The laws of physics are what you apply as you experiment, hopefully safely and expecting rather predictable results.
I inadvertantly left out the thermostat in my 392 Hemi once. Never came close to over heating - never had any signs of heating problems at all - only notable observation I made was that it took MUCH LONGER to come up to temp.
In 1995 I had a 70 Chevelle with a stout sbc, th350, 12-bolt(373's) It had one of those Moroso restrictor's in it. The middle sized hole. Instead of a thermostat. I also studded the pulley and had no mechanical fan, just a powerful electric fan, and a stock chevelle 4-core rad. It would sit and idle forever in 90 degree heat and never go over 190-195 degrees. I couldn't get it to overheat. Last summer I had a 57 Chevy wagon with a 1976 350 in it. It kept heating up so I put one of those universal Summit Racing 2-core aluminum rads. in and punched the center out of the t-stat. That car would not go above 190, no matter the conditions. I drove it to Columbus GG's and cruised in m***ive traffic, nothing!!! Never above 190. And it was HOT! We stopped on the side of the highway 3 times for other cars overheating, and they were mad cuz I never even shut my wagon off. I have one of those $160. universal aluminum rads. waiting to go into my 53 suburban. I'm convinced.
This is a fun thread, and I learned something! I'm with Chuckspeed on his definition. Makes the most sense to me, and proved me wrong. Thats good stuff ! Its late, I'll see you all in the 5am part of the day...............
Well... I know from experiance that you won't win an argument with an engineer. To much education. But I have a flathead Ford that has two water pumps and an unpressurized cooling system. The faster I go the hotter it gets. No t-stats just restrictors. I know-I know, Flatheads and accepted physics theories are not applicable.
Oh well, guess my true iden***y is revealed - now let me go back to improve on gravity and finish creating this old universe.... So what happened to the original debate about an engine overheating without a thermostat? I like the educated explanations and enjoyed the lessons. My own personal engine cooling reality however shows very different results: Doing my own experiments I can run my engine for hours on the hot desert summer freeways or sit in traffic forever without any change to the temperature gauge, regardless of what I do with the thermostat or coolant of my cooling system. I tried various thermostat designs and temps, no thermostat, straight water, different water/antifreeze mix ratios and even waterless racing coolants. The coolant temperature is always the same, regardless. The only difference that was barely noticeable, was that with straight water and/or no thermostat, the engine was able to cool down a little quicker, after coming off the freeway. Definitely no overheating or higher temperature when running no thermostat. I don't want to dispute anything that has been explained here. These are just my personal findings and I have done countless test over the years. This summer I get to do the same tests with a fresh rebuilt 261 vs. my 20 year old daily 235. I'm very curious to find out how a new and old engine compares in terms of coolant temperature.
I have to disagree with those that say you can't move water through the radiator to fast to cool effectively. Yout theoretical rocket science is all nice and all but the transfer of heat doesn't take place instantly. It can, and in some case does move faster than the readiator can effectively cool it. A thermostat is for keeping it a constant tempature, but in some cases a certain thermostat's can be too restricitive. Haven't had one that isn't restrictive enough. Water is better unless it freezes where you are. Water Wetter can help but is no subs***ute for a proper cooling system.
Post 1968 Oldsmobile Rockets have a byp*** tube at the thremostat housing, from the block to the pump. Why?
