The differences between the inlet and return pipes are:

1. Different locations.

Usually, the inlet pipe is above the fuel injector, while the return pipe is below.

2. Different sizes.

Generally, the inlet pipe is larger than the return pipe, and the inlet pipe is the one connected to the fuel filter.

3. Different functions.

The function of the fuel inlet pipe is to filter the fuel from the fuel tank through a gasoline filter and temporarily store it in the fuel distribution pipe on the engine. When the fuel injector is powered on, the fuel is sprayed out of the injector and mixed with air.

The function of the car oil return pipe is to allow excess oil to return to the fuel tank, reducing oil consumption.

Symptoms of blocked fuel return pipes in cars:

1. The consequences of a blocked fuel return pipe in a car are serious and can affect starting, as it is a compression ignition process. If the fuel ratio control is not good during fuel injection, it will be affected. But usually it can be started, just emitting black smoke.

2. The blockage of the car's oil return pipe is due to the abnormal oil pressure provided by the oil pump.

3. The fuel pump supplies fuel to the engine, creating a certain pressure. In addition to the normal supply of fuel to the nozzle for injection, the remaining fuel is sent back to the tank through the return line. Of course, the excess gasoline vapor collected by the carbon canister is also returned to the tank through the return line.