Hybrid_From_Hell Posted March 29, 2011 Share Posted March 29, 2011 OK I have always been under the impression that the cooler the thermostat fitted, the cooler the engine runs A Mate, who I know to be a clever as hell bunny, has now made me doubt this He reckons that on a V8 an 88 degree thermostat is the one to go for, and that fitting (as I was going to) a 72 Degree one will not have any effect on the overall running temp of the engine, but will just make the radiaitor work too hard, and cause heat spikes rather than a constant temp target. He says thermostats are more about warm up times in differing climates than engine target heat ranges His views (as are mine) also think heat of engine is control more By Oil Collers, Radiator sizes positioing and flows, air flow, exits from area and rad location vs usage - I agree 101% with all these ...but the Thermostat Knowing him to be as clever as a clever thing (he is) I have now started to doubt my understanding so hence this post ? He has proven me wrong many times before Discuss Quote Link to comment Share on other sites More sharing options...
nicks90 Posted March 29, 2011 Share Posted March 29, 2011 he's right - thermostat opening temp does not really affect the operating tempurature of the engine. As an example, once an engine is all up to temp and running with X radiator, Y oil cooler and Z diameter pipes with water pump etc - it might have a running temp of 93C at 70mph it doesnt matter if you fit a 72, 80 or 88C thermostat - as the thermostat will be open and have the same coolant flow through it no matter what its initial opening temp will be. However it will affect the length of time it takes to warm the engine up. Quote Link to comment Share on other sites More sharing options...
g&t Posted March 29, 2011 Share Posted March 29, 2011 this is an interesting one, can't answer it myself but look forward to the discussion - your mate's views are certainly food for thought. I have run a RRC with an 82 degree 'stat & it did (according to the gauge) run slightly cooler, at least until you hoofed it when it started to slowly overheat, but that turned out to be a rad problem. Quote Link to comment Share on other sites More sharing options...
TSD Posted March 29, 2011 Share Posted March 29, 2011 The 'stat is there to prevent the engine running too cool at light loads, not too hot at high loads. In other words, it allows you to run a massively overspec cooling system suitable for towing 3.5T through desert sand, but still get up to a proper running temperature when bimbling down to the shops. EDIT : But it should have a temperature setting within the normal running range, so it can stabilise the temperature as far as possible. (I'm deliberately not considering flow control, backpressure and cavitation to avoid starting a holy war on the subject!) Quote Link to comment Share on other sites More sharing options...
Les Henson Posted March 29, 2011 Share Posted March 29, 2011 I agree with Nick - the temp of the stat will make no difference apart from initial warm up. Water re-entering the engine after being cooled is the main factor, so rad, air flow, pipework, coolant flow speed are the main things once the engine is up to running temperature (most stats will remain open from this point on). Evidence speaks for itself - a blocked rad will make the engine overheat and cleaning it brings the temperature back down. An engine that is running too hot when the engine and coolant flow are known to be good, can only then be improved by more air flow or a better radiator. Les. Quote Link to comment Share on other sites More sharing options...
miketomcat Posted March 29, 2011 Share Posted March 29, 2011 My understanding is the thermostat opening temp is the minimum temp the engine should run at therefore if you put a low thermostat in you will run cooler only in cold weather. This as far as I know will cause increased engine wear. Your problem is firmly in getting rid of heat as I said in your other post my tomcat had to much cooling thus my thermostat would close at 70mph on a cold day! Mike Quote Link to comment Share on other sites More sharing options...
pitmole Posted March 29, 2011 Share Posted March 29, 2011 Think of things in a very simple way. Engine is a heat source producing x number of kw at max rpm Rad is a heat sink that will lose a y number of kw for a given airflow Thermostat is a balance control in the middle As long as rads y kw are bigger than engines x kw then the system will always run cool, thermostat will then control how cool. If rads y kw rating is smaller than engines x kw, ie blocked, wrong sort, other cooling prob, then it WILL overheat, whatever thermostat you have. Thermostat will stay closed until engine has reached it's temp and then allow cooling flow to start Lots of other issues as others have said, cav,flow restriction,airlocks etc, but I did say simple way! Quote Link to comment Share on other sites More sharing options...