All motors need some sort of a byp*** or release to keep water moving some until the thermostat opens. This is the Olds version. SBC's have a little port under the p***enger side W.P outlet to the deck surface, while BBC's have a hose from the front of the intake manifold to the water pump, mid 60's Pontiacs have a transfer from the intake to the timing cover, etc. You can plug these on a Drag car to even out water temps, but DON'T run a stat. I was experimenting with a big block Chevy that ran hot (BTW was NOT cured by adding a stat), and added a stat to my race car that had the byp*** plugged. Within seconds after starting, water was ******* out of the back plate gskt of my water pump. Don't think for a moment that a car's water pump doesn't have pressure! They do
I think Chuckspeed has a great point in all this. I like what he wrote. ***uming Chuckspeed has it spot on, there are still variables & why some engines can still get away w/o a t-stat. If you understand that the t-stat operates as a restriction to prevent the pump from cavitating, then many vehicles have a small enough upper radiator hose to also serve as a restriction - it may well be enough to work. This does not negate what Chuckspeed said - the restriction in these cases is coming from somewhere else (typically the upper radiator hose or t-stat housing), not the t-stat. I understand different things work on different cars & systems. I've had fairly similar engines in different applications respond to different things (some like T-stats, some didn't want anything, some wanted a t-stat w/o the center). There's always some restriction at the top end though - how much restriction is probably subject to some higher level math, but if it works in your application, you probably don't care about the math! The flathead is unique in that it introduces quite a lot of extra heat into the water due to the design of the exhaust ports running through the coolant (and why retarded timing really affects flatheads negatively more than other engines). Something else Chuckspeed said made me smile - the t-stat is the biggest pressure drop in a system. He must be an engineer! One of the most misunderstood principles is that of bernoulli - because it seems counter-intuitive to the average bear. If you put your finger over the end of the hose & make a small stream, it shoots farther - but pressure is lower - it's just the flow is faster. If you put your hand in front of that stream, it hits it harder, so intuitively, you think it's higher pressure, but it's just the water going faster - the pressure is definitely lower.
I love this, I post a thread yesterday, go to work and leave it alone. At lunch today, and its still on the front page! I appreciate some of more applicable ****ysis here. Localized boiling is certainly a problem that some specific engine designs may have, and using a restrictor downstream of the pump to raise the pressure will help in that case. However, when you talk about cavitation, a thermostat or restrictor will raise the head pressure required for the pump w/o affecting the feed pressure - this would tend to increase cavitation. The only solution to this is to slow the pump down or raise the feed pressure relative to the head pressure. I think oversped waterpumps are responsible for a lot of this myth. People think that the coolant was "flowing too fast" to effectively cool, when in fact the pump was just cavitating the **** out of the water and resulting in a very low net flow. That is why some people find success in changing their WP pulley size to slow it down at higher RPM. That verywell could have been part of my problem on the ranchero, but I dobt it. Im glad to see that those who truly understand what is going on and how the system works generally agree with me. For those of you who keep insisting that linger time is a factor I hate to tell you, but you are just wrong. Anyways, great debate. I am happy to be at least partially vindicated by chuckspeed and flaternie a****st others. I was having problems with my ranchero overheating on the freeway... everyone insisted it was because I was not running a thermostat. As much of an ego hit as it was, I finally conceeded and threw a thermostat in. Much to my surprise (not) it continued to overheat just as it had before. Summit Al radiator solved that problem, still running a thermostat tho but I can't get the damn thing to come up to temperature now. Anyway, Rage on - Im glad this hasnt turned into a flame way apart from the few offhand comments about engineers or Rocket science. But thats fine, Ill just take your comments with my paycheck and you can keep yours. By the way, the last cooling system I designed was for a 500 lb thrust engine. It generated 3 MW of thermal energy - thats about 4000 Horsepower. The whole engine weights about 8 lbs. Now Thats power to weight
where's" MR WIZARD" OR "BILL NYE THE SCIENCE GUY" when you really need them? the transfer rate of btu's ?????
Yep, and how about plug flow and laminar vs turbulent in the radiator Dr. Bort? My guess is that "Q" generated by the engine can increase, yet "Q" rejected by the radiator (for a given ambient & airflow) has an upper limit. Seems that Chuckspeed offered a sound reason that may explain it. Otherwise we get back into weighing whether high coolant flow rates may affect the radiator's performance? In my own case, the coupe's SBC would never warm up when I ran w/no thermostat, the minute I put one in, bingo! right up to 190 degrees and stayed there. So it would seem to disprove in this particular application, the wives' tale.
