Water Cooled Engines, Coolant Temps

Over Cooling An Engine Is An Energy Sink 

If you are in your  mid Sixties as I am, you might recall a good many conversations that spring from BS sessions in the Lunch Room, some are so memorable, you’ll carry them to your grave.

I remember we were talking about new cars at the break table, might have been the 70s?   One guy, (a salesmen type) said he had just bought a new car, and on the advice of a good mechanic friend, he tossed out the part that had caused him so much grief previously! He went on to explain that the typical coolant thermostat in a car was nothing but a restriction, it could stick; cause serious over heating and all you need to do to assure your engine runs cool, is remove it!

I thought this was a great example of a man unwilling to apply an easily learned skill.. ‘critical thinking’. Notice I didn’t say he was too stupid to do so.

  • Why is it the manufacturer of my car paid good money to put it in the car?
  • Why is it EVERY manufacturer does the same?
  • Can I find a water cooled engine where they don’t use a thermostat?

I have written about the destruction of a Chevy V8, a good year that did easily go 200,000 miles with a little care. The one I bought failed with low mileage due to the fact the thermostat had been stuck wide open for a good many miles BEFORE I had purchased it. The number one cylinder was found with so much wear ‘taper’, the rings could no longer do their job, and just a modest request for power filled the street with smoke! Yes, cylinder number one, was cooled right out of the water pump, and it was tortured most, and first to fail.

Understanding how a cooling system works is not something most of us accomplish in one bite, as there are a thousand ways to design the system, and it can degrade rapidly without the proper care.

We need reflect on those stories told to us, a very popular one is the advice to pull the stock thermostat, and replace it with a 160F, because cooler is better..

Considering the combustion process itself, we know there’s typically problems when we start a ‘cool’ engine, and some will not start at all without a pre heat. We know too cool can lead to problems from this observation alone.  

So where is the point of best efficiency? I suggest that’s a topic of another conversation, as this short post is only about running an engine too cool. If our combustion chamber is surrounded by over cooled coolant, the fuel air mix is likely to get quenched, its possible it’s ignition point will be delayed, and when the exhaust valve opens, there may be far more un burned fuel that exits with the other products of combustion. 

Stationary Engines enjoy so many advantages, we are not so concerned about weight and space, We can build coolant systems optimized for our use, but in order to accomplish that, we need define our goals carefully. Where is that point where we might use the coolant as a source of heat and NOT over cool?

We might try and answer this getting into a lot of topics, engine design, coolant types, the temperature at which the coolant can turn to a gas or steam and interfere with the ability of the coolant to maintain reasonable temperatures in and around the combustion chambers. The type of lube oil, what temperatures it can tolerate,  engine materials, and more.  Then it comes to us, this simple thermostat device can allow the engine to run in a loop at our chosen optomized temperature, AND open to transfer excess heat to our point of storage/use withotu the worry of drawing the temperature in that loop too low.  

We best apply critical thought BEFORE we design things different. The root question, why did others design it this way? 

Simple hopper systems are worth your time to study, how do these engines cool, and what is the operating temperature. Stop now, and write down your answer.

To provide a best answer, you need know the elevation, and yes, we might quickly realize that our engine is likely to be far less efficient at 7000 feet elevation for several reasons, one, we have a less dense air charge, and two, our engine will likely be running at a lower temperature and actually ‘sink’ away more of our energy in the way of steam.

How might we raise the operating temperature in a hopper system? Modify the boiling point of the coolant might be one answer, adding an anti freeze, even adding table sugar to the hopper might raise the boiling point and therefore the operating temperature.

Plenty to think about, but the thought that over cooling an engine does little more than transfer energy to the coolant, and likely causes it to run less efficiently should give you pause in designing a system that cools with uncontrolled bleed water from a pump or stream.

As I have said, Energy and Finance have a lot in common. recently Nancy Pelosi was lecturing that one of the great ways to get the US economy going is to print money and give it to the needy to spend. She only need ask herself, “If what I am preaching is really true, why not print 100 times as much?”  Of course, a next question might be, why is it we work at all, can’t we just print it and take care of all our needs?

