I think there is no straight answer as there are so many combinations of different parts and motors. My straight axle nova runs hot(190-200+). It has a two-core (two inch cores) aluminum radiator (biggest rad you can fit between the frame rails), a aluminum hi-volume Weiand pump, A Moroso "Tuned" 180' thermostat, 18" flex fan with shroud, on a aluminum-head 427 (and yes, the timing is right, 38' total with 8" initial). The addition of the shroud made NO difference. I've done a bunch of reading before deciding what do do next (I.E. what to buy/change). My belief in my combination is that the thermostat is impeding the flow to the extent that the water heat transfer from the block is overcoming the amount of heat transfer from the radiator, which I believe from the cooling surface area (the key point) can handle more flow. I'm doing this today, so the answer will be soon.... I work on cars for a living, and I can tell you positively (speaking about cars of the last 40 ys or so) removing a thermostat (or having one stuck open) will cause the vehicle to run cooler. I've seen many cases of gutted thermostats (or none) to hide the fact of overheating problems in cars sold at "Wholesale" lots. That being said, there is no "bottom line" solution with the many systems people have here....
I've also noticed over the last few years that buying a new thermostat gives you a good chance of getting one that's junk. I replaced the one in my daily driver pickup's 4.3L V-6 3 times before I got a good one. The rest of them would hunt (stay shut until well above the 190* rating then fly full open and stay there until the temp drops to about 150*,and repeat in a never ending loop). I thought maybe it was just bad luck until I was talking with a guy at the parts house a while back who's run his own garage for about 40 years. He said he'd guess about 1 of every 4 stats he gets now is no good, and it started about the same time as when most parts like this started coming in from China and Mexico.
I have cured the thermostat problem by removing the thermostat, water pump, filling the block with block filler, running solid aluminum heads, and injecting mass quantities of nitro and a touch of alky. No more pesky boiling water.
i like the hand through the flame thing, but that's a candle, i have ran a few cars without a stat, and they did okay, i think it comes down to how big the radiator and motor is, like you wont get burned if ya pass your hand quickly over a candle, but try that with a blow torch, and then run it through some liquid nitrogen.. its gonna burn then freeze, whats the difference? amount of heat / cold. so i think it has something to do with that....
yep that's how I always thought a thermostat worked. interestingly when you run a remote electric water pump, they recommend removing the Thermostat and using a controller that varies the flow, in this case the controller does not flow water until a preset operating temperature is reached. Then the controller will adjust flow rate according to temp.- less at normal operating temp. - more at higher temps. .. .
30 some years ago I had a dirt stock car with a Ford FE engine. I was not running a thermostat, and I was having overheating problems. An older, uneducated but very intelligent buddy of mine kept telling me the water was flowing through the radiator too fast. He couldn't really give me what I thought was a good explanation as to why the unrestricted flow was a bad thing so I resisted taking his advice. I had a big 4 core cross flow radiator. I tried a few different shrouds, went to a smaller pulley on the water pump. The thing still ran hot. At my friend's insistence I added a 1" washer as a restrictor in the t-stat housing. Operating temp dropped considerably! Several years later I raced a 300 Ford six. I originally ran it with a restrictor and temps were in the 180 range. For shits and giggles I removed the restrictor. It did run hotter, but still only in the 190-195 range so I left the restrictor out. It did take much longer to bring it up to operating temp. I've seen the hose clamp on the radiator hose trick too. No engineering degree, no formal education beyond high school, just real world "school of life" experience.
I'll just re-quote this, as it is the definitive answer, and save y'all from digging thru all the posts! You're very welcome
I worked in Thermodynamics lab for AMC JEEP for 8 years. Cooling system performance was always tested with the thermostat blocked open to the max open position. We ran the engine,or complete vehicle at max throttle,and max load until the temp stabilized. We then could calculate the max "Air to Boil Temp". You must remember that the stat only determines the MIN operating temp.
I think that theoretically you are correct in making the postulation that the cooling liquid will cool just as well moving faster than slower. Unfortunately in a world of mathematics there are always exceptions to the rule. Look at it this way, Algebraically taken known entities I can prove beyond a shadow of a doubt that in the year 2025 a man can run a mile in zero seconds. Given the same knowns I can even prove that eventually a man can run a mile in less than zero seconds. We live and work in a finite world we have yet to find anything that cac function in negative time. I said all that to say this, you can crunch numbers all day and come up with calculations that look good on paper but in the physical world or in practical application they just don't fly. Now consider that when you are cooling an internal combustion engine that it is not how fast the water moves through the radiator that you are considering. It is in fact how fast the coolant is moving though the engine block and heads. The majority of the engine blocks that we work with are made from cast iron. They are not forged or even shot cast but sand cast. Sand casting leaves imperfections, voids, fissures and etc. Now take into consideration that your engine block is a huge heat sink. Cast iron does not transfer heat well, but by nature retains heat. What we are trying to accomplish is constant contact with the material that we are removing heat from. By slowing the coolant down it has more time to make contact with the cast iron and with all its nooks and crannies. The thermostat holds the coolant in the block until it reaches a set temperature then it opens and allows new coolant to move into the block and once the cooler liquid reaches a saturation point and hits the thermostat the stat closes and the process begins all over. If all is functioning properly we maintain a constant heat or what we commonly call operateing temperature. It is primitive compared to what you normally work with but you have to realize that we are using a primitive method with primitive materials. The fact is that it works to help maintain a constant temperature. If you are looking at a race engine a lot of the time a thermostat is not used at all. This is an engine that is not going to have to set idle for a time and have constant load and unload conditions. It is common for a race engine to use a restrictor in place of the thermostat. It looks like a washer and is nothing more than an orifice that is designed to control the flow of coolant. That is an entirely different arguement all together. Perhaps it is not at all in line with the thermostate debate, never the less it is most likely what you are accustomed to working with.