Yeah, that would be the easy way to explain that one away....haha I got a brand new gauge, tube and sender. And the old one showed exactly the same numbers. I am anything but a pro engineer, but I've been driving this engine and truck daily for 12 years, in over 110 degrees and below 30, depending on the season. With all the interesting theories that have been presented, I had to mention what my personal findings are. In fact driving without a thermostat once for 2 hours on the freeway kept the engine at 150 degrees and falling with the outside temp drop at night in the desert. Never again - you need to maintain the minimum temp regardless.
You arent really grasping the point, so I can't really answer your question because it doesn't make sense. If the temperature is constant, then Engine heat output = radiator heat output. It has to be.
I run a 160 degree stat in my '80 Turbo T/A. It's carbed but the lower operating temp helps keep spark knock under boost down and prevents the computer from pulling timing and dropping power. I have to put a 180 back in to p*** emissions testing though. The factory had a 210 IIRC. Also, in regard to heat transfer, you're forgetting that it is being transfered out in two stages, water to br*** (or aluminum) and then br*** to air. I'm sure br*** and aluminum have different heat transfer rates, not to mention air itself is a damn good insulator. Transfer in and out will be at different rates (I think) because you transfer heat from cast iron to water and then transfer out from water to br***. The two metals must transfer heat at different rates. Shawn
I just discovered this old thread and would like to add my two cents worth. Like Bort62, I never bought the theory that slowing down the water flow would make an engine run cooler. It just doesn't make sense. I ***umed that if thermostats or restrictors did play a role in preventing overheating it would be because of the effect that Flat Ernie describes, where a pressure increase caused by the pump working against a restrictor raises the boiling point and helps prevent localised boiling in the heads. What I think happens when water boils in the heads is that it expands rapidly as it turns to steam and this expansion forces water out of the radiator overflow, and the engine then overheats due to lack of water. Using a restrictor in place of a thermostat is common practice in race car engines for two reasons. Carroll Smith mentions them in one of his ------ To Win books (I forget which one). One reason is to eliminate the thermostat as a potential source of trouble and the reason for installing a restrictor in its place is to generate "block pressure" to prevent boiling and steam pockets forming in the engine. I did a test a while ago on my 59A flathead to find out what kind of pressure is created by the water pumps. I plumbed a pressure gauge into one of the heads just below the thermostat and then, with the engine at operating temp and the thermostats wide open, slowly raised the revs while watching the gauge. No pressure registered until 3000 rpm after which it built rapidly to a peak of 20 psi at 5000. This would raise the boiling point to around 272 degrees fahrenheit. It seems plausible that this might prevent overheating in a race car running at constant high revs but would be of little or no benefit in a street driven flathead which would rarely exceed 3000 rpm. Evidence that slowing down the water flow doesn't improve cooling can be found by visiting Davies Craig's web site daviescraig.com.au and watching the EWP DEMO. Briefly, they set up a test using their electric water pumps to measure the relationship between water flow rates and heat rejection from a radiator. The relationship was linear (the faster the flow, the more heat was removed) up to a point and past that point further increases in flow didn't give a commensurate increase in heat rejection. Note that circulating the water too fast didn't increase the cooling much but it didn't make it worse either. It follows then that if speeding up the water flow doesn't make cooling worse, then slowing it down won't make it better. This whole thread makes interesting reading and I can't help wondering if some people would rather trade folklore and supers***ion than learn things that will help them make their cars run well. It starts with a well-reasoned post by someone who obviously knows their stuff. Some other knowledgeable people such as Chuckspeed and Flat Ernie chip in, but some of the posts demonstrate just how much ignorance and confusion there is out there about how cooling systems work. One poster even implies that flatheads don't obey the normal laws of physics!
If the fluid is moving thru the radiator too fast to remove the heat, it is also moving too fast thru the block to absorb ALL the heat and the block temp rises.
