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  1. Join Date
    Dec 2007
    You got it only half right, it has 2 functions.

    1. To bring the engine up to optimum operating temperature as quickly as possible; and
    2. To maintain the engine at optimum operating temperature thereafter.

    The first.

    To ensure that the engine reaches optimum operating temperature as quickly as possible, the thermostat restricts the flow of water from the engine to the radiator to virtually zero (a small flow is required so that the thermostat experiences changes to the water temperature as the engine warms up) until the engine reaches optimum temperature. The thermostat then opens up to allow coolant to flow through the radiator to prevent the temperature rising higher.

    This mod only slows this process 10F to 20F will have almost no measurable effect on AF/Ratios when dealing with hot climates. If your car is running 20F over the stock T-stat your loosing power and increasing detonation in the motor.

    The second part of what a T-stat does.

    With the engine at optimum temperature, the thermostat controls the flow of coolant to the radiator so that the engine is maintained at optimum operating temperature, even as the power output, and therefore heat output, of the engine vary with varying load conditions.

    Under peak load conditions, such as labouring slowly up a steep hill whilst heavily laden on a hot day, the thermostat will be approaching fully open because the engine will be producing maximum power, the velocity of air flow across the radiator is low, and the temperature differential between the radiator and the cooling air will be low. (The velocity of air flow across the radiator and the temperature difference between the radiator and the cooling air have a major effect on its ability to dissipate heat.) Note that even with the engine operating at full power, the thermostat should not be fully open, That's why you don't remove it from the vehicle.

    Conversely, when cruising fast downhill on a motorway on a cold night on a light throttle, the thermostat will be nearly closed, because the engine is producing little power and the radiator is able to dissipate much more heat than the engine is producing. Allowing too much flow of coolant to the radiator would result in the engine being over cooled and operating at lower than optimum temperature. Again this is why you should not remove it.

    The thermostat is therefore constantly moving throughout its range, increasing or decreasing flow of engine coolant to the radiator, in response to changes in power output due to vehicle operating load, speed, and external temperature, keeping the engine at its optimum operating temperature.

    Do all vehicles need this, no. But if your running past 195F/90C especially sitting in traffic when there is little cool air flow over the radiator. (fans don't cool much with hot air flowing over them) Or if you have a heavy vehicle with a under-powered motor or hauling a heavy load. It can make a noticeable difference in engine performance especially getting rid of detonation in the engine which further kills power and increases exhaust gas temps.

    As you have actually proved the point of this mod with your temp numbers.

    On my Civic, with the halp of a ScanGauge, it shows that this temperature is between approx. 90-100C. I've observed that the radiator fans starts turning at 101C and stops at 94C. With the A/C on, the temp can go as low as 92C

    Read more:
    Your hitting 101C/213F and your only cooling down to 92C/197F Your vehicle has a 195F/95C stat in it the most common OEM stat.

    The optimum T-stat temp for tropical and desert temps is 82C to 85C.

  2. Join Date
    Jan 2009
    So if we follow your logic, in a dessert or hot climate, your engine should operate at roughly 85C, but in the cold, it should operate at 95C? That shouldn't be the case, right? Your engine should operate at or near 95C regardless of the local climate. That's the point of having a thermostat in the first place.

    As per my thermostat specs, it starts to open at 80-84C and it is fully open at 95C.

    Here's some good reading from: Will installing a lower temperature thermostat... — Yahoo! Autos

    Will installing a lower temperature thermostat help my engine run cooler and prevent it from overheating?

    Yes, but it may cause more problems than it cures if you have a late model vehicle. Before emission controls and computerized engine controls came along, it was a common practice to install a cooler (160 to 180 degree F.) thermostat for summer driving. The lower thermostat lowered the engine's operating temperature, which in turn reduced the load on the cooling system and reduced the danger of overheating during hot weather driving or when towing a trailer.

    It was also common practice to again replace the thermostat come fall and install one with a higher (190 to 195 degrees F.) temperature rating. This would raise the engine's operating temperature so the heater would put out more warm air on a cold winter morning.

    This practice is no longer recommended because today's computerized engine control systems require a constant year-round operating temperature of about 195 degrees F.. The engine's emission controls as well as it's fuel and spark control systems are all calibrated to work within a given temperature range. If someone replaced the thermostat with the wrong one for the application (either colder or hotter), it can cause driveability, fuel economy, performance and emissions problems. So if the thermostat is replaced for any reason, it must be replaced with one that has the same (or correct) temperature rating for your vehicle.
    How Temperature Affects Engine Operation

    How Temperature Affects Engine Operation
    Coolant temperature is used for a variety of engine and emission control functions. The coolant sensor on late model engines tells the computer when the engine has reached normal operating temperature. This, in turn, affects fuel enrichment, spark timing, operation of the EGR valve, purging of the charcoal canister, etc. Even on many non-computer engines, thermal vacuum switches (TVS) that react to a specific coolant temperature are used to open and close various vacuum circuits that regulate fuel enrichment, timing and emissions.

    If a colder thermostat is installed, the coolant may never get hot enough to trigger the appropriate control functions in the computer or TVS vacuum circuits. As a result the engine will run as if it were continually cold, which increases both fuel consumption and emissions. Too low an operating temperature also increases cylinder wear.

