Shell Canada has been compensating thousands of motorists for repair costs after their fuel gauges were damaged because of an additive in the company's petrol, writes Monica Dobie. Most of the complaints have come from customers and dealerships from the Quebec and Alberta regions. The additive has resulted in a layer of sludge that forms over the sensor that reads the fuel level in the petrol tank. This causes the needles on the petrol gauge to randomly swing back and forth and also for the fuel light to indicate empty even if the tank is full.