I had a 49 ford pickup with a 289 ford engine and a final drive ratio of 4.27 to one. This thing was twisting about 3500-4000 rpms at 65 MPH and it would invariably overheat out on the highway...after running for about 5 minutes..ran cool in town and at idle. The radiator was an old verticle flow br*** and copper dodge pickup unit...plenty of airflow to it and with the stock hood side-vents it had plenty of air out-flow. My dad said it sounded like a cl***ic case of missing T-stat so I checked...sure enough, no thermostat in the hole. I put in a 180 degree 'stat and never had a problem with overheating again. No, I did not pump the water out causing overheating as has been suggested here. Cavitation would have been a problem regardless of having a thermostat or not so I have to disregard that. The only conclusion I can come to is the coolant was indeed p***ing throuogh the radiator too rapidly to get sufficently cooled before it was reintroduced to the engine...and I'll believe that until somebody can prove it wrong.
Not necessarily. Lack of a thermostat causes the water velocity to increase, and that causes the pressure drop thru the radiator to increase. Higher pressure drop thru the radiator decreases the NPSH (net positive suction head) available at the pump inlet, setting up the exact conditions required for cavitation. It'd be interesting to get a flowmeter into the top radiator hose on some of these engines that overheat without a thermostat. I'd suspect it would show the flow rate is actually decreased rather than increased.
Actually back to back drag racing Pontiac's have proven that running a 160 stat Vs a stock 185 stat is good for 1/10 of a second in the 1/4. Thats proven track tests over and over. I think this is just due to a denser air fuel mix. I run 160 stats in all my cars and have great heat in the winter with them. I also can sit in traffic all day long when it in the mid 90s air temp but it has to be at least 140 on the pavement. I run 4 core radiators and a good shroud with good water pump plate clearances with stock 5 blade power flex fans that sit halfway into the shroud and run a tad rich on the wide band O2 sensor. This is all text book for running cool. The hottest I ever see my 12 second street car is 175 degrees. So I guess my question would be, why take your thermostat out? If you are over heating, fix your cooling system and or engine mechanicals .
I haven't read all the posts, so maybe this has already been suggested. Since thermostates do restrict flow, running without one increases flow. I could see a potential of cavitating the pump due to starvation. This in turn could froth the coolant, which would result in the potential of air pockets plus a less dense fluid that would be harder to pump. Just a thought. We actually see a similar issue with the (9) 1250 Gallon/minute pumps on our machining lines - we can actually displace so much coolant from our coolant pit under certain demand conditions that the pumps cavitate, which in turn creates foam. We lose header pressure and have to treat the coolant and wait for the foam to dissipate.
x2 a thermostat only comes into the equation when the temp is below its operating temp.plus im sure the coolant is metered through the water pump.so many gallons per minute.plus the way you are explaining the cooling system, why does a car seem to cool better while moving instead of sitting still running
Yes metlmunchr, That would be interesting. There are other possibilities for why putting a thermostat in could fix overheating. When the radiator core restricts the flow into the pump, the lower NPSH (thanks for that term guys) might **** the bottom hose(s) flat at high revs (seen it happen), restricting flow and causing overheating. Installing a thermostat might cure this condition, leading the installer to believe he'd cured the overheating by slowing down the water flow when in fact he'd inadvertently sped it up.
Does this not disprove your theory? The heat transfered is ***ulative, so the heat will increase. Hold your hand in for one second, then do it for ten and tell me it's the same result. I had an overheating flathead Ford and installed restrictive washers, end of overheating. I been around long enough to know what works on paper does not always work in the real world.
i've seen restrictor washers work to lower temps ...but only on flat head fords. could this be because it forces the water to byp*** back through the engine to homogenize the temps from the rear cylinders to the front?
Like any engineering problem there are many solutions. The size and shape of the radiator is determined by several factors, space available, cooling requirements, air flow availability. The thermostat's job is to restrict water flow until a pre-determined temperature is reached and maintained at that temperature by restricting water flow by opening and closing.
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