The Stovebolt Site Forums The Shop Area Engine Shop What is water temp without a thermostat installed?

My kid is considering running his 6 cyl jeep without a thermostat. What will the water temp. be if he does it and is it safe? Thanks

Scott

He shouldn,t do it. It controls the flow of coolant. Too much flow can cause overheating. The temp. may vary acording to the temp. outside & the cooling system effeciancy. Running to cool reduces gas mileage & delutes the oil.

[ What will the water temp be? ]

UNCONTROLLED !!

I once had a '75 Hornet with a 232 or so. The thermostat stuck closed when I was far away from anywhere. I took the thermostat out to get back home but then goofed around and didn't get a new one installed for some time. I was probably screwing up the engine but I quit using oil.

There is no science to justify the idea that too much water flow results in overheating. It is an urban myth. I have run my 302 without a thermostat and it simply runs cold. Too cold. Engine wear is less at a normal operating temperature.

Doesn't have to be science involved. Common sense tells me that the newer vehicles have smaller radiators in comparison to the older ones who ran low cap pressure.

My old 58 Chevy seems to do okay without the thermostat, but if I take it out of my Caravan, it runs hot after a few miles. (very small radiator, and coolant moving very fast simply hasn't got enough time to cool) Read this on a tech sheet at work one time too, though don't remember the exact words.

Either way, too cold or too hot, is not good. Too much wear, too poor running, too poor of fuel economy, etc. My experience has been too cold, but mainly in the Wisconsin winters......Roy is right though, and so is science.....not enough time for the heat exchange to take place can result in overheating, with a radiator that was designed for lower flow rates. High flow rates can result in too cool of an engine if the radiator is oversized. The engine should be warm enough to get any condensation to evaporate out of the oil, too.

This topic has been discussed ad nasuem both on this board and throughout the internet. I did an extensive search on the internet, asked professors, a nuclear sub engineer and they all said the same: high flow rates do not cause overheating.

Here are some excerpts from that internet search:

The thermostat temperature shouldn't matter if the equilibrated
temp is higher than the thermostat temp, i.e. once the thermostat
is open it no longer affects the temperature.

I'm no expert on this stuff, but with regard to your question 2)
I believe you want the flow to be as high as possible (qualifications
below). The important thing to note is that the average temperature
of the coolant is independent of the flow rate. If the flow is 0
then the engine is putting infinite heat into the coolant it
contains, and the radiator is removing no heat from the coolant it
contains. At the other extreme we have infinite flow. In this case
the engine adds 0 heat to each unit of coolant that passes through
it, and the radiator removes 0 heat. In other words the temperature
increase across the engine is 0 and the drop across the radiator
is 0, so all of the coolant is at the same temperature. Obviously
this situation is unattainable, but you want to get as close to it
as possible. Why? Because higher flow reduces the maximum temperature
of the coolant, so you reduce the chance of steam formation. So,
what are the drawbacks to high flow. First, you have to worry about
turbulence. I believe some turbulence is good because it breaks up
the steam layers that form on the engine surfaces, but I imagine
that too much is bad and it screws up the simple model I described
above. Second, if you try to drive your water pump too fast it will
cavitate, leading to reduced flow.

And finally, ethylene glycol may raise your boiling point, but it
also reduces the specific gravity of the coolant. This means that
not only CAN your engine run at a hotter temp but it WILL run at
a hotter temp. It would be interesting to know what the break-even
point is. I imagine one should determine how hot they want their
engine to run, then put in just enough glycol to ensure the coolant
doesn't boil at that temp.

Enough rambling for now.


In general, (a) is correct. Don't think about individual hunks of water; think about heat transfer out of the radiator. The radiator is most efficient when it is at a high temperature compared to the surrouding air that's blowing over it. Thus, the faster the water goes (and the higher the exit temperature), the more heat the radiator dumps per unit time. The limit is reached when the temperature of the water is the same as the temperature of the engine, and each little hunk of water only carries an infinitesimal amount of heat on each (very fast) trip.


Sorry, but that doesn't mean anything. Your statements about heat transfer
are true regardless of whether the thermostat is installed.

Also, many people have experienced overheating (after removing the
thermostat) under normal driving conditions. If increased flow rate was
responsible for the overheating, then cars should overheat if you drive at
normal speeds in too low a gear. That will increase the water pump speed
and increase the coolant flow rate without a corresponding increase in
airflow through the radiator.

But in practice, production cars will not overheat even if you drive around
in low gear. That's another indication that high coolant flow rate does
*not* cause overheating. In fact, high flow rates increase heat transfer
due to increased turbulence.

Physics conflicts with 'horse sense' in this case. Regardless of the
composition or thickness of the surfaces involved or the type of coolant, in an
automotive cooling system the faster the coolant flows thru the system the more
heat will be transferred.