And why do I need mention politics again? don’t I realize what a big turn off it is? My answer.. Never has there been a time when it is more important for you to do your own thinking!  Nancy Pelosi truly is one of the best examples we’ve seen in the last 50 years as to why you can not allow others to do your thinking,

Here in the State of Washington, there’s an ad on TV, a Soccer Mom makes a big pitch for why we need legalize marijuana here. There’s folks in the Media telling us all how effective this ad is, and how likely it is that we will make it legal. Soccer Moms say, we’ll tax it, and control it, take it out of the hands of the Gangs.

I remember when our State wanted to run the Loto, to entice people who can’t afford it to gamble, and then the state can spend their money.  Some useful idiots said it might be so lucrative, we’d have no other taxes at all.  Of course the way it worked out was totally predictable, the State quickly finds a use for any added revenue and is often threatening us that they are on the verge of collapse without additional sources of revenue.

 Marijuana money will quickly be used to assure more people are dependent on the State, and of course they’ll vote to remain dependent. I’d bet my Senators have wet pants thinking about adding another dependency that people can vote to keep!  Here in Washington State free lunches are offered all summer long at parks, play grounds, and even apartment buildings, not to the needy, but on a first come first serve basis, and those who are forced to fund the effort? I know a few who are on the verge of losing their houses, as they can no longer make the property tax payments, yet alone the payments.  













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12 Responses to Water Cooled Engines, Coolant Temps

  1. Jetguy says:

    “The engine does little more than transfer energy to the coolant, and likely causes it to run less efficiently”. Context is extremely important and in the entire context of the typical internal combustion engine, yes, extremely valid. Expansion and contraction are forces to deal with and the cause of the V8s failure. Running the combustion chamber and cylinder at a non-ideal temp certainly causes lots of problems.

    My challenge for thought comes from my love of studying steam engines when I was very young. I read every book I could get my hands on. I think I learned some valuable lessons, probably more important than what they were teaching in class.

    The facts are, we create a potential of high energy and then flow it to a low energy standpoint. How we do that is what determines the energy extracted from the machine. The higher the high and lower the low, the faster the energy flows. Same principal is used in steam power generation with the giant cooling towers. It also happens on steam turbine ships. You have the heat source and a cooling sink and place your engine (AKA heat pump) in the middle. There were actually steam engines that worked by cooling the steam to contract it after the expansion stroke. The atomospheric pressure is an amazing force. Ever hear of a tanker car being steam cleaned and somebody closes the cap and a rail car tanker will implode in a few seconds? They crush like a soda can in seconds.

    Point being, our engines with the crankcase open to atmosphere, fights the normal pressure with every stroke. If you remove this back pressure from both the backside of the cylinder and the exhaust system, we sudenly improve efficiency a great deal, maybe even double it. The challenge lies in the how. If the air blowing though a radiator is say 70 F then how can we get colder to create a negative pressure and no, pumping is not allowed. The only answer is to source ground water which might lie around 40-50F depending on where you are. This doesn’t work for vehicles unless you go to an evaporative setup with water spraying into the breeze flowing through the fins of the radiator. Fill her up with water and check the gas an oil? Anyway, wear, condensation and all other issues aside, if we could run less than atmospheric pressure in both the crankcase and the exhaust, then with no other changes, we might get huge horspower increases burning the same fuel. It’s far too complicated a mess for a vehicle and thus why you only find this basic idea in large stationary power plants or ships who have the advantage of the entire ocean as a heat sink. Just food for thought.

    • George B. says:

      If we choose to believe the Maritime folks, they have engines that operate at 52% thermal efficiency.. if only we could stuff it all in a Ford Focus.