I haven't read the whole thread, but I will inject real world experience. This is Dodge diesel Cummings 24 valve bumped up to about 325hp. I noticed while towing that on long grades if I kept in OD 1900 rpm I ran 190°. If I dropped to 3rd and 2400 rpm the temp would run about 210-220. It was time to change therostat and a new one from Dodge purchased. The first thing noticed was the open orfice was about 2/3rds the size of the original. New one installed and the 2400 rpm temp ran the same as 1900 rpm. J
@ Bort62 A Sprint Cup car does not run a thermostat. Waterpump speed is around 42% of engine speed, flowing around 52gph. It uses grill opening size to control water temperature. All that being said...it depends on the application. Some things run hotter than others, some things run cooler...
So what happens when the water in the radiator cools the water below the thermostat temp? It closes. Then while its closed heat transfers to the water. Once its to temperature it opens and cooler water is brought in. Since the water flow stops when the t/stat closes it spends more time in the radiator cooling off. If the water doesnt cool to below the tstat temp it just stays open and it runs at a hotter temp then the tstat and could then over heat. or could not. Ive had a few cars and a jeep that overheated then when i went to change the tstat there wasnt one. Ive added them and then been fine. Im drawing my own conclusions useing the scientific method.
That's always been my question. Just think of the amount of money the manufacturers would save by eliminating the thermostat. As for all of the equations, math calculations,and theories, aerodynamicists have proven that a bumble bee can't fly but nobody has ever bothered to tell that to the bee.
"It is considered common knowledge around the hotrod community that running without a thermostat may cause overheating. The reason quoted for this is that the coolant moves through the radiator too fast to properly cool." You also answered your own question...it MAY cause overheating and the radiator design for that application MIGHT be wrong...
What debate. It takes 2 to debate. I've never built a car without one and I can't for the life of me understand why anybody would want to. The only car that I ever built thjat I thought had an overheating problem turned out to be a mis-matched gauge and sender. I heard all the flathead myths. I used them anyway (Ford did) ...not a problem I did opt for a 160 stat for my 34 using an original radiator in front of my Studebaker engine. I should have gone with the 180. In the spring it doesn't want to run where I like it. 180-200 area depending on the day. There is nothing to debate for me. If it was good enough for Henry and GM, it's good enough for me. I personally believe that most problems come up when people go off the deep end chasing wives tales instead of fixing what ever the real problem is. Too many old wives tale remedies turn into wild goose chases. You guys can argue theory all you want. I'll just drive mine.
Where does your calculation take into effect the variable amount of water through the radiator (as water is pushed through the water pump as a function of engine RPM), and where does your calculation take into effect the volume of air moving across the radiator? This volume, of course, being widely variable, as it is sometimes driven only by the cooling fan (which is a variable speed itself, depending on engine RPM), or air driven through the radiator by vehicle speed. Your postulation seems to assume constant speeds, and constant quantities of coolant through the radiator and engine, and constant volume of air across the radiator. -Brad
Since we are in this debate about cooling internal combustion engines I have a question. I always thought a radiator only had one core made up of rows of any number of rows of cooling fins/tubes. stacked one behind the other. This package of rows of colling fins/tubes makes up the core. A radiator can only have one core? Right? I always said my radiator has a four row core not four cores. But then I don't build radiators for a living. I just use them.
I have had good luck using Ford's diesel coolant system additive and maintaining proper ph along with a 50/50 coolant mix.
Chuck has it right. Without a tstat you can't regulate the system to an optimal operating range. You may manage to keep a motor 'cool enough' by oversizing the heat exchanger but is that really what you want? Would you be able to maintain constant operating temp regardless of condition? (ie driving slow/fast, up a hill, stop&go, high/low ambient temp, variable power (continually changing Qengine) etc) My guess would be without some sort of flow regulator your engine temp will be all over the place. The tstat is there to cover the variety of conditions the system faces. It forces the engine to remain at constant temp.....or at least makes a valiant effort. Even the best regulated systems can overheat if you push them too far. Take the ride in my avatar for example. It has a 180 deg stat and it will stay there all damn day as long as you have enough air moving over the radiator to remove the heat. (It also runs like a sick dog unless its up to temp so there is an optimal temp range for performance as well) Take away the airflow and suddenly we have found ourselves in a hot situation!
