Originally Posted by gearmesh, inc.
No offense taken at all, Rob. None of us ever really stop learning something as long as we wake up with a heartbeat and see the sun every morning.
As far as the transmission industry as a whole is concerned, I don't think the engineers can even come up with an "official" place to take a temp reading. Of course, when these engineers are doing their simulated 100k mile R&D testing, they have multiple temp gauges just about everywhere. From this, they know for sure what external coolers in oem applications can do, but only at stock horsepower levels. We as hot rodders end up doing our own engineering beyond that in order to keep our machines alive at elevated horsepower levels.
Most people that take up the task of installing a temp gauge on their transmission usually only intend on one gauge with one sample point. Personally, in my own opinion, I tend to favor the pan for a sample point. Sure, you won't be able to see how much heat your converter puts in the fluid when stalled up, but the pan will be more of an average reading across all operating conditions. All electronic operated transmissions that I know of that have temp sensors have the sensor somewhere on the valve body, which is submerged down in the pan. I don't know if this is the intended strategy of theirs, or just simply a low cost mass produced way of doing things.
When you are cruising down the interstate in lockup, the cooler out line is pretty much the same temp as what is in the pan. During lockup in overdrive, the biggest heat maker is the planetary that is making the overdrive ratio. The fluid that passes through the planetary to lube it just drains back to the pan. When out of lockup during city driving and racing at the track, the biggest heat maker is the converter due to the fluid shear inside of it while the converter is unlocked and multiplying torque. This fluid gets cooled down in the cooler before returning back to the lube circuits of the trans.
For those of you that have high stall converters and bracket race, you may prefer to monitor your temps on the cooler out line. Consistency can suffer when you are already staged and stalled up for an extended period while waiting for the bonehead in the other lane to finally learn how to stage his car. The hotter the fluid gets, the thinner its viscosity, resulting in a "looser" converter when at high temperature.
As for the temp in the return cooler line, this temp will be just a tad cooler than what is in your pan. The pan gets to see the temperature rise from planetary use in overdrive. If you don't have an overdrive trans, the cooler return temp will be pretty much what your pan temp is.
The location you take a temp just boils down to personal preference. Do you want to see the hottest your fluid ever gets in the converter, or are you satisfied with an average reading in the pan? Or how efficient your cooler is? The choice is yours. Ease of installation is also a consideration, as some hot rodders don't feel comfortable with striking an arc to weld a bung in their pan.
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