My source: "An Engineering Analysis of Automotive Cooling Systems", a four-part
series in Skinned Knuckles magazine beginning in November 1990. Automotive
engineer Bill McLellan specifically analyzed Ford cooling systems, and used
hydraulic equations to deal with the questions of flow rate and water vs an
anti-freeze mix as a coolant.

Before I let this dead horse rest in peace, I'll take a few more whacks.
I have been running cooling system simulations. For any given heat input to the water jacket, and
radiator with constant characteristics, if the quantity of coolant flow is increased its temperature
drops. By coolant temperature, I mean at the thermostat location, the radiator outlet, and the
radiator average temps increase. This applies to cold start & run-up to temperature, with high flow
run vs. low flow run, and hot running with a sudden change of flow. Except for brief transient
fluctuations, the coolant temperature is always lower with higher flow. If the radiator is just big
enough for a certain heat input, (I.E. the coolant will overheat with any increase in input) its
capacity will increase with a higher flow.

"More flow = cooler engine, period."


The idea that it will run hotter is flawed. Elementary Thermodynamics,
higher flow = higher heat transfer. You may even get discussion about laminar
and turbulent flow, bla, bla, bla. The water pump generates plenty of turbulence
and the paths through the engine are quite narrow anyway.

However, with the thermostat out, if you drive under "severe service"
conditions, not letting the temperature come up and stay up before shutting it
off, you may need to change your oil more often. The contaminants (acids, water,
etc.) will not have time at temp to boil off, possibly causing accelerated
engine wear.

Also, although a lower temperature will enable you to advance the timing a
little further (if you are only making short runs, if the engine comes up to
temp, this will result in detonantion) and get a cooler, denser air/fuel charge,
this will NEHATIVELY effect efficiency; power will increase slightly during the
warm-up period, mileage will decrease, more than slightly during the warm-up
period.

The engine will still run the same after warm-up, which of course will take
longer without the thermostat. My advice, don't drive a STREET car without a
thermostat, unless the one you have is stuck closed and you have to take it out
to use the car to go get a new one . . .

Totally agree with Jason.

Just need to add that modern "compukerized" autos will use more fuel at lower temps.

And can't help wondering WHY you would want to run without this least expensive part of your automobile.

Reo-guy,

Sure, adding ethylene glycol lowers the specific gravity but didn't you mean to say it lowers the heat capacity and, in turn, lowers the efficiency of heat transfer?

Science or not , my dodge van began running much cooler one day this winter. Almost no heat with heater wide open. The cause? A broken thermostat that caused it to lock open. Put in a new one, and the running temp returned to normal and I had heat once again.

My thinking was flawed. Must have been the barley pop while workin' in the shop. I was thinking if the radiator was too small it could overheat with no thermostat, but then it would also overheat with one in. I can admit when I'm wrong!

You guys are all missing the important questions here. Why is your son thinking of running without the Thermostat? Is the jeep running Hot? Is the stat stuck open/closed? Why?

Let us know that and then we can better answer the question.

It has been scientificly proven that a bumblebees and wild turkey cannot fly. They do. Just as bublebees fly, engines are more likely to overheat without thermostats. The statement more flow cooler engine seems correct the way it was presented but it ignores some factors not presented. Consider this, the engine depends on the coolant,oil,octane of fuel,timing,type of metal,thickness of metal, shape of metal,air flow around said metal,the engine compartment itself and last but not least ambiant temperature. Designers through the years have engineered these engines to keep a delicate balance of all these factors and more. We benifit today from one hundred years of trial and error.
I'll use two engine types to make my point. The Model T was equipped with a 4cyl engine that had no water pump. It relied on convection to move the water through the engine. As the engine block heated hot water would rise into the radiator from the engine block this forced the cooler water down through the radaitor into the the block, a circle. In conjunction with oil airflow temp. ect ect. the engine functioned well for 1908. Look at 1908. Rural areas,rough roads with little traffic,and longer trips with fewer stops. By 1927 problems were beginning to show. Model Ts had a tendancy to run hot and boil over in the summer especially in cities and urban areas. Why? Look at 1927. Stoplights, heavy traffic in the city,pavement,Shorter distances but more time driving due to traffic. Why did the T overheat? It was not designed to function in stop and go traffic on Mainstreet in July. The balance was upset. The cooling system could not cope. The convection that worked so well in 1908 could not overcome the change in driving habits. The engine block heated the water normal convection began but due to the reduction of air flow the water became super heated because it stayed too long in the block. The hotter radaitor I'm sure was removing more BTUs "heat" but it was not enough. The longer it ran the hotter it got. What helped fix this problem the waterpump and then the thermostat.The water pump cooled the engine a great deal but it became cold natured in winter and still would over heat at times in the summer. To explain the thermostat I will use a later engine known for it's overheating problems the flathead V8. Truthfully the flathead was designed for running in the cold Dearborn winters at 10 below. At at 100 in the summer the flathead had to be driven carefully to keep from overheating even brand new factory fresh with all the bells and whistles. Hotrodders at first blamed the thermostat and removed it. It seemed to run cooler for a while but it seemed to get even hotter the longer the engine ran. Why? The balance was upset. The dual water pumps and massive raiators of the flathead were designed to keep that hot running engine cool. The pumps flowed massive amounts of water. It took longer to overheat but it still would overheat. The superheated water comming from the pumps so fast they went through the massive radiator with no time to cool properly. This was OK until the whole volume of water became overheated and could no longer remove the excess heat from the block. The radiator even though hotter and removing more BTUs was losing the battle to the superheated block. A circle. In this case without a thermostat the water was moving to fast and overheating. The exact opposite of what happened to the convection cooled Model T. Same same but different. The hot rodders solution was a flat washer in the thermostat housing with a one half inch hole. This gave enough restriction to let the radiator do its job. Most of the time this cured the problem. It's that delicate balance again. The thermostat slows the water down a little even when it is fully open. It is documented that racing engines of the flathead era did better and did not overheat as much with the washer than without.

