If because there is the obvious risk of it becoming a fire hazard, something which could keep short-term insurance underwriters awake at night, the use of smoke to test for vacuum leaks could be regarded as being controversial. But if DIY practitioners or self-taught motor mechanics have taken time and effort to study and practice the smoke test vacuum leak application as it should be carried out, then all should be well, going forward.
Already, the motor engine is sucking in air that is mixed with fuel. It is then compressed and ignited in order to propel the power required. And while in motion, the engine is force to draw air through a partially closed butterfly valve. This valve creates the vacuum. An emissions control system needs to rely on negative pressure in order to prevent fumes from escaping. With the onset of emission control systems in much earlier years, numerous vacuum lines existed within a single engine.
And within these, there was always the possibility of a vacuum leak. In recent years, those vacuum lines have been reduced. And yet they still exist. And in response, the Environmental Protection Agency insisted that leaking gas fumes had to be reduced to a big fat zero. Currently, the EVAP system on every new car on the road is still controlled by an engine vacuum. By the time the car’s engine is switched off, its system will have captured fuel vapor.
The vapor gets transferred back into a running engine as well as a network of vacuum hoses. When leaking occurs, a decrease in fuel economy arises. All across the engine board, exhaustion occurs. And to think that, much earlier, it was suggested that the smoke test vacuum leak would be controversial.