked and I still had my textbook, but it was no help for a thermosiphon system. A system with a non-constant density tends to make the equations too complicated for university students I guess, so they didn't really talk about it. I think it's a marriage between fluid dynamics and thermodynamics which is pretty hard to model but I'm sure computers can do it.
But I think the key here is the simple U-tube effect (not made up, this is an actual thing we use in the oilfield). Imagine a U-shaped tube. In the left hand leg of the U there is a heavy fluid. In the right hand side of the tube is a light fluid. What will happen? The flow will go from the left hand side to the right hand side. Pressure wise, this is because the hydrostatic pressure at the base of the left hand (heavy) side is higher than that at the bottom of the right hand (light) side. So that is the pressure difference driving the flow from the left side to the right side.
So translate this to the car. The column of water in the radiator is the left hand side (heavy) of the U-tube. The column of water from the top of the engine block to the radiator inlet is the right hand side (light) of the U-tube. So the water flows down and out of the radiator and up and in to the engine block.
So thinking about this principle, will it work with the bypass tube? I think probably not. Because the temperature, and therefore density, of the water in the bypass tube is the same as what is in the radiator, there is no density difference, no hydrostatic pressure difference, no flow into the tube. In fact, the water in the bypass tube is probably cooler (heavier) than what is in the radiator, because the radiator water is still warm in the top half (at normal engine operating temp). So, if anything, the flow in the bypass tube would be down the tube and back into the engine block (so my stance has changed from previous posts) but only when the car is at operating temperature, not at start-up. And the flow would not last long because as it was replaced with hot water, matching the density of the water in the engine block, the densities would equalize and the flow would stop.
(At start-up, the temp in the bypass tube and the radiator and engine block is exactly the same so no flow anywhere- the thermosiphon system self-thermostats itself. The water in the engine block is static at start up until it heats up enough to create the hydrostatic pressure decrease to allow cool water to start dumping out of the radiator).
The Venturi effect won't come into play because the flow in a thermosiphon system is just not high enough to create the velocities required. They work with high flow air in a carburetor with purpose-fit jets, but not so well in slow moving fluids in radiators, hoses, and water jackets with no jets.
Sorry for the long post. I go nerdy on theoretical discussions, and writing this stuff out helps me understand these old cars better.
Perhaps an old shop manual from the era would have something to say about it. To me, it seems to have no use at all.
I agree with Richard about not enough flow to make the venture work in a thermosiphon system, but the plymouth had the sinful water pump, now my question is with the water pump would that give enough flow
I am afraid that what I thought was going to be a fairly simple question has turned out to be a lot more complicated than I expected. I appreciate all the input and suspect that the bypass may not be necessary but since I ran the car with it for more than 10 years without any cooling issues I think I will continue to use it when I am finished with the restoration on the theory that it may not help but it clearly does not hurt! I am going to try and get some information from period material on the issue and If I find out anything interesting I will post it. Thanks to everyone for the input.
I cannot think of any reason that cold water would flow UP that bypass hose. Cold does not normally rise, and the source of heat is the engine. Hot water would flow out of the head into the radiator and be replaced by cooler water from the radiator. There is no reason why hot water in the upper hose would flow DOWN that bypass hose. Unless I'm missing something, that looks like some shade-tree mechanic's brilliant idea to accomplish some function that defies thermodynamic law.
Looking at the picture, that "bypass tube" was probably not original equipment. It is someone's band aid.
I bet there was a hot water heater in the car at some point, and the heater core leaked, leading some one to install the heater hose as you see it to stop the water leaking into the interior of the car.
Here's a 1930 Plymouth engine not equipped for a hot water heater -
Royce, when I bough my car in 1962 from the elderly original owner he was selling it because his wife was ill and they needed a car with a heater. My car never had a heater and I believe it is impossible to install one in a car with thermosiphon cooling without adding a water pump. it may be that the car in the picture you found does not have the bypass because the metal tubes that connect the hoses and have the pipes for the bypass had rotted away and were discarded. One of mine rusted away and the other one is in very poor condition. What your picture does suggest however is that the bypass is unnecessary and can be eliminated which is good news as it means I don't have to replace the metal section and can eliminate 4 hose clamps.
Lots of cars with thermosyphon - many, many Model T's - had hot water heaters. I used to have one in my '17. It connected exactly as the connections on your engine are oriented, and it worked well. It clamped to the steering column, and the hoses went through the floor boards. The same heater would have worked fine with your car.
Water moves through the heater as it does through the radiator - hot water rises, and cool water returns to the engine inlet. A hot water heater is in effect an additional radiator.
Rock Auto has the 1930 Plymouth owners manual for $17.10
Thanks for the info on the owners manual Ted but I have the original one from the first owner and it does not show the radiator hoses. The pictures just show the inlet and outlet pieces on the block and head respectively.
I apologise for taking up so much time for a competitors product but at least I now know that you can put a hot water heater in a Model T and that's more than I knew yesterday!