Hello all, I am going to answer several different replies at the same time.=20 First of all to make the blanket statement that and I=20 quote, "A motor vehicle engine does NOT=20 run hot if you remove the thermostat." is incorrect as soon as it is=20 said. Yes, most of the iron duke engines that were being produced by=20 American manufacturers would not overheat if you ran them with out a=20 thermostat. The radiators were usually over-sized and the bypass holes=20 were small. So only 10-20% of the coolant flow would be bypassing the=20 radiator as the engine ran. If it was cool outside they wouldn't even=20 get up to operating temperature. This would cause poor engine=20 performance, excess fuel consumption, oil dilution, and poor heater=20 performance. Most European and some Japanese automobiles have engines that will=20 overheat if they are operated in moderate to high temperatures with out=20 a thermostat. The bypass hole can be large enough that up to 50% of the=20 coolant is flowing right back into the engine and it doesn't go through=20 the radiator. Also the radiators are engineered to be just large enough=20 to keep the engines cool in the highest possible temperature were the=20 car is expected to be operated. If the car is expected to always be=20 operated in the far northern or far southern latitudes it will possibly=20 have a smaller radiator than the same car that is expected to always be=20 operated in latitudes that are closer to the equator. Will an engine overheat with out a thermostat. It depends. The=20 thing about cars is that if you can save a pound on the cooling system,=20 and a pound on the electrical, and a pound on the body, and a pound on=20 the interior, then you can remove a pound on the frame, and a pound on=20 the suspension, and other weight in other areas, and now you can=20 downsize the engine and the transmission, and the brakes, and now the=20 fuel economy and the performance will go up. So the auto manufacturers=20 are always looking for ways to save weight which saves money and makes=20 the car work better. An important function for the bypass hole is to insure that coolant=20 continues to circulate through the engine when the thermostat is closed.=20 If there was no coolant circulation before the thermostat opens there=20 would be localize overheating. This would occur in the cylinder head/s=20 around the combustion chambers. This would cause damage to the exhaust=20 valves and the cylinder head/s around the spark plug/s. The Mazda Wankel=20 Rotary engine has a very large bypass hole in the water pump housing.=20 30% of the coolant is able to flow through this hole if the thermostat=20 is left out and this will cause the engine to overheat in hot=20 temperature. Most BMW, Mercedes, Audis, and Porsches will overheat in=20 moderate to high temperatures with out a thermostat. Yes, the bypass hole also protects the water pump. If the coolant=20 wasn't able to flow cavitation would take place and this would quickly=20 damage the impeller and the housing. We had a Mazda RX-2 come in that=20 was eating water pump impellers. What I found out was that the owner had=20 been working on it and he had dropped a 4mm washer into the cooling=20 system. He looked for the washer but he couldn't find it. To get the=20 washer out I filled the engine full of water. I had made an adapter that=20 allowed me to connect a high pressure air line to the upper hose. When=20 the engine was full I turned the air line full on. I could hear the=20 washer fly across the shop and hit a wall on the other side of the shop.=20 The car quit eating water pumps. The previous paragraphs are fact. The=20 following paragraphs are my opinion. Yes, names are all mixed up. The correct term for a prime mover=20 that burns some fuel to operate is an engine. Gas engine, diesel engine,=20 turbine engine, steam engine, and so forth. A prime mover that uses=20 electricity and has some type of armature that rotates is a motor. In=20 the US most 4 wheel vehicles are called either cars or automobiles. Yes=20 it is different in Europe. Technically it is wrong to refer to heat=20 engines as motors. It is technically wrong to refer to a motorcycle as a=20 motorcycle but it is clumsy to call them engine-cycles. But we call them=20 by the name motorcycle and that is ok. In my opinion we should call motor oil just oil for it is used in a=20 lot of different situations. I don't care about calling motorcycles by=20 the name motorcycle but I do care about calling engines by the name=20 motor. We are supposed to be teaching the next generation and I feel=20 that we should teach them correctly. These are my opinions which I have=20 every right too. So please don't beat me up. I am not going to address=20 these topics any further. I really enjoy the discussions as long as they stay civil and=20 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 hotter > 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 and > 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----- >> ... >> --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .