Background:
While doing some work with an aftermarket intake manifold I noticed that the product could be opened up by removing several bolts that join the two halves.
This gave me an opportunity to inspect the position of the IAT sensor inside the intake manifold. I’m curious about this position to see if it helps explain the variation in intake air temperature with changing airflow.
Observations:
With the intake manifold opened I mounted a MAP sensor to the manifold.
Right away it looked like there might be an issue with the position of the IAT sensor when the MAP is installed on this intake manifold.
My concern is that with the sensor close to the wall of the intake manifold there may not be much air flowing past the sensor, and the body of the intake manifold might be heating the sensor.
With a stock intake manifold available I tried to make a comparison.
Step one was to measure the depth of the hole that the sensor fits inside.
Approximately 9.5 mm deep.
I estimate that the housing of the stock intake manifold is at least 1 mm thick. So the shrouding of the IAT sensor takes place down to 10.5 mm along the sensor body.
In comparison with the aftermarket intake manifold, it looks like there are a couple of additional millimeters of clearance between the intake manifold body and the IAT sensor tip with the stock GTI intake manifold.
I believe this is a good thing to have, to keep the sensor tip away from the manifold wall.
Conclusions:
My opinion is that the stock GTI intake air temperature sensor is not positioned well to measure the air temperature inside of the intake manifold.
The aftermarket intake manifold that was evaluated in this post raises the IAT sensor tip slightly, which may degrade the accuracy of the measurements of intake air temperature.
The aftermarket intake manifold being evaluated is a prototype and may not be representative of other products. A quick search for other intake manifolds for the Mk7 produced a result from German supplier Bar-Tek, which appears to have a similar mount for the MAP sensor.
I wonder if it would be possible to test getting the MAP sensor further inside the manifold air stream to see if that improves its accuracy. If the stock sensor is poorly positioned, and this aftermarket location is worse, then would the opposite be better?
I was thinking about how that might be possible, but so far haven’t thought of a way to move the sensor. One idea is to mount the stock IM on the bench and then use a different temperature probe to check different locations while trying to heat the IM. While that might confirm the theory, I don’t know what use the information would be since I have no way to reposition the MAP sensor.