tacr2man Posted March 29, 2011 Share Posted March 29, 2011 fitting a lower temp thermostat will make the engine run cooler , because the radiator will be capable of dumping more heat than the engine produces, in the normal run of things, otherwise the vehicle would be unusable its what happens when you overheat. the thermostat will maintain the engine operating temp , once it has reached that temp , if the heat generated is more than thru other losses , up till then the water pumps round thru the bipass system. you cant over work a radiator , it will transfer heat depending on temp differential and conductivity , in other words it will do what its design will permit and thats it. having said all the above you could be limited by requirements of fuel injection , that will run rich untill normal op temp so fitting 72 thermo may not be a good idea if the efi require 88 as the n o t. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted March 29, 2011 Share Posted March 29, 2011 I use Megasquirt to control the fans on my rangie, I run an 82c stat, fans on at 85, off at 83. If I change the temps MS switches at to say 95/92 , that has now defined the temp the engine will run at, not the stat, although it will take longer to warm up between 82 and 95. This is discounting the effects of RAM air on a cruising vehicle, which could potentially cool the engine down to stat temperature. So yes he is right, for a hard working engine, but not for cruise. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted March 29, 2011 Share Posted March 29, 2011 I agree with your mate. It doesn't matter what stat you have fitted, it will have little effect on the running temperature of the engine when it's actually being worked (i.e. stat fully open). There is some ability for controlling the temperature built in - that's the temperature range over which the stat goes from fully closed to fully open. However, this 'temperature control' would only largely be used when the engine is under low load. As soon as you start 'driving a little briskly' it's the rad/flow rate/fans etc that govern the temperature of the engine. If you really wanted good temperature control over your engine you could have a controller to adjust the speed of your fans (2 speed X-Fan?). If you were being really geeky, you could actually use the engine temperature, engine load, and road speed as inputs to a very clever controller to estimate and adjust fan speed to keep your engine at a perfect operating temperature. Quote Link to comment Share on other sites More sharing options...
forkrentfitter Posted March 29, 2011 Share Posted March 29, 2011 the size of the rad and the rad material has a large effect on the cooling,ally rads dissapate heat more effeciently than ordinary production rads,also using water wetter addative will aid cooling,as will making an air funnel in front of the rad.this has all been learn,t from running tarmac rally cars in the past. Quote Link to comment Share on other sites More sharing options...
V8 Freak Posted March 29, 2011 Share Posted March 29, 2011 As a lot have said above... The thermostat is there to initially help the engine get warm quickly. The trick is to make sure you system can "over cool" the engine when on tickover / under load in slow air and when it's travelling at speed with the normal ram effect of air hitting the front of the car.... The fans should be able to pull temperature down in static / slow moving situations, but are unlikely to be any benefit when travelling at speed. If your system can over cool, it will find a happy medium when travelling, but the thermostat will play a role... It will close somewhat and restrict flow if it starts to cool down to or even below it's operating temperature.... It's nice slow movements so no spikes. It will find a balance for the over cooled system when it's working well buy restricting the flow and opening again when it all heats up a little etc.... It's quite dynamic and you can see the changes when looking at MS logs. If I'm WOT on mine for a long period of time I do creep to 91 Celcius (93 C highest in the warmer days of the year) but it seems to settle there... Once I resume normal sublight travel, it eases back to 88 Celcius and settles around that area... Thermostat definitely playing a part in the balancing. Neil Quote Link to comment Share on other sites More sharing options...
pitmole Posted March 30, 2011 Share Posted March 30, 2011 Oh dear, there is some conflicting information here, TSD and G&T are both right in what they have said. in a correctly spec and functioning cooling system, the radiator is sized to remove all the heat the engine can produce, in it's harshest working environment, ie towing 3.5 tons at a snails pace thru the desert. The rest of the cooling system, fans, ducts, pumps, fan temp switches all help to produce the correct water/ airflow but it's down to the rad ultimately, but only if the rad is big enough for the worst amount of heat at the lowest airflow You then put in a thermostat, so that when the situation changes to -10, 70mph along the motorway, the engine is not over cooled. the value of the stat will be the running temp, thats what stats do! might be slightly different than the value written on it, but it will hold that temp. Marine engines have unlimited cooling, run one with no stat in it's heat exchanger and it will never warm up, fit a 88 stat and it will hold that exactly for days. If you have a system with a 82 stat and it runs at 85 normally but 95 when you cane it, then it is not cooling properly ie think of blocked radiators, worn pumps etc. Warm up times etc are not what the stat value is designed to do, thats down to internal waterflow and pre stat opening bleeds. Quote Link to comment Share on other sites More sharing options...