      We DIYers need answer that question about heat engines.. in 1880, many if not most of the truly wealthy in America had heat engines with small fire boxes that pumped water via a sucker rod in the well to a tank mounted high. Jay Leno has one, some claim these engines were typically 1/2 hp, fuel was cheap, and the kitchen help often filled the fire box each morning, gave the flywheel a spin and pumped the tank full. WHY hasn’t anyone copied this an offered one as good now that we have CNC, laser cutting and more? Is this a potential business? screw the so called more advanced units that seem to be little more than vaporware or way too expensive. Watch my pages.. I have a heat engine I’m going to give back to the guy that sold it to me.. and tell of the reason why…

  2. bob g says:

    i write a bit on efficiency issues, both component and overall.
    because of my interest in the changfa style S195idi, and the fact it is the only engine that i have expended the effort to do a lot of serious testing, it therefore is the only engine i can base any real conclusions on… i think much of what is learned with the s195 is applicable to other similar engines in its class.

    the chinese rate this engine at 12hp continuous or 13.2hp for a one hour rating,, and it is hopper cooled as most will know. this means that at operating temperatures it will run at about 212 degree’s F under full load at sea level. this limits the engine’s output to that which the engine can provide and not build up harmful amounts of steam bubbles in and around the cylinder.

    interestingly the same engine with the hopper removed and a tstat installed can be made to operate between 205-215F (or any other region one wants to design around) however in this example the head temperature is well above that temperature reaching ~235-240F as measured on the cylinder head… the result being the engine will now output up to a bit over 15hp and be stable thermally. what this means to us is efficiency, wherein it can be easily demonstrated (and is widely accepted ) that the first kw of production is the most costly in fuel consumption, the last kw is the least costly as well as each of those under it… so the extra 1.5kw or electrical capacity the higher temperature and closed cooling system provides is given to us at a marked lower BSFC as measured in gr/kw/hr…. this alone should be an incentive to close the system, add a t/stat/antifreeze/pressure cap and a properly sized and dependable water pump.

    some of the most efficient stationary engine’s are ebullient cooled, and as such will run upwards of 265degree’s F. this is quite hot of course and not engine’s can be ebullient cooled, however most all engine’s built today can be and should be operated much closer to the higher range than that of the open hopper or worse the cold 160 degree range. that is if one is searching for optimizing efficiencies.

    to get an idea what is possible, while unpacking my notes from testing, i came across a series of testing on this system, with the s195idi… in one series of tests the engine was generating 8.1kwatts output into a resistive load bank at these elevated temperatures and was still thermally stable… however the engine had issues with failed head gskts at this level of output, something that i worked out with the aftermarket supplier that frequents our forum from the far east… once the high quality gaskets were used there was no more failures of the head gasket. the engine could be ran at this elevated ouput, run thermally stable, burning relatively cleanly with just a touch of gray smoke.. so i would expect the upper limit of the S195idi with a closed cooling sytem is around 8kwe. the fuel efficiency at this level of output is right at .100 gallons/kw/hr electrical.
    of note and to qualify the testing, this BSFC includes all parasitic loads, such as water pump, electric fan, alternator and its drive for the starter battery charging and another alternator freewheeling that is used for other testing… so the numbers are net not gross.

    so i guess if there is a question here, my answer as it relates to my experience with this engine type, would be “yes” you want to run it hot to get maximum efficiency from the engine.

    • George B. says:

      Evans coolant has solved a lot of cooling problems in race vehicles. I wonder what it could be made to do in a non pressurized looop?

      • Elden says:

        It’s been a while since I’ve been on utterpower, but stumbled across your comment. I have designed and used a system utilizing Evans coolant, no pressure and thermosiphoning. It worked well! I’m at 9000 feet altitude, and worried about traditional coolants boiling and cavitation erosion of the cylinder liner. No need to worry with a waterless system as the low vapor pressure of the water was the problem. I may be lecturing to an empty room, but there’s my 2 cents…..

        • George B. says:


          I think this stuff and similar is a good choice at higher elevations where we risk running too cool with engines not really designed for pressurized systems., no doubt some do run pressure, but your coolant choice likely removes another potential failure point. Glad to hear it worked well.

