QUOTE(Pepperboy @ Jun 12 2021, 10:32 AM)
Ah yes, another common statement I've seen is "driving short distances often is not good for ur BMW". May I know more specifically how short-distance driving contributes to the PCV issue?
So during this lockdown period daily drive go tapau food a few kilometres away is a no-no for the engine?
Actually not limited to BMW, but any cars. Just direct injection + turbo the effect is more prominent.
This goes back to the purpose of PCV (Positive Crankcase Ventilation). Here's some history and development over time.
- the pressure of crankcase where the engine oil at is not static
- piston movement cause fast pressure change, and blow-by are adding more air to the crankcase
- The earlier engines have no ventilation and no gasket, oil leak is normal. Then gaskets were added but doesn't fix the problem. Because the pressure is pushing the oil through any gaps possible.
- The people started to make small hole at the top of the engine to release the pressure, but this is still not PCV
- This release the pressure, but the blow-by, the unburned, burned carbon etc are still containment the engine oil
- Here's the next design, connect bring a simple rubber pipe from the vent to the bottom of the car. Then open another hole to vent in fresh air, known as breather valve
- This fast moving car create low pressure (relative to the crankcase) at the bottom of the car, thus suck the air out naturally through the rubber pipe. Fresh air goes into crankcase via breather
- This is first iteration of PCV and Breather
- But the dirty air is now vented to atmosphere, the government started to mandate rules to ban this cheap but polluting solution. California is the first in the world.
- The new solution is to vent the PCV out air back into engine intake. Thus recycle the dirty air into engine to burn off. This also have other benefit of lower the combustion temperature and reduce other form of emissions.
- For NA engine intake manifold is always negative pressure, we have vacuum from the intake manifold to pull air from PCV.
- For Turbo or Supercharger, PCV need one way valve. On idle and cruising, the intake manifold is negative pressure and pull air from PCV like NA. When on boost, PCV will close.
- So now, remember the air from PCV is dirty. For port injection, the gasoline will clean the intake valve.
- For direct injection, the dirty air will contaminate the intake system, thus the famous carbon build up issue.
- Now for more expensive cars including BMW have oil air separator built into the PCV system.
- Consider this as the OEM oil catch can, with minor different is the oil is sent back to engine. Owner no need to clean the catch can.
- Japanese and Korean (not sure about the Genesis which basically designed by German engineers) usually do not have the oil air separator.
- The common of both solutions are carbon deposit will still increase over time. It is either you want to clot the PCV first or clot the valve first. Worse enough both still get clotted.
With the background, you can see yourself how short drive affect the system. The engine have less time to warm up, some case never really warm up. Short tapau most likely driving at low rpm and low load, the airflow is slow. The fresh air circulation of PCV circulation also slow, and high frequency for dirty dead air as soon as engine off (short trip = start/stop more often per same mileage). Don't worry too much as things are much better today with advance ECU to manage the timing + better engine oil the problem is less severe. One should not worry until at least 80,000KM - 100,000KM, which the remedy is known. Check the intake valves and PCV, clean/replace as needed. One should only do this 1 time for entire car ownership, maybe 2 if drive 20 years. Unless the owner drive <1KM multiple times, daily. That's an extreme case.This post has been edited by constant_weight: Jun 12 2021, 06:09 PM