IAT and Intercooler Outlet Temperature Comparison

IAT Sensor Lies

A while ago I installed a temperature sensor in the cold side Revo throttle charge pipe where a water/methanol jet is able to attach.  This was done to compare the temperature of the charge air shortly after exiting the intercooler and once inside the intake manifold as reported by the GTI IAT sensor.

Mk7 GTI Throttle Charge Pipe Temperature Sensor
Throttle Charge Pipe Temperature Sensor

When comparing the temperature reading at each location the results were very surprising.

The chart below shows a comparison of the outside air temperature (OAT), air temperature leaving the intercooler (IC_Out), and the temperature reported by the GTI intake air temperature sensor (IAT), while operating out of boost and then into boost.

The most notable result is that the air temperature reported by the IAT sensor while at cruise is 18 degrees higher than the temperature in the throttle charge pipe.

Once entering boost the IAT sensor reports a temperature that slowly starts to approach the temperature in the charge pipe.  Even by the end of the boost event the IAT reading is 4 degrees above the temperature in the charge pipe.

IAT and Intercooler Outlet Temperature Comparison
IAT and Intercooler Outlet Temperature Comparison

Looking at the same data plotted against RPM for only the boost event it is clear that the IAT sensor is slow to report an accurate temperature.  Once the engine RPM passes 5000 the IAT closes to within 4 degrees of the charge pipe air temperature.

IAT and Intercooler Outlet Temperature Comparison
IAT and Intercooler Outlet Temperature Comparison

These results have significant implications for evaluations that rely upon the IAT sensor, common when describing intercooler performance.

One condition often reported is IAT while cruising.  As the upper chart shows, this number has no value in describing the temperature exiting the intercooler.

Another intercooler characteristic is how quickly it cools the charge air when entering boost.  As the second chart shows, this too is meaningless if being measured by the GTI IAT sensor.

Mixed Driving Air Temperatures
Mixed Driving Air Temperatures

Conclusion:

When using the reading from the GTI intake air temperature sensor there is a very small operating condition where the sensor reports accurate temperature values.

8 thoughts on “IAT Sensor Lies”

  1. Where is the sensor that collects IATs located? Is it the sensor just downstream on the charge pipe? Or is it the sensor on the manifold plenum?

        1. Yes, the IAT sensor is located within the Intake Manifold, it is co-located with the MAP sensor.

  2. Well, does that mean the factory tune is designed around an improper temp gradient?
    Implying correction of the oem sensor, may disrupt normal (expected) operation?

    Thanks for the work.
    All your data is quite a bit more granular than the normal enthusiast.

    1. My guess, the sensor reads close enough during the portion of operation when it matters most, and since it reads high any adjustments based on IAT would be more conservative than necessary, but not adverse.

  3. So I just got the Majesty V2 twincooler and I’ve yet to install it.
    (Running a Stratified ProTune in my 7R.)
    I’ve been logging IAT vs. Ambient at different speeds to collect some pre-install data, and a couple third gear WOT runs too.

    Tell me though, if you would, please, the best test(s) I can run to get an accurate IAT vs. Ambient comparison to compare stock to twincooled?

    Much appreciated 🙂 I wasn’t able to deduce exactly what to do from your post here.

    Fantastic site, much appreciate your work.

    1. Hey Will, thanks for the feedback about the site, it’s good to hear your find it useful.

      I think your third gear WOT pull will be a good condition to record. The best condition is the one you are going to be operating under where the cooling is needed. For me the third gear pull is good since it represents about the longest period of time I’d be operating at WOT before letting up and giving the IC a chance to cool.

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