    • Quinnf says:


      Arent’ they using silicone oils now in some HP engines? Seems that, or something similar, would be a good way to get past the 100C limit without resorting to pressurizing the cooling system, which would make it much easier to run on a converted hopper cooled engine.


      • bob g says:

        i really haven’t kept up with all the different cooling strategies used by the race car crowd, i am aware of evans coolant, and the oil based coolants, but have no first hand experience with them… i suspect that there might be lifespan issues of these coolants? maybe they last long enough for the need in race engines but break down in long term use? that i don’t know.

        i run my changfa with a 10lb pressure cap, the cylinder uses 2 seal rings which is all detroit used in the series 53 and 92 engines. i figure if detroit could get by with it then the changfa ought not have an issue with it, and so far no problems with them holding the water in as they should even after a run where i forgot to start the water pump and the coolant got up over 260F (yes that was exciting) and i don’t recommend that!

        i guess to me, its just so easy to remove the tank and install a block off plate (thanks George) and from there add a small car radiator, cap, and Tstat. Adding a bosch electric auxiliary heater pump is also very easy, the little pump is very reliable, long lived, relatively inexpensive and it only draws about 40 watts or so to power it… all in all the difference in output is more than enough to cover the effort to make the changes and cover the overhead of the pump.

        while it would be interesting to try some of the alternative coolants, so far i haven’t seen the need in my application.

        • George B. says:

          The design of the engine has a lot to do with how you can cool it. (not attempting to tell you a thing Bob, but others might be interested). Hopper cooled designs, Engines with a lot of mass, seldom have areas where gas pockets can form, and create hot spots that can literally destroy an engine. Thermal siphon will work well with the 195s and similiar IF you have a radiator of decent capacity and an electric fan, OR a tank large enough to cover your run time. I love the combination of a storage tank, with a thermostatic switch and circ pump that will carry off the excess heat to a point of use WHEN the top of the tank reaches a pre set temp, the pump runs till the lower pre set is reached.

          A good number of the modern engines can not be reliably cooled using thermal siphon, as their coolant passages, and the lighter weight materials, and lack of mass require a much high flow rate of coolant to keep areas cool. I think there’s another obvious factor, in our lazy NA 195, we develop a very low horsepower figure per pound, exhaust gas temps are lower. Modern engines with turbos, produce a lot of horsepower per pound, and have a lot of heat to shed when peak power is developed. We discuss very different animals, and they require very different cooling systems.

          One big suprise for me was just how effective those old cast iron radiators are, I am talking about the ones we grew up with, where the boiler was often in the basement of the home, and the water or coolant ‘thermo siphoned’ between the radiators and the boiler. Many of us can remember a time when the sunlight was just right thru the window, and we could study the heat waves coming off these radiators, my 6/1 in the Central Mountains can run all day in temps that hit 100F, running a 1HP deep well pump and never overheat. I think it’s a rather short cast iron radiator with around 8 fins. One day I might remember to record air temperature, and see what type of load it takes to boil the water in this radiator.. I make use of used antifreeze to keep the engine block from freezing.

          As for Evans coolant, I think it’s expensive and permanent. Some Mechanics have suggested the use of Evans in Engines that have design problems and don’t cool properly for various reasons, some FORD 6.0 owners are using Evans coolant in an attempt to better mitigate cooling problems they are seeing.. Some say those high EGTs you see when loading is very high (turbos and pedal on the floor) might cause you to consider a coolant upgrade as an insurance policy, and some say engines get so hot that coking of the lube oil can occur in critical areas like supplies that cool piston skirts. It’s nice to know that none of these problems surface in our old, slow, heavy, low HP per pound stationary engines. We alos should not that an engine designed for a constant speed allows the engineer to concentrate on efficiency, a constant load engine might allow him to further optomize the power plant, and we see this type of engine in Generators, the Marine Fleet, and arguably the Rail Road.

