Test Results Fog Light Removal


Installing the Canadian Grills to get more air flowing to my cars Intercoolers (ICs) always was in the back of my mind as a relatively low cost way to improve the cooling of the ICs and hopefully gain a little more performance out of the car. I had discussed with an Audi tech my contemplation of an Intercooler Misting kit and they had suggested that one of the best bang-for-the-buck ways to cool the ICs was with the Canadian Grills.


With that endorsement, I began down the path of installing them. I contacted my dealership and asked about the costs to get the grills and have them painted. Total cost would run about $180. That was more than I was comfortable spending on a mod that had yet to really prove itself, so I considered some alternatives.

Options Available:

  • Canadian Grills.
  • Remove foglights and leave empty holes.
  • Find something to cover the hole that would allow air to pass.


I decided to visit Home Depot and look for something that I could use to cover the foglight holes that would still allow air to pass. I happened upon this plastic ventilation cover that seemed like it would do the trick. Cost $1.90 with tax.


I had made some data logs prior to doing this mod, but the comparisons I could make were of data collected on different days. The initial results did not show much of an improvement, if any. So I decided to do a better test.

With the grills covering the foglight holes I took the car out on a hot afternoon to warm the car up. After allowing the coolant and oil temps to climb and stabilize I headed home with ten miles behind me. I brought the car home and let it sit for 15 minutes to allow the ICs to heat up.

I then hooked up my Vag and started datalogging as soon as I began driving. I had established a route to drive that would allow me to compare closely before and after performance. The first half of the route allowed me to maintain a constant slow speed of 25 mph. Then I entered a 55 mph highway where I could let the ICs reach a steady state temperature.

Finally I returned home at 25 mph. I pulled the grills off, replaced the foglights, and put the grills back into place. It was now 20 minutes later. I hooked the Vag back up and made a second datalogging run over the same course. This run was identical to the first except for getting caught at a stoplight late on the highway run for a couple of seconds.

The graph below shows the results of these runs. On the first run the cars temperature readout showed 90-91 degrees F throughout. On the second run it was reading 89 degrees F.


I had hypothesized that at lower speeds the absence of the foglights would allow the ICs to cool more rapidly, but the results of my test did not show that to be the case. I would have thought that they would have reached steady state temperature quicker at highway speeds also, but again that did not turn out to be the results I got on this test.

The only significant difference I can see between the two runs was an indicated outside air temperature 1-2 degrees lower without the foglights. But this is suspect since the car’s temperature gauge is not particularly accurate and the two runs were made 20 minutes apart.

Based upon the results of this test I have decided to leave my foglights in.

Here’s a good post to help explain these results. Graph and explanation provided by Makarov.

I found some interesting cooling performance test results here at work that actually help clarify why audi put the fog lamps in a place which might seem to block cooling to the intercoolers. the results show that the plan-view curvature of the fascia forces air around the vehicle in such a way that at some point, no air will flow into the openings; it will instead flow tangent along the surface. That point is dictated by many variables, mainly the curvature of the fascia, but also the velocity of the flow and the shape immediately surrounding the opening (the presence of air guides, for example). in the case of the car tested here, there was not really any cooling gained by opening up the outer most area (similar to the S4 foglamp area).

Audi B5 S4 Information and Testing