mad_pete Posted March 30, 2011 Share Posted March 30, 2011 I thought I'd try looking up Theromstat "A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The name is derived from the Greek words thermos "hot" and statos "a standing". The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature." "Perhaps the best example of purely mechanical technology in widespread use today is the internal combustion engine cooling thermostat. These are used to maintain the core temperature of the engine at its optimum operating temperature by regulating the flow of coolant to an external heat sink, usually an air cooled radiator" Quote Link to comment Share on other sites More sharing options...
landybehr Posted March 30, 2011 Share Posted March 30, 2011 My RRC runs with a 74°C Thermostat (the lowest I know of for the RoverV8. Don´t know which engine/vehicle specification was fitted with it, but it´s got a Rover-Part-Number). Now you may believe me, that the water temp gauge of the instrument cluster no longer climbs to the usual centric position. It starts moving as soon as the coolant reaches about 50°C and the point in the middle would represent what a standard RRC-3.9/4.2 runs with. So from my practical point of view, the engine runs cooler. I also see that the oil temperature is cooler too, but not by very much. I have yet not experienced the coolant gauge to go towards the middle point, even offroad. But that possibly changed at WOT on motorways (these over here quite often have no speed limit; still I never get much faster than 120km/h). Therefore I think the coolant system is well capable (under the conditions I described) enough to guarantee the lower system temperature that the thermostat commands. Quote Link to comment Share on other sites More sharing options...
Gromit Posted March 30, 2011 Share Posted March 30, 2011 Interesting read this. So is the conclusion that the temperature is controlled by the stat, in so far that it does the best it can with the heat sink available. If the heat sink is very efficient, the engine temp is absolutely controlled by the stat. In marginal situations, the overall heat sink's performance mostly determines the engine temp, which is modulated by the stat Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted March 30, 2011 Author Share Posted March 30, 2011 Erm ? Are we going around in a circle, I am getting confused ? S= Stat T= Temp A= Answers C= Are we going round in one ? Discuss some more Argue Nige Quote Link to comment Share on other sites More sharing options...
miketomcat Posted March 30, 2011 Share Posted March 30, 2011 Interesting read this. So is the conclusion that the temperature is controlled by the stat, in so far that it does the best it can with the heat sink available. If the heat sink is very efficient, the engine temp is absolutely controlled by the stat. In marginal situations, the overall heat sink's performance mostly determines the engine temp, which is modulated by the stat I think you have nailed it ^^ Nige sort your cooling then look at the stat :-b Hat coat out of here Mike Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted March 30, 2011 Share Posted March 30, 2011 My RRC runs with a 74°C Thermostat (the lowest I know of for the RoverV8. Don´t know which engine/vehicle specification was fitted with it, but it´s got a Rover-Part-Number). Now you may believe me, that the water temp gauge of the instrument cluster no longer climbs to the usual centric position. It starts moving as soon as the coolant reaches about 50°C and the point in the middle would represent what a standard RRC-3.9/4.2 runs with. So from my practical point of view, the engine runs cooler. I also see that the oil temperature is cooler too, but not by very much. I have yet not experienced the coolant gauge to go towards the middle point, even offroad. But that possibly changed at WOT on motorways (these over here quite often have no speed limit; still I never get much faster than 120km/h). Therefore I think the coolant system is well capable (under the conditions I described) enough to guarantee the lower system temperature that the thermostat commands. Agreed, but imagine running at fuill revs and full torque with no ram air cooling. Quote Link to comment Share on other sites More sharing options...
moore101 Posted March 30, 2011 Share Posted March 30, 2011 Interesting read, some very mixed views. I always thought that a thermostat will have a fully open temperature (think a 74 thermostat is fully open at 82?). Once the engine reaches normal operating temperature (88?) then the thermostat can't have anything to do with temperature or coolant flow can it because the thermostat is fully open? Unless the temperature drops below 82 at which point the thermostat will start to close. I then thought engine cooling is controlled by air flow through radiator from vehicle speed (ram effect), fans to change the flowrate of air through the radiator, or variation in waterpump speed and therefore water flowrate? Quote Link to comment Share on other sites More sharing options...
