Crankcase vent valve frozen? These 5 tips will help you avoid costly repairs in the long run!

Crankcase vent valve frozen? These 5 tips will help you avoid costly repairs in the long run!

Got crankcase vent valve frozen? These 5 tips will help avoid costly repairs that these problems can cause!


The crankcase system is the ventilation system for your vehicle’s engine that houses the pistons, rods, and all of the components that transmit power into the crankshaft. Typically, the crankcase is used to store oil, while any space that is not taken by oil is occupied by air. The movement and heat made by the crankshaft rotation creates a positive pressure in the crankcase. During engine operation, gases that escape past the piston rings into the crankcase, or “blow-by” gases, as well as oil mist from the rotating components of the engine, build a positive air pressure in the system. The crankcase ventilation system needs to alleviate the air pressure from all of the moving components in the crankcase, but do so in a way that is clean for the environment.



Manufacturers are trying harder than ever to regulate unburned hydrocarbons with built-in emission systems. Hydrocarbons come from two main sources on the modern automobile: one from fuel evaporation, and the other from crankcase vapors. Crankcase vapors were long ago vented to atmosphere; however, due to tighter emission regulations, now have to be reburned as part of the combustion process. They do this through the PCV valve and oil separator.



The positive crankcase ventilation valve, or PCV valve’s main task is to take the vapors produced in the crankcase (where the crankshaft and motor oil reside) during normal operation and redirect those vapors into the intake system to be burned. While it would be simple to route a hose directly to the intake system to reburn these vapors, it’s not exactly a good idea. The valve’s job is to carefully monitor the amount of vapor entering the intake, as this can dilute the air/fuel ratio (AFR) to undesirable amounts if left unregulated. When the car is idling, AFR is critical in preventing small amounts of vapors from re-entering the system. At higher speeds, more vapors are allowed into the intake system.



One way this valve can fail is by sticking open, or having a torn diaphragm. When one of these happens, it allows more air than the vehicle’s computer has calculated into the system. This causes a lean condition, excess burning of oil, fouling of spark plugs, and a rough run. Faults such as P0170 and P0173 will show up in the engine’s computer, while smoking from burning oil can also occur.


While the valve sticking open will cause a problem, the valve being stuck closed will leave you with a similar outcome. This usually happens due to cold weather causing the valve to freeze shut . As most know, with anything that heats up and cools back down, condensation can occur. This condensation of moisture is usually due to many short trