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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default why???

    I was pondering the design aspect of controlling the cars coolant fans from the switch in the radiator, and am wondering why is it done like this???

    I can understand why an old carby car would run this sytem.....Simplicity, but why would a modern efi car with the capabity to switch the fans from the ECU use this system??

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    Its adding another sensor/switch where there is a perfectly good one in the thermo housing.

    I have been running my fans from the ecu for a while now and cant really fault the modification.

    I am critical of the radiator sensor because when the revs are down and the temp is up, and the car is stationary it allows a spike in the coolant temp that just does not happen with an ecu controlled fan.

    WOuld anyone care to have a guess at why renault and possibly other manufacturers continued with the radiator fan switch long after efi was introduced??

    Jo
    Last edited by jo proffi; 14th December 2012 at 02:51 PM.

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    1000+ Posts robmac's Avatar
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    Although it may work very well in your case you have no aircon nor auto trans.

    Both of these can add heat load to the radiator. Having a sensor in the thermostat housing in many cars may not be best position to sense radiator temperature. For example, and I admit to no knowledge of the Fuego, if the sensor has poor coolant circulation past it you have a problem.

    Sensors in the bottom of the radiator are closed loop. IE if the radiator temperature rises the fan/s start and won't turn off until the temperature is down below the set point. Provided the sensors are in the bottom of the radiator and are immersed in coolant. No need to have a circulation happening because the sensors are immersed.

    I know you pay particular attention to heat soak and peak temperature but provided it's not causing very high temperature spot heating a small amount should not cause any issues.

    I'l be interested to hear what our resident experts on Douvrin 4s say.
    My feeling is that I would prefer to have the actual coolant temperature in radiator monitored and fans controlled based on that. Using I-O of a ECU adds a level of complexity.

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    The midwife's battle-cry remains valid, even today.


  4. #4
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    if the sensor has poor coolant circulation past it you have a problem.
    Does any car with a 6krpm redline have good coolant or oil flow at 800 rpm???

    Jo

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    Does any car with a 6krpm redline have good coolant or oil flow at 800 rpm???

    Jo
    Oil, yes, coolant depending on the pulley ratios but flow is probably minimal but so is heat generated.

    Hence the reason for fully immersing sensors at the bottom of the radiator.

    What highly modified car idles at 800 and which car runs a 1:1 water pump drive?

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    1000+ Posts PeterT's Avatar
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    Default why???

    Surely far better to have the sensor in thermostat housing? Thus a more accurate reading of the coolant temp where it counts. Mi16, 306 etc have three sensors in the thermo housing - ECU, temp gauge and fans. The latter being idiot proof. If the sensor goes open circuit, the controller turns the fans on full speed.

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    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    I know you pay particular attention to heat soak and peak temperature but provided it's not causing very high temperature spot heating a small amount should not cause any issues.
    IS it a coincidence that two catastrophic failures of the fuego have occurred at exactly the same traffic light at the top of a big hill that i fly up at wot??

    The first was a hose splitting from the pressure and spraying coolant all over the exhaust manifold, cracking it.
    the second was a timing belt sheering some teeth??

    Both items were probably due to fail anyway but I feel having the temps spike up close to boiling point would not have help the matter.

    Another aspect which I wont pretend to know much about, is the way the tune changes when the motor temp changes.
    Maybe if i had a 3 gas analyser and more IQ i'd be able to learn more but I only have an 02 sensor and modest IQ.
    I have found it easier to tune the car when the coolant temps stay fairly static.
    Most people would not be too concerned with that as this rather complex part of EFI tuning is taken care of by the factory, but I dont have such luxury and it was starting to do my head in untill I moved the air temp sensor closer to the engine and regulated the cooling temps.

    For anyone who has been following my mods and remembers stuff like an elephant, I ditched the r21 inline thermostat and went back to the bypass blocking original styled thermostat.
    The only change observed was a minor decrease in the temp spikes (at idle after high load), but less improvement than what was anticipated. The coolant was still moving too slow to trip the switch and i still needed to hit the AC switch when spikes were anticipated.
    Either that or sit at the red light reving the car up to +1400rpm and looking like a cockhead.

    Jo

  8. #8
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    I think having a sensor in the bottom of the radiator is useful in cold climates. You keep the louvres closed (or fan not engaged) until the bottom of the radiator has reached a suitable temperature where you can be confident it's not going to freeze in the breeze.

    The difference in top and bottom radiator temperature was also discussed for diagnosing cooling system problems in a diesel course I did a long time ago (Caterpillar or Cummins, not sure which). I liked the idea but have to admit I've never used it. It might be applicable when a 504 sucks the dome plug into the water pump.

    Have fun,

    Rob.

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    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    IS it a coincidence that two catastrophic failures of the fuego have occurred at exactly the same traffic light at the top of a big hill that i fly up at wot??

    The first was a hose splitting from the pressure and spraying coolant all over the exhaust manifold, cracking it.
    the second was a timing belt sheering some teeth??

    Both items were probably due to fail anyway but I feel having the temps spike up close to boiling point would not have help the matter.