          As a side note.. if you clicked on the Evans link.. Isn’t it hard to imagine how those inferior head bolts got made? NOT if you are buying parts from sources I study! Here is a reminder of just how important it is to change NOTHING after you certify a design. The only way you can assure you keep your head is to have your own in house lab and test samples of every critical part you buy. If you can’t do that, you are betting your future on Vendors. I will tell a quick story of a Boeing worker who was working to certify a small part, lots of them and very boring but important work.. The proceedure he was to follow (paid by the hour) was well defined. He decided he could modify that proceedure and save a little time. A Boeing QC agent caught the fact he was not following the proceedure, and he was fired. The Union had no argument as per the protection of his employment status.. period. This story helps shed light into the mysteries of Indian and Chinese manufacturer at this time. I recall a shop boy who decided cotter pins made good a quick replacements for the pins he was missing to assemble govenors. Yes.. the fly weights hung from the cotter pins, and of course the metal all too soft, and then that day came…. when the fly weight came loose and the train wreck occured. No doubt.. the shop boy might not have known about hardness, he likely thought he was most clever in helping that shipment of engines arrive to the shipping dock on time.

          Here’s more fuel for thought. It’s obvious that a shop boy can cost Ford millions! Now consider who we having running our country! You better start tilling that garden plot now.

  3. bob g says:

    i would agree with everything you said, the hp we are operating under
    vs the weight, along with the very open passages to the hot spots within the engine adds up to a pretty easily cooled unit.

    the only spot that concerns me on the 195 is the cylinder head, although it appears to be adequately cooled even at very high loading
    (i say very high only as it relates to rated power). i wonder if at max loading at cylinder head temps of 240 and above that there might be some steam bubbles formed? i don’t know for sure, however i am considering at teardown of the engine, extending a tube
    from inside the draincock (where i push the water from my coolant pump into) and form the tube so as to extend up into one of the head ports… this would take the coolant water and force it up into the cylinder head first, assuring there is no or few chances for steam pocket generation.
    it might be that the tube, could be perforated and restricted on the end so as to direct some of the water into the head, and the rest to be mixed around the cylinder via the perforations in the tube.

    there is so much that can be done to modify these engines that is so much more difficult on a more modern engine.

    as a sidebar, digressing to increasing efficiency.

    i wonder how much hp it takes to turn the oil pump, most especially when the pump pressures are set so high? i am thinking that there really is no need for more than perhaps 35PSI at full load rpm, so my suspicion is the pump pressure could be cut in half or more and in the process cut the power required to turn it.

    it would not surprise me in the least to see a full percentage point in efficiency increase for this engine by simply regulating the oil pressure and reducing the load on the engine.

    one percentage point doesn’t sound like much, but here and there it a starts to add up to real money in fuel savings, and it would stand to reason that lowering the hp requirement of the pump, ought to also impact the longevity of the little drive tang too? sure couldn’t hurt that, not that i can see.

    bob g

    • George B. says:

      I have written about this pump pressure in more than one place, it’s insane to allow pressure to reach 325 PSI, and this has been recorded with a high quality pressure gauage by a top DIYer in Texas. It take a bit of horsepower to generate that kind of pressure, and it’s so easy to regulate with the addition of a spring, ball and seat. teh big warning is.. you can lose this engine by fittign a standard pressure gauge IF you don’t assure it can handle the pressure, I’ve had pressure switch designed for 60 PSI or lower leak oil to the point where a 4 hour run would likely drain the crank case! there’s another concern here, these high pressures are also very hard on the pump, especially the pin drive. They promote failure, and this kind of failure can be real ugly. Kind of like a Ford 6.0.

      • bob g says:

        if the pressure run as high as that cold, it it likely they are still over 100psi hot, i am thinking even though the pump is relatively small, that 65psi of unneeded pressure might consume as much as 1hp to make… recovering that 1hp would be a significant boost in engine efficiency.

        with the pump turning engine speed the drag making excess oil pressure is significant.

        also makes unnecessary heat! i really can’t see any advantage to heating the oil with the oil pump!

        bob g

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