Emergency Lights Are Not Active Shutters

Emergency Lights Are Not Active Shutters
By: Police Fleet Manager Staff

Active shutters are the latest trick to improve fuel economy on cars where gas mileage is everything. It is the difference between a mere 29 mpg and the magic 30 mpg. These cars have flaps that open and close in the lower front radiator intake opening. Electric motors open and close these lower air shutters based on engine cooling demand (coolant temperature) and vehicle road speed.

The active grille shutters are opened at lower speeds, when traveling uphill, when towing, during stop-and-go traffic in hot weather, or any other condition when the engine needs more cooling air.

The shutters are closed at higher speeds when the engine cooling demands are less. When closed, the shutters redirect airflow around the front of the car and down the sides. This makes less aero drag than allowing the air to enter the front of the car and exiting air under the car or through the wheel wells.

What do grille shutters have to do with emergency lights? The way some lights and siren speakers are mounted in front of the radiator, these devices act as grille shutters. Except, these “grille shutters” are always closed! They block incoming air all the time.

In the good old days, it was easy to get air into the radiator—grilles were as wide as the car, open above and below the bumper, and even open below the front of the radiator. No longer. In all of the newer cars, air is only let in through certain paths, and it flows out through certain paths. All the other entrances for inlet air are blocked off for better aerodynamics.

That is why opening the hood no longer helps to keep the engine cool during long periods of idling in hot weather. Opening the hood actually defeats the path the car companies have designed the air to flow through the radiators and around the engine.

Today’s police cars are very sensitive to inlet air. Even the change in the mesh design of the grille makes a measurable difference in heat gain under police operations. The upfitter’s manual or modifier’s guide usually spells this out. Beyond clear information in these manuals/guides, the car companies are understandably reluctant to emphasize just how important the inlet air is.

The facts are that every police engine is on the razor’s edge of heat management. That explains why police engines have extra or external oil coolers, or water jackets to cool transfer cases. These are not just accessories added to meet some police bid spec—they are actually needed to control heat. That also explains the increased call by some automakers for full-synthetic engine oil.

Simply put, when emergency lights and siren speakers are mounted in front of the radiator, air is blocked to the radiator. You may be able to get by with that under conditions where the “active shutters” would be closed. However, under hot conditions and hard driving when the “active shutters” would be open, the emergency lights and siren speaker continue to block the airflow.

No police department can possibly test for engine heat gain like the automakers can. So, just because the police car did not instantly overheat when the radiator airflow was blocked does not mean the blockage is not a problem. Whether the upfitters are putting the lights and speaker in front of the radiator, or the department is telling the upfitter to do so, the end result is still a compromised engine in an emergency vehicle.

Published in Police Fleet Manager, Jul/Aug 2013

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