    CAUTION: Under no circumstances should an engine be driven without a thermostat! This can produce thermal stress that may crack a head or block!

    What about a hotter thermostat? A hotter than normal thermostat in a late model computer controlled engine may activate some control functions too quickly or out of sequence with other control devices (timer delays, etc.) --which could also have an adverse effect on driveability, fuel economy, performance and emissions.
    I hope you don't take this as arguing. I still believe that stock is best for engine longevity, as it was designed. Messing around with the engine cooling balance is generally not a good thing, unless you have substantial scientific evidence to say that "this" or "that idea is better".

  3. Join Date
    Dec 2007
    It's good to have a lively discussion. But post like the one you quoted are from basic mechanics or some engineer guy how thinks in theory not facts. People who actually tune and modify cars know that the opposite is true.

    10 degrees in temp is not going to significantly change your air fuel ratio it plays zero role in keeping a fuel injected computer controlled car in open loop vs closed loop operation.. There's a reason why high performance cars have the lower stats and why lower temp stats are available by companies like hypertech and many others. There is a lower temp T-stat available for just about every performance car on the market and there has been for at least 20 years, I think 30 years of tunning makes the above argument a null and void point.

    When I say theory vs fact it's the fact they have never scanned the vehicle to check the differences in AF/RATIO, knock count, 02 sensor reading, exhaust gas temp, engine coolant temp and engine block temps to prove the basis of their theory.

    That's the difference between a tuner and a basic mechanic or a engineer who knows how something is supposed to work but does not know all the variables that can make it work better. Also the difference between the two is we know that the cars ECM is designed to adjust itself to changes and keep the AF ratio as close to what it is set at. Again changing the STAT will not significantly alter your AF Ratio. Also these guys have no concept of engine detonation all it's ill effects, especially on fuel economy, increased emissions, increased combustion temperatures, all which physically not theoretically cause engine wear.

    So the bottom line is running a 180F stat or drilled stat will NOT keep your engine in "warm up mode" aka open loop, nor will it cause the ECM to alter the fuel map and use more fuel. What it will do is keep knock down, reduce under hood temps and also allow for more ignition advance. Every degree of knock is about 3 wheel horsepower lost. It will also not throw a engine code something it would do if the engine was out of normal operation.

    Operating temp depends on the cooling system, mainly the radiator, and the flow from the pump, it's only going to take out so much with X amount of flow and that's relative to the valve sizing of the stat and how far it moves per degree and the ambient temperature.

    Dropping a 180 T-stat into your ride or doing the drill modification isn't really going to hurt it in any way, the temperature rating is for the opening not operating. Operating temp depends on the cooling system, mainly the radiator, and the flow from the pump, it's only going to take out so much with X amount of flow and that's relative to the valve sizing of the stat and how far it moves per degree and the ambient temperature.

    It's a closed system, it's going to balance at some point and stay there.

    Hopefully this is a little clearer in my early morning rant

  4. Join Date
    Jan 2009
    Wow. That's one lengthy reply. You seem to know your stuff... not quite my comfort zone doing that to my perfectly-working engine. But, good luck Anyway, let me just add that if people take care of their cooling system, it will take care of them and changing/modding the thermostat will be kinda moot.

  5. Join Date
    Dec 2007
    You are correct most cars will never need this done, but there are plenty that are in vehicles never designed for use in the Philippines climate or just have a poorly designed inefficient coolant systems, vehicles that are under-powered for prolonged use especially if under a heavy load, or engines that are modded to run higher boost this is a good mod for you.

  6. Join Date
    Mar 2008
    Greek... Greek..
    knowing a lot is one thing... enabling us to understand it, is another..
    AF/RATIO... STAT... T-stat...
    and then we use Centigrade here, not Fahrenheit..
    9/5 C + 32 = F ..
    we never had this problem at all when we were into beetles and kombis..

  7. Join Date
    May 2009
    ^no water, no problem. the great vw.....

  8. Join Date
    Jul 2003
    I really wanted to know how or what is the definition of performance mod.
    How does it affect all the other variables such as efficiency and greenhouse gas emission?

  9. Join Date
    Jan 2011
    whatever people are saying, i still rely on experience. i have passenger jeeps with bigger diesel engines. these jeeps are running all day long in hot environment. with the t-stat on the engine, the coolant flow to/from the engine is restricted by it. the idea of removing it is to have the coolant from the engine pass thru the radiator on a faster rate. mas mabilis ang cycle pag walang t-stat. gas cars are different, they really need t-stat. afaik, walang pampasadang dyep na may t-stat. dahil pag may t-stat yan, tirik sigurado. some jeep owners removed the front grills para walang restriction sa hangin papasok sa engine bay.

  10. Join Date
    Jun 2006

    Diesel engines of jeeps are purely mechanical... There are no electronic gizmos to speak of that will monitor this and that and that and this...

    Modern gasoline and yes, diesel engines are now governed by the ECU... They monitor everything to provide the best fuel economy given the driving condition/s...

    That's the reason for the presence of thermostats in present day engines; to provide a constant temperature in order for the ECU to provide the best settings for best fuel economy...

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Should you remover thermostat?