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    Thread: What's the normal 09G Trans temp?

    1. n00b
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      06-28-2020 04:34 PM #1
      Hi All

      I just replaced the valve body in my 09G transmission (2007 Jetta 2.5L) My scanning tool could talk to the trans computer so i filled the trans and let the excess drain out at the correct temp to ensure it had the correct amount of trans fluid.

      I thought it would be interesting to see how hot the trans fluid gets in normal driving (normal Arizona driving in 100+ degrees) and over approx. 20 miles of in town stop and go driving the trans temp got up to 234F. I then went on the freeway and the temp went down to 217.

      I reviewed a workshop manual for the 09G trans it it says that the trans makes adjustments to the shifts at 127C/261F and reduces engine power at 150C/302F

      So the question is: - what is the normal 09G trans temp and would i expect it to be hotter in the crazy AZ heat?

      Thanks
      Gareth

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    3. Member jkmboler's Avatar
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      06-28-2020 05:41 PM #2
      Your auto tranny is cooled via the engine coolant so unless you are climbing some serious hills or towing, ambient temp should only have a minor effect, if any on the operating temp of the tranny.

      I suspect the temps you monitored are consistent with "normal" temps for the tranny.

      Anything above 260 Deg F is edging into the danger mode and the tranny control systems alter operations to protect the tranny.


      Last edited by jkmboler; 06-28-2020 at 05:45 PM.
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      06-28-2020 08:00 PM #3
      I guess you could ask for people with that type of trans to log temps and conditions at the time and see what "normal" is. That little trans cooler in the back of the engine bay should have put it up front in front for better air flow.

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    6. Member jkmboler's Avatar
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      06-28-2020 10:04 PM #4
      Quote Originally Posted by GTI's View Post
      That little trans cooler in the back of the engine bay should have put it up front in front for better air flow.
      That little trans cooler is a oil(tranny) to water(engine coolant) cooler, so placement in air flow would have little to no effect.
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      06-28-2020 10:17 PM #5
      Yes I realize that and for years trans oil cooler be it water cooling or just air have been on the front of the air flow not stuck in the back getting all the heat the engine bay has to give. Not to mention that the water style coolers have leaked and make the trans not to happy.

    8. Member jkmboler's Avatar
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      06-28-2020 11:06 PM #6
      Quote Originally Posted by GTI's View Post
      Not to mention that the water style coolers have leaked and make the trans not to happy.

      Too true.
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    9. n00b
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      06-29-2020 12:31 AM #7
      I decided to try the scan tool on my wifes V8 Genesis and ran a course of approx. 15 miles mostly in town driving with a few miles on freeway and the highest temp the trans got to was 171F. I took the Jetta on the same route and the hottest it got was 207F. The outside temp is down quite a bit to 94F (9pm and 94F, crazy AZ temps). As the Jetta uses coolant to warm the trans and the coolant is at approx 190F I assume that 207F is ok and that the higher temp earlier was due to 20+ miles of stop start in town driving in probably 108F temps. I guess that Jettas have higher trans temps than I thought.

      Is there anyone in AZ or another crazy hot state, that can see what temp there trans runs at?

      I don't know how accurate the internal trans temp sensor is, so I will try to get a temp off the trans pan tomorrow.


      Thanks
      Gareth

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      06-29-2020 08:43 AM #8
      Your car uses a bypass thermostat to route coolant to the cooler it starts to open at approximately 75 ℃ (167° F) and fully open at approximately 85 ℃ (185° F). That thermostat can be removed and check for function like you do with any other thermostat.

      FWIW some early 2.0T had 3 thermostats, one engine and two bypass..

    11. n00b
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      06-29-2020 08:33 PM #9
      So i tried my no touch laser thermometer on the trans pan.

      I took the car for a run, stopped at a couple of stores, outside temp approx. 100F. When i got home I aimed the no touch laser thermometer at the trans pan and took a few readings and looked at the scan tool to see what the computer was saying. I let the car run for 15 mins (maybe more) and the pan temp was consistently 19-20 degrees lower than the computer.

      The trans was getting cooler as it sat, running in the garage, initial computer reading straight after run was 212 and after 15 or so mins the comp said 203. The pan temp fell at the same rate (approx 19-20 degrees less than the computer).

      I checked the no touch laser thermometer against 2 other thermometers one in the house at approx 78 degrees and one in my trailer approx. 100 degrees and the laser thing was reading 2 degrees higher than the other thermometers, so i think it is fairly accurate.

      I think the internal trans temp is probably reading approx 20 degrees higher than reality.

      I'm still interested to see what temp other forum owners have.

      Gareth

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      06-29-2020 09:52 PM #10
      Quote Originally Posted by gpjlytham View Post

      I think the internal trans temp is probably reading approx 20 degrees higher than reality.



      Gareth
      What make you think it reading incorrectly? The fluid temps are going to vary depending where it is being taken, in this case VW engineers place the G93 on the valve body not on the outside of pan.

    13. Member jkmboler's Avatar
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      06-29-2020 10:03 PM #11
      Internal and external temps are not going to match simply due to heat dissipation and heat soak (specifically the lack of heat soak).

      The aluminium case of the transmission acts as a heat sink and dissipates heat (hence: lower temp on the outside of the case)

      Further, the laws of thermal dynamics make it impossible for the internal and external temperatures to be equal in an operating machine (tranny). If you could have this, you would have a perpetual energy machine.
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    14. n00b
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      06-30-2020 01:11 AM #12
      Quote Originally Posted by GTI's View Post
      What make you think it reading incorrectly? The fluid temps are going to vary depending where it is being taken, in this case VW engineers place the G93 on the valve body not on the outside of pan.
      The temp went down with the same value 19-20 degrees

    15. n00b
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      06-30-2020 01:12 AM #13
      so why did they reduce with the same 19-20 degree temp?