    Another aspect which I wont pretend to know much about, is the way the tune changes when the motor temp changes.
    Maybe if i had a 3 gas analyser and more IQ i'd be able to learn more but I only have an 02 sensor and modest IQ.
    I have found it easier to tune the car when the coolant temps stay fairly static.
    Most people would not be too concerned with that as this rather complex part of EFI tuning is taken care of by the factory, but I dont have such luxury and it was starting to do my head in untill I moved the air temp sensor closer to the engine and regulated the cooling temps.

    For anyone who has been following my mods and remembers stuff like an elephant, I ditched the r21 inline thermostat and went back to the bypass blocking original styled thermostat.
    The only change observed was a minor decrease in the temp spikes (at idle after high load), but less improvement than what was anticipated. The coolant was still moving too slow to trip the switch and i still needed to hit the AC switch when spikes were anticipated.
    Either that or sit at the red light reving the car up to +1400rpm and looking like a cockhead.

    Jo
    Your failures sound like a lack of maintenance issue (no insult intended).

    Perhaps an electric water pump is very best option. You could do PWM (speed) control of the electric motor based on temperature via the ECU. You would to peg the low speed set point to ensure minimum flow rate.

    Maybe it's old time thinking but I would still favor having an overide temperature sensor in the radiator, even it was set slightly higher than the max expected temperature.

  10. #10
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    Your failures sound like a lack of maintenance issue (no insult intended).
    No insult, I'm sure that was the case too, but the relevent aspect was where they failed, both at the exact same spot.
    I was wearing a tuxedo in both cases too. Maybe there is a link between the chance of car failure and wearing black and white.

    Jo

  11. #11
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    No insult, I'm sure that was the case too, but the relevent aspect was where they failed, both at the exact same spot.
    I was wearing a tuxedo in both cases too. Maybe there is a link between the chance of car failure and wearing black and white.

    Jo
    Murphy's Law, sometimes referred to as "The fourth law of thermodynamics" states:

    "If anything can go wrong, it will. At the least convenient time. To the maximum detriment of the user."

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    probably the easiest thing is to not thrash the car up that hill when wearing a tuxedo.
    failing that, stroll over to the bahai temple to destress while the car cools down.

  13. #13
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    Quote Originally Posted by robs View Post
    I think having a sensor in the bottom of the radiator is useful in cold climates. You keep the louvres closed (or fan not engaged) until the bottom of the radiator has reached a suitable temperature where you can be confident it's not going to freeze in the breeze.

    The difference in top and bottom radiator temperature was also discussed for diagnosing cooling system problems in a diesel course I did a long time ago (Caterpillar or Cummins, not sure which). I liked the idea but have to admit I've never used it. It might be applicable when a 504 sucks the dome plug into the water pump.

    Have fun,

    Rob.
    This is my understanding also. Especially in trucks with expensive engines, they like to keep the coolant inlet temp at a reasonable level, not too cold - they don't want very cold coolant coming in - its like flogging the engine before it warms up, only in cold weather it would be all the time. So the temp sensor mounted in the bottom tank only switches on the fan when the coolant crossing the matrix of the radiator is not cooling enough. Its all about the difference in temp between the top and bottom tanks.

    As an aside, the most interesting system I can recall was on a large truck with radiator shutters (air operated louvres in front of the radiator. The engine did not run a normal thermostat. The sensor mounted in the bottom tank opened the shutters when it reached a certain temp, therefore allowing air to flow across the matrix. The shutters opened and closed constantly, maintaining an even temp in the system. The coolant flowed continuously at maximum flow around the system.
    Last edited by Fordman; 16th December 2012 at 01:09 AM.
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  14. #14
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    Quote Originally Posted by jo proffi View Post
    I was pondering the design aspect of controlling the cars coolant fans from the switch in the radiator, and am wondering why is it done like this???
    I can understand why an old carby car would run this sytem.....Simplicity, but why would a modern efi car with the capabity to switch the fans from the ECU use this system??
    Its adding another sensor/switch where there is a perfectly good one in the thermo housing.
    I have been running my fans from the ecu for a while now and cant really fault the modification.
    I am critical of the radiator sensor because when the revs are down and the temp is up, and the car is stationary it allows a spike in the coolant temp that just does not happen with an ecu controlled fan.

    WOuld anyone care to have a guess at why renault and possibly other manufacturers continued with the radiator fan switch long after efi was introduced??
    Jo
    Hi,
    This is not "THE Answer" just AN answer.

    Looking at the workshop manuals, most Renault cars had umpteen engines available. Even after EFI was available most O/S models probably had carbys for a long while. Or hybrid systems. So having a simple radiator mounted switch for the fan was a common part for lots of models. Simple and fits all.

    Looking at the R19 electricals you can see how the EFI wiring etc is allmost seperate from the other wiring so it can be just fitted with the EFI engine if specified. After that old habits die hard in the Auto design world.

    GM had the ECU control everything very early in the piece. THe Pulsar/Astra's even had the reversing lights ECU controlled. They had common ECUs with external individual memory chips for different models.
    jaahn

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