Chuckspeed gets my vote....Now if you have a 160° [or any other value] when should it start to open? I think the actual temperature range from start to full open is actually pretty small, like maybe 10°, and at full open it is the rest of the componets responsibility for flow rate? Guess I'll wait till the wife leaves and borrow one of her pots and the stove and do an experiment..
My 70 torino with a 351 cleavland has a factory crossflow rad and it also has a restrictor in the thermostat housing. Told never to loose that restrictor if it's ever taken apart. So factory used a restrictor woth a cross flow.
You are correct. Many fluid (water or air) pumps require a certain amount of back pressure (head) or the motor will overload. Just this week I had a problem cooling some 2,000 hp electric motors because someone turns the cooling fan speed up too high causing it to cavitate. I had to set up an air flow meter to show them that the flow actually reduces when the speed is increased. They also like to open doors in the room which lowers the back pressure and allows the fan to cavitate.
it's been interesting reading all the different things people have learned from auto shop to college to grand pappy's garage. i really think that a lot of this has to do with what engine, water pump and radiator you are running. if the radiator is a very small one like on older cars, with not so many feet of tubing, then you very well could experience water going so fast that it doesn't cool as much on the way through. if you run a oversized 4 core desert radiator on the V8 Merc, then you probably could never get enough flow from the water pump to measure the difference. i have run cars with and without. right now my 4 banger rice burner is running without, simple because i have a blown head gasket. the car seems to run the same temp on the factory gauge as when the thermostat was in there. i'm running a loose cap too. on my '65 GTO 389 i ran without one for a while and the Stewart Warner gauge ran noticeably cooler. as to this flow issue... it is my experience that when you remove the thermostat, you lose the pressure at the thermostat, but the volume going through the top hose stays pretty much the same. the water flowing by the radiator cap hole surly is flying by at breakneck speed. a water pump is designed for volume, not necessarily pressure. the paddle wheels and sometimes turbine looking fins are not really sealed, forcing water on forward like an oil pump with its gear design. my thought is this: if the water is heated to say, 180, before letting the water flow to the radiator, there is more heat going into the water in the block before it moves along. 180 at the thermostat means boiling temps at the cylinder wall of the block... thus the 15 psi radiator cap. running open lines with the thermostat out would have the water circulating all the time, leaving lower temps to start with, thus lower temps at the radiator to have to cool in the first place. IF the water has less temp drop, then the increased flow means LESS heat going into the water in the block as well, as said before, it's a push. looking at all sides of the issue, i think someone back when on one of their cars had a heating problem and blamed it on the lack of thermostat and the rest is a fishing story. personal experience or someone trusted (in their eyes) telling them something is going to be the "standard" for the rest of their lives. it's like my ex... she calls me one day and says "I need you to come change the thermostat on my car"... I asked "Why, it's been running where it's supposed to". "Yes, but I have been loosing water".................. ooooooookaaaaaaay???? "But it's inside the manifold and i cant see a leak there" "Well I had a pickup years ago and when I changed the thermostat, I stopped loosing water". she also told me once to please change the shocks on her car... "Why, they are only a year old".... "Well, because the car is riding too low"................ ooooooooookaaaaaaaayy???? "Hunny, did you know that the "springs" held the car off the ground and that the "shock absorbers" do not lift the car??" "Yes, but my cousin the mechanic said that's what I needed to do". Folks, you can't argue with logic when it's in someone else's head. You can't change someones mind when they think you are far below their own personal experience or when Cousin Vinny says so. You know what I did? I changed her thermostat with her help handing me tools. When the water leak was bad enough to smell coolant coming in the window at a traffic light, then she panicked and brought the car over again. I showed her the coolant leaking from the hole in the water pump and told her (at Easter) that her water pump had 2 weeks to 2 months to live. she drove the car putting in water every day. drove it down to thanksgiving. while picking up a friend from the airport, her engine overheated and cracked BOTH heads and oil was coming out the tail pipe. i told her "you better wise up, because i am not going to give you free labor so you can ignore things to the point that it costs us a ton of money and my time away from other projects." she was gone in hours, had AAA tow the car away. i never saw her again. i haven't had to put up with old wives tails since then, nor her thinking that good cooking was to smother everything in a gallon of olive oil either! (sorry, still pissed) i drift back to the flow thought... this is a no brainer. get two 55 gallon drums. fill one ½ full. extend the lower radiator hose to the drum with water. run your top hose to the empty drum. start your engine and time how long it takes to pump the water to the other drum. turn the engine off and let it completely cool whilst you remove your thermostat. now pump the water back to the other drum and time it again. now you can compare the flow with and without the thermostat. "But wait! Wont my engine overheat while waiting for the water to get to 180?" Not if you open the top housing, block an old thermostat open, and install it for the "IN" portion of the test. you will have the engine shut off before it gets hot. We're only talking about pumping 20 gallons of water. please post your results. maybe we can get MITH BUSTERS to test it too. TTFN
Two of my friends are on the shop crew, and one is a former on-camera talent. I will see if they will lobby for it.
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