I am happy to accept that what you say is true. But I would like to understand the underlying theory. I have only limited experience with old Holdens and old Fords. >From memory the flow of coolant left the bottom of the radiator after it had been cooled and made its way to the pump. After the pump it made its way to the block. And lastly thru the thermostat to the top of the radiator= .. I think (I am most likley wrong) it had only one path from the pump to the block so it was unable to circulate coolant other than thru the block and back into the radiator. As you say there have been many makes and models of engines and perhaps they allow coolant to circulate freely while the thermostat is in its closed state but from memory this is not what I have seen. In any case I am unable to understand how it would overheat if the return flow to the radiator was less impeded and would welcome a more detailed explanation. I did like the explanation with regards to air pockets forming in the Miata that was previously discussed but I finding it hard to apply this generally= .. My motor mech teacher taught that the coolant didnt have time to collect the heat from the block if the flow was too fast and I always had difficulty accepting this. But I have since pondered why he said this and thought there must be hidden truth. So in conclusion, if the coolant can circulate thru the block while in the closed state or if air/steam pockets form while in the removed state then I must accept that engines may overheat if the thermostat is removed. But I dont think this applies generally. Please correct inform me either way. Curiously Justin PS closed state refers to closed with a bypass hole. On 24/11/2014 6:11 PM, "Richard R. Pope" wrote: > Hello all, > I am going to answer several different replies at the same time. > First of all to make the blanket statement that and I > quote, "A motor vehicle engine does NOT > run hot if you remove the thermostat." is incorrect as soon as it is > said. Yes, most of the iron duke engines that were being produced by > American manufacturers would not overheat if you ran them with out a > thermostat. The radiators were usually over-sized and the bypass holes > were small. So only 10-20% of the coolant flow would be bypassing the > radiator as the engine ran. If it was cool outside they wouldn't even > get up to operating temperature. This would cause poor engine > performance, excess fuel consumption, oil dilution, and poor heater > performance. > Most European and some Japanese automobiles have engines that will > overheat if they are operated in moderate to high temperatures with out > a thermostat. The bypass hole can be large enough that up to 50% of the > coolant is flowing right back into the engine and it doesn't go through > the radiator. Also the radiators are engineered to be just large enough > to keep the engines cool in the highest possible temperature were the > car is expected to be operated. If the car is expected to always be > operated in the far northern or far southern latitudes it will possibly > have a smaller radiator than the same car that is expected to always be > operated in latitudes that are closer to the equator. > Will an engine overheat with out a thermostat. It depends. The > thing about cars is that if you can save a pound on the cooling system, > and a pound on the electrical, and a pound on the body, and a pound on > the interior, then you can remove a pound on the frame, and a pound on > the suspension, and other weight in other areas, and now you can > downsize the engine and the transmission, and the brakes, and now the > fuel economy and the performance will go up. So the auto manufacturers > are always looking for ways to save weight which saves money and makes > the car work better. > An important function for the bypass hole is to insure that coolant > continues to circulate through the engine when the thermostat is closed. > If there was no coolant circulation before the thermostat opens there > would be localize overheating. This would occur in the cylinder head/s > around the combustion chambers. This would cause damage to the exhaust > valves and the cylinder head/s around the spark plug/s. The Mazda Wankel > Rotary engine has a very large bypass hole in the water pump housing. > 30% of the coolant is able to flow through this hole if the thermostat > is left out and this will cause the engine to overheat in hot > temperature. Most BMW, Mercedes, Audis, and Porsches will overheat in > moderate to high temperatures with out a thermostat. > Yes, the bypass hole also protects the water pump. If the coolant > wasn't able to flow cavitation would take place and this would quickly > damage the impeller and the housing. We had a Mazda RX-2 come in that > was eating water pump impellers. What I found out was that the owner had > been working on it and he had dropped a 4mm washer into the cooling > system. He looked for the washer but he couldn't find it. To get the > washer out I filled the engine full of water. I had made an adapter that > allowed me to connect a high pressure air line to the upper hose. When > the engine was full I turned the air line full on. I could hear the > washer fly across the shop and hit a wall on the other side of the shop. > The car quit eating water pumps. The previous paragraphs are fact. The > following paragraphs are my opinion. > Yes, names are all mixed up. The correct term for a prime mover > that burns some fuel to operate is an engine. Gas engine, diesel engine, > turbine engine, steam engine, and so forth. A prime mover that uses > electricity and has some type of armature that rotates is a motor. In > the US most 4 wheel vehicles are called either cars or automobiles. Yes > it is different in Europe. Technically it is wrong to refer to heat > engines as motors. It is technically wrong to refer to a motorcycle as a > motorcycle but it is clumsy to call them engine-cycles. But we call them > by the name motorcycle and that is ok. > In my opinion we should call motor oil just oil for it is used in a > lot of different situations. I don't care about calling motorcycles by > the name motorcycle but I do care about calling engines by the name > motor. We are supposed to be teaching the next generation and I feel > that we should teach them correctly. These are my opinions which I have > every right too. So please don't beat me up. I am not going to address > these topics any further. > I really enjoy the discussions as long as they stay civil and > friendly. Take care everyone. > Thanks, > rich! > > On 11/22/2014 3:25 PM, Bob Blick wrote: > > Changed the tag. Thanks Ariel for reminding me :) > > > > Yes and no. It all depends on the car. > > > > In a Miata, if you remove the thermostat, cylinder #4 runs much hotte= r > > than the others. If you are also flogging the car on a hot day, it's > > more likely to overheat because #4 boils and then you lose coolant an= d > > you're in trouble. > > > > The engine was originally designed for sideways mounting. When it was > > re-engineered for the Miata, they reversed the direction of the water > > flow, and a portion of the cooling for #4 became the heater core. The > > water flow was calculated based on the restriction of an open > > thermostat. With no thermostat, the flow is reduced through the heater > > core and #4. > > > > Lots of times when people turbocharge Miatas, they will re-plumb the > > cooling system to restore the originally-designed direction, and they > > get more even cooling that way. > > > > Bob > > > > > > On Sat, Nov 22, 2014, at 01:09 PM, Allen Mulvey wrote: > >> A motor vehicle engine does NOT run hot if you remove the thermostat. > >> > >>> -----Original Message----- > >> ... > >> > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .