Oil catch can full#

So, basically a catch can ensures the air which is vented from the crankcase is clean before it is fed back into the engine’s air intake. Here’s a dirty EGC (exhaust gas recirculation) valve in the Flashlube workshop, showing the sort of gunk that a…catch can can catch! It works in two ways by gravity, relying on the fact that oil is heavier than air to separate the two, and more importantly by a filter. That’s because it’s literally a can that catches, and what it catches is oil. This is where an oil/air seperator comes in, otherwise known as a catch can. That was pretty bad news for emissions, so a new solution was needed. The road draft tube basically emitted to the outside air crankshaft gases, a noxious mix of air that had been in the crankcase, unburned fuel, and burnt gas from the cylinders.

But there was a bigger problem – pollution. It relies on significant vehicle speed to operate effectively, otherwise the suction effect would not be created, and it was a way for water to enter the crankcase too. To equalise, another vent brought in fresh air. As speed increases, the vehicle’s slipstream creates a low pressure area around the end of the pipe which sucked air from the crankcase. The easy solution is to vent the crankcase to the outside air with a small pipe out in the vehicle’s exterior airflow called a road draft tube. Blow-by tends to get worse with an engine’s age. Ideally, that gas cannot escape past the piston seals down into the crankcase, but nothing is perfect so inevitably some gas manages to get past – this is called ‘blow by’, as it “blows by” the piston seals into the crankcase. This gas needs to be expelled as its not helping with lubrication, and with lots of gas in the crankcase you get a positive crankcase pressure, which means its harder for the piston to move up and down. When the pistons go up and down as part of the normal four-stroke cycle a lot of gas pressure is created.

Oil catch can full#

A byproduct of this process means the air in the crankcase is full of oil. The actual lubrication is done via a fairly complex design of small holes through which oil is pumped, creating a thin film of oil. Like any moving metal parts, crankshafts require lubrication, and that’s done by drawing oil from a storage area called the sump. There’s also the crankshaft, and connecting rods (conrods) to link the pistons to the crankshaft.

This is the part of the engine block that houses the pistons, which go up and down within the block.