mad_pete Posted March 30, 2011 Share Posted March 30, 2011 Let's think about it like central heating. Thermostat on the wall in the hall. Unfortunately hot and cold are reversed between the cases. So house is hot in summer and you turn heating on, no need to add to that so thermostat stays off and so do radiators House is cold thermostat turns on, as do radiators until thermostat temp is reached and then it turns off and on as required to stay near that temp House is cold thermostat turns on but this time you open all the doors and windows, house stays cold thermostat stays on but house never reaches desired temp. Typically houses and cars are designed so the radiators can shift enough heat to obtain thermostat temp. So if my hall thermostat is set to 15 degress chances are my house will be colder than we it is set to 25 degrees. Seeing as the water entering the engine is colder than the water leaving it I don't see how a single temp can be applied to the whole system. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted March 30, 2011 Share Posted March 30, 2011 Let me see if I can explain how I understand it a little better. A thermostat has an opening temeperature range. It's this range that stabilises the engine temperature. For example - a 74 degree stat with the engine temperature just approaching 74 degrees at constant load (therefore constant heat into the coolant). The stat will start to open at 74 degrees pushing some hot water to the radiator and therefore returning cool water to the enigne. As the coolant heats up further, the stat will open further, until the whole system reaches a "steady state". The stat will be open far enough to allow just enough coolant to flow through the radiator to keep the engine temperature constant. This constant temperature will be above the opening temperature of the stat - say 78 degrees. Suppose the engine load increases (i.e. more heat into coolant). The engine temperature will increase from the 78 and the stat will open a little more. The flow through the radiator will increase and the whole system will reach a new "steady state", which will be at a higher temperature again. Should, however, the stat get to a temperature where it is fully open, it can be said to be "saturated". I.e. it can have no further effect on the flow rate through the radiator. From this point on, other control systems come into play - mostly fan switches, or viscous couplings to increase the heat removed from the radiator and keep the temperature within range. Depending of course on the set point of the fan switches, it might be that with no ram air cooling that your engine always remains above the fully open temperature of the stat. In this case it's your fan temperature switches that are controlling the engine temperature, not the stat (and of course on where the fan switches are located, but I don't want to open another can of worms with that one!) Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted March 31, 2011 Share Posted March 31, 2011 the size of the rad and the rad material has a large effect on the cooling,ally rads dissapate heat more effeciently than ordinary production rads,also using water wetter addative will aid cooling,as will making an air funnel in front of the rad.this has all been learn,t from running tarmac rally cars in the past. As an aside to this, when I got my custom rad made for the 109, the guys making it were absolutely adamant that it would *not* cool the engine and made me promise I wouldn't blame them. Technically I *was* doing everything wrong - brass/copper not ali, minimum number of fins-per-inch, fewer & fatter cores. If you add it all up, my rad is undoubtedly very inefficient for its size, but what it absolutely does not do is get clogged up, and if I damage it I can braze it back together. As it is, it over-cools the truck nicely. So technically what you need is a nice ali rad with a million fins, lots of narrow cores, all adds up to massive surface-area and maximum efficiency... until you throw mud at it and it clogs up if you can get your rad in the back then it's not a problem and you can go for something super-efficient and probably less than half the size of the big copper affair in the front for the same level of cooling. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted March 31, 2011 Share Posted March 31, 2011 So technically what you need is a nice ali rad with a million fins, lots of narrow cores, all adds up to massive surface-area and maximum efficiency... until you throw mud at it and it clogs up if you can get your rad in the back then it's not a problem and you can go for something super-efficient and probably less than half the size of the big copper affair in the front for the same level of cooling. I've got a BMW radiator in the front of my series - it has an enormous number of fins and is all ali construction. Despite being a little smaller (and considerably thinner) than the series radiator it replaced, it cools my 3.5 V8 nicely no matter how much I rag it. It helps that it's got an enormous fan on the back. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted March 31, 2011 Share Posted March 31, 2011 I've got a BMW radiator in the front of my series - it has an enormous number of fins and is all ali construction. Didn't I give you that one? If so, it proves the point nicely - I hauled it out of something like an old 530 in the scrappy, which pushes out more power than most RV8's, and yet the rad is as you say knocking on for half the size. Quote Link to comment Share on other sites More sharing options...
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