Step by step

[lmoengnr]

The trans temp as measured by the oil temp sensor which directly contacts the fluid within the transmission, and sent via OBD system, would be more accurate and more reactive to fluid temp change.

A temperature gun would measure the temp of the sump alloy which is a big heat sink, so the sump‘s temp would lag that of the oil temp within the transmission, especially when measuring from cold.

What if the pan is steel?
If the pan is alloy, and is a heat sink, it would dissipate the heat from the fluid, and would rise in temp very closely to the fluid temp.

 

[Skylarking]

What if the pan is steel?
If the pan is alloy, and is a heat sink, it would dissipate the heat from the fluid, and would rise in temp very closely to the fluid temp.

Whether the transmission case and pan is steel or alloy doesn't matter as both metals conduct heat

The cold metal parts will conduct heat away from the hot fluid. In that sense the metal is a heat sink where the temperature of the whole mass will increase as the fluids heat energy is absorbed. The rate of temperature rise of the case/pan will greatly depend on the mass and surface area of the metal structure.

Also as the vehicle is stationary, there isnt much airflow over the transmission and little heat will be taken away by an airstream *which actually helps to increase the temp of the case and pan. Fluid temp and case temp will both continue to climb until an equilibrium is reached. The fluid temperature will increase becasue of mechanical actions within the converter and pump and such will feed heat energy into the case and pan.

The rate of heat transfer is proportional to temerature difference, surface area and thermal conductivity. How long this will take for some equilibrium to be reached between the fluid, case and air around the transmission is anyones guess.

Until some form of equilibrium is reached, case/pan temp will always lag fluid temp. How much it lags and for how long depends on the mass of the heat sink that is the case and pan. In any case, while heat flows there must be a temperature gradient within the material which means the inside of the pan will be at a higher temp than the outside of the pan. The difference again depends on surface area, conductivity, thickness, etc...

It's just basic thermodynamics which i studied over half a lifetime ago... and hardly remember any of it...

I'm sure GM has looked at these issues in great detail and probably why they state to use a scan tool to determine temperature when checking trans fluid level (it's stated within their service manual. As such i'd say an IR temp gun is just a lazy way to do it (used by service guys that probably tell you they do a full flush but simply drop the pan, change filter and refil, if your lucky).

PS:
An easy experiment in thermodynamics is turn on your gas stove and put you finder in the flame... straight away it burns, heaps... Now take a sheet of foil and put it in the flame.. it takes a while to conduct the heat so you can no longer hold it (though you'd probably need to use your other hand due to the first step)... Lastly, take a large thick and heavey piece of steel and do the same... it takes much longer before you notice the heat from the gas flame... The large thick piece of metal is a bigger heat sink than the foil

 

[lmoengnr]

Whether the transmission case and pan is steel or alloy doesn't matter as both metals conduct heat

The cold metal parts will conduct heat away from the hot fluid. In that sense the metal is a heat sink where the temperature of the whole mass will increase as the fluids heat energy is absorbed. The rate of temperature rise of the case/pan will greatly depend on the mass and surface area of the metal structure.

Also as the vehicle is stationary, there isnt much airflow over the transmission and little heat will be taken away by an airstream *which actually helps to increase the temp of the case and pan. Fluid temp and case temp will both continue to climb until an equilibrium is reached. The fluid temperature will increase becasue of mechanical actions within the converter and pump and such will feed heat energy into the case and pan.

The rate of heat transfer is proportional to temerature difference, surface area and thermal conductivity. How long this will take for some equilibrium to be reached between the fluid, case and air around the transmission is anyones guess.

Until some form of equilibrium is reached, case/pan temp will always lag fluid temp. How much it lags and for how long depends on the mass of the heat sink that is the case and pan. In any case, while heat flows there must be a temperature gradient within the material which means the inside of the pan will be at a higher temp than the outside of the pan. The difference again depends on surface area, conductivity, thickness, etc...

It's just basic thermodynamics which i studied over half a lifetime ago... and hardly remember any of it...

I'm sure GM has looked at these issues in great detail and probably why they state to use a scan tool to determine temperature when checking trans fluid level (it's stated within their service manual. As such i'd say an IR temp gun is just a lazy way to do it (used by service guys that probably tell you they do a full flush but simply drop the pan, change filter and refil, if your lucky).

PS:
An easy experiment in thermodynamics is turn on your gas stove and put you finder in the flame... straight away it burns, heaps... Now take a sheet of foil and put it in the flame.. it takes a while to conduct the heat so you can no longer hold it (though you'd probably need to use your other hand due to the first step)... Lastly, take a large thick and heavey piece of steel and do the same... it takes much longer before you notice the heat from the gas flame... The large thick piece of metal is a bigger heat sink than the foil

Don't worry, I also did 3 years of thermodynamics at RMIT.........
IR temp guns are approved tooling in Airbus and Boeing tooling manuals.

 

[Skylarking]

Don't worry, I also did 3 years of thermodynamics at RMIT.........
IR temp guns are approved tooling in Airbus and Boeing tooling manuals.

Must have been a hell of a course

Holden’s own workshop manual is quite specific that transmission fluid level must be between 30C and 50C when setting the level otherwise the fluid level will be incorrect. They state to use a scan tool (and oddly to see the trans temp in the DIC).

The accuracy of the IR temp gun or whether they are approved by Boeing or Airbus in their specific use cases is not the issue is it. The issue is whether the metal being measured is an accurate reflection of the temperature of the trans fluid. Holden makes no mention where to do a spot check using an IR gun, so if following Boeing or Airbus’ rulebook, the answer would be to not use a tool not specified in a workflow

But we’re gone off topic in the change coolant thread

 

[VFSV6FORME]

What if the pan is steel?
If the pan is alloy, and is a heat sink, it would dissipate the heat from the fluid, and would rise in temp very closely to the fluid temp.

I say 95% are steel, only the larger capacity aftermarket are alloy/heat sink type

 

[VFSV6FORME]

Must have been a hell of a course

Holden’s own workshop manual is quite specific that transmission fluid level must be between 30C and 50C when setting the level otherwise the fluid level will be incorrect. They state to use a scan tool (and oddly to see the trans temp in the DIC).

The accuracy of the IR temp gun or whether they are approved by Boeing or Airbus in their specific use cases is not the issue is it. The issue is whether the metal being measured is an accurate reflection of the temperature of the trans fluid. Holden makes no mention where to do a spot check using an IR gun, so if following Boeing or Airbus’ rulebook, the answer would be to not use a tool not specified in a workflow

But we’re gone off topic in the change coolant thread

good point,,,,,,,,, back the the orange coolant