    16. Member jkmboler's Avatar
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      06-30-2020 01:41 AM #14
      Quote Originally Posted by gpjlytham View Post
      so why did they reduce with the same 19-20 degree temp?
      The thermal mass of the tranny case and its ability to dissipate heat is a constant. So if you were to map the internal vs external temp you would see a logarithmic delta V. In your case at the temps you were measuring, the delta V was 19-20 degrees.

      The aluminium case of the transmission acts as a heat sink and dissipates heat (hence: lower temp on the outside of the case)
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    17. n00b
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      06-30-2020 02:32 PM #15
      jkmboler, it sounds like you know your stuff but as the car was stationary and in park, their wasn't any load on the trans to generate heat and as the internals are cooled by the trans cooler, I would have anticipated that the internals cooling at a faster rate than the external pan. an example would be:- you turn on the a/c inside the car and the interior cools faster than the outside/shell of the car.

    18. Member jkmboler's Avatar
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      06-30-2020 09:09 PM #16
      Quote Originally Posted by gpjlytham View Post
      jkmboler, it sounds like you know your stuff but as the car was stationary and in park, their wasn't any load on the trans to generate heat and as the internals are cooled by the trans cooler, I would have anticipated that the internals cooling at a faster rate than the external pan. an example would be:- you turn on the a/c inside the car and the interior cools faster than the outside/shell of the car.
      Heat flows from hot to cold. The 2nd law of thermodynamics covers this - heat flows spontaneously from a hot to a cold body. So your a/c example doesn't work. Even if there was no insulation between the exterior skin of the car and the interior, if the temp outside the car is higher than the interior, the exterior skin will transfer heat into the car interior so you would never notice a cooling affect on the exterior skin of the car no matter how long the car ran the a/c.

      Don't be fooled into thinking an automatic tranny doesn't generate heat just sitting in park. The torque converter in a auto tranny is spinning and generating significant heat just sitting in park. Also, the tranny cooler is sitting at 190 Deg F (engine coolant temp) when the car is at operating temp.
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    19. n00b
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      06-30-2020 09:18 PM #17
      Even if there was no insulation between the exterior skin of the car and the interior, if the temp outside the car is higher than the interior, the exterior skin will transfer heat into the car interior so you would never notice a cooling affect on the exterior skin of the car no matter how long the car ran the a/c

      if i'm outside in 100 degree heat and i fill a glass with ice and pour water on the ice, the outside of the glass quickly cools (no insulation). i assume the same effect happens with a car?

    20. Member jkmboler's Avatar
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      06-30-2020 11:57 PM #18
      With your glass of ice water example, the surface of the glass will remain cooler than the ambient air temperature for a short period of time. The ice will melt and the water temp will rise until the water temp equals the ambient temp. The thermal mass of the ice water is initially able to overcome the ambient heat and keep the glass surface cool, but this will be short lived. Put a fan in front of the glass and blow that 100 Deg air across the glass and it will melt and warm up much faster.

      With a car, your a/c will maybe get the interior temp to 60-65 Deg. But the car a/c has very little thermal capacity and if the car is in the sun this will further exasperate the thermal loading and your ambient temp of 100 Deg will rise to 150+ Deg on the surface of the car and the interior temp will quickly begin to rise, the surface of the car will be hot to the touch the entire time.

      This is why your a/c works very poorly sitting in traffic or at a standstill. When the vehicle is in motion air moving across the condenser improves the a/c efficiency and the very act of air moving across the vehicle in general cases cooling (wind chill).

      If you have a kiddy pool filled with 60 Deg water, sitting in the sun on a 100 Deg day, the pool will fairly quickly rise in temp, eventually equalising with the outside air temp.

      If you have an Olympic pool filled with 60 Deg water, sitting in the sun on a 100 Deg day, the pool will slowly rise in temp, and in a much longer time period equalise with the outside air temp.


      This is thermal mass.



      If you take that same car and fill it with ice, right to the top and add water, same as the glass, the surface of the car will feel cool, until the ice melts and the water warms just like the glass. The ice/water has significant thermal mass compared to the car a/c.


      I think we are getting a little off topic. I suggest you sign up for a college level class on Thermal Dynamics. Usually two terms, spread across two years.
      Last edited by jkmboler; 07-01-2020 at 11:11 PM.
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    21. n00b
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      07-01-2020 09:55 PM #19
      off topic but interesting

    22. Yesterday 09:11 PM #20
      Every 09G transmission I ever checked was running over 220 degrees, which is WAY over spec.
      According to Aisin, the Japanese transmission maker, the transmission should be more like 90 degrees only.
      So my advice is to run your own external cooler and disconnect the coolant lines from the engine, that are WAY TOO HOT!

      Every time I do this, each car I do it to shifts MUCH better, and lasts longer.

      By the way, you can also break off the red cap on the factory ATF filler and add a 2' length of 1" acrylic tubing, so you don't have to fill from underneath.


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      Yesterday 09:42 PM #21
      Quote Originally Posted by kirk_augustin View Post
      Every 09G transmission I ever checked was running over 220 degrees, which is WAY over spec.
      According to Aisin, the Japanese transmission maker, the transmission should be more like 90 degrees only.
      So my advice is to run your own external cooler and disconnect the coolant lines from the engine, that are WAY TOO HOT!

      Every time I do this, each car I do it to shifts MUCH better, and lasts longer.

      By the way, you can also break off the red cap on the factory ATF filler and add a 2' length of 1" acrylic tubing, so you don't have to fill from underneath.

      I take it that 90° is referring to C & not F so under 200°F which is in the range that I have seen for trans life of between 175-200°F

      FWIW that filler location will not be on most MK5

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