Every 2CV ever built came with two often ignored but nonetheless indispensable accessories. One was the famous “cale en bois”, basically a wheel choc. In fact, the cale-en-bois is so much a part of 2Cv history that it was the official souvenir of the 2011 2CV World Meeting in Salbris, France. You are meant to use it when you have to jack up the car to change a flat tire. Sure you can prevent the car rolling away by using a brick, or a handy rock, or someone’s foot, but why would you when Citroën has provided you with these elegant devices, each lovingly carved from blocks of ash wood by French artisans for over 40 years? But the more important of the two disrespected accessories is the grill muff. Many of these simple devices can be found hiding beneath or behind a spare tire that has not seen sunlight since the Michelin Brothers still ran the company. In the early ripple bonnet days, they were pieces of water-resistant fabric that could be snapped over the grill. Later on they became molded plastic panels, that slip into slots in the border of the grill. The grill muff is an important protection for your engine, but sadly I rarely see anyone using them. The role of the grill muff is to ensure that the motor reaches and maintains its optimal operating temperature. At that temperature, the fuel and air mix correctly and burn efficiently in the cylinders. Also, the lubricating oil flows more freely and ensures proper protection for all the moving parts. Engines that chronically operate below their optimal temperatures will exhibit poor driveablity, increased fuel consumption, and accelerated wear on pistons, rings, and bearings. 2Cv engines are described as being air-cooled, meaning that they count on air rather than water to carry away the heat produced by combustion. While a more traditional water-cooled engine will have liquid coolant circulating in water jackets around the outside of the cylinders, the air-cooled 2CV engine blows air past the cylinders, which have metal fins to increase the surface area for heat exchange. But this only tells part of the story. In fact, 2CV engines can also be described as being oil-cooled. As the lubricating oil comes into contact with various engine parts like pistons and valve stems, it naturally absorbs heat. That is why your engine oil is hot if you check it after the engine has been running. The engineers at Citroën knew that oil can break down if it gets too hot. For that reason, they wisely equipped the 2CV with a small oil radiator. You may never have noticed this device since it is hidden out of sight behind the engine fan. Like any radiator, the amount of cooling that happens depends on the difference of temperature between the liquid (in this case the oil) and the air, as well as on the volume of airflow. The greater the temperature difference, and the greater the volume of airflow, the greater the cooling effect. In cold weather, the air rushing in through the front of the car is very cold. We can’t change that, except maybe by moving to Florida (which is not a bad idea….). However, we can change how much air gets in. That’s where the muff comes in. By blocking most (but not all) of the open area of the grill, the muff reduces the airflow to the oil radiator, and in fact also reduces the airflow over the cylinders. The result is that the engine reaches that optimal operating temperature we were talking about earlier. Also, the oil warms up more quickly, and therefore flows more easily, ensuring proper lubrication. All good things. Like most things, there is a right way and a wrong way to use the grill muff. You should install the grill muff when the ambient temperature is below 10C. However, to protect the engine from overheating, you must remove the muff if the ambient temperature is 15C or higher. So, how about all you 2CV owners go and dig out your grill muffs, and use them as Citroën recommends? Your engine will thank you.