Thanks for all of your replies! I had no idea it would creat this much discussion. As to the reason for removing the thermostat.... He has a 49 Willys Overland. He was thinking of driving from here in central Wisconsin to Puebla Mexico with it to take a required language class during this summer. He wants to tow his friend's 350 motorcycle on a 2 wheel trailer. He has been having temp problems. The temp runs just below the "hot" mark on his gauge. He is studying to be a mechanical engineer, and I can't tell him much he doesn't already know. He seemed surprised when I suggested taking the stat out to see how low the temp could get and to get some good flow while trying to clean out the cooling system. Since I asked the board this question, he took it on a trip of 100 miles and blew the head gasket. Better now than in Mexico.

His water temp was running at 160 degrees. In order to know if the cooling system is cleaned out and performing well, I figured that if we knew what an "average" engine's water temp was without a stat, we would know if we had it cleaned out. Anybody have a ball park on that number?

If he got into the mountains, pulling even a small trailer, in a hot country, he would be s.o.o.l.

He needs Spanish to graduate next spring and has a "girl that is a friend" that is going to school in this town near Mexico City. ....I know, I know, but think of what you were doing at that age. Thanks again - Scott

Well I think I would fix the head gasket and put in a 160 degree stat. If he want to run cooler (after flushing the rad and block) try losening the rad cap a bit or go to a lower poundage cap. Good luck!

Scott, I'm gonna weigh in here, maybe not my place.

1st wish you were my dad when I wanted to run off on some crazy hair brained scheme, I had to learn from his mistakes, not mine, so I got to make the mistakes later in life.

If you don't want to junk up the dash with an aftermarket heat gauge that has actual temps on it, buy one of those laser pointer infra red thermometers and get the real temperature at the thermostat housing.

Blowing a head gasket at 160 degrees doesn't make sense. I tend to agree with Brian, fix the head gasket and put in a 160, but if your radiator is clogged or you have a blocked cooling package, it won't fix the problem. Rather than loosening the rad cap or getting a lower pressure one, you can drill a _small_ hole in the thermostat to let more flow through.

For the minimal cost of getting that cooling system flushed and radiator done correctly, I'd do it before going to Mexico. Not to sound xenophobic, but with the stories of young Americans disappearing, wouldn't it be best to arm your child with a vehicle that is reliable when traveling across a foreign (and yes Mexico is foreign, did it on a motorcycle and a vw bus) country.

Sorry to get off topic and rant.

Chris

He drove it about 100 miles on a test drive. Took a rock thru the windshield and blew his new head gasket. He took the Honda and should have crossed the border yesterday. Thanks - Scott

To much water flow will cause over heating! runnig without a thermostat lets the water pass thru the radiator to fast to have time to cool as a result over heating I speak from experience here.the thermostat slows the flow of coolant thru the system (when its open )and allows it time to cool as it passes thru the radiator.a 180 degree thermostat is a good starting point. if the heater doesnt get warm enough in the winter you might want to change to a 195

If running with no thermostat caused overheating then every vehicle should overheat without a thermostat and that doesn't happen. I have compared no thermosat, high flow thermostat, and standard thermostat. Engine temperature increased incrementally with each reduction in flow. It just isn't as simple as saying "the water doesn't have time to cool". I haven't heard a good explanation or analysis anywhere of why removing a thermostat can cause an engine to overheat.

Running a Stovebolt w/no stat is different than running a 98 Nissan w/o one, all car are engineered differently & have strong & weak areas. In my experience, some will run cooler, some hotter, some you can't really tell any diff. Anything w/EFI needs one tho. Brian

Hop-up books for sbc and Buick 3.8L recommend that a restrictor plate be used if a thermostat is not used. It is possible that without the restriction there is insufficient pressure to reach all potential hotspots. I do know that my 7000 RPM sbc would overheat w/o thermostat and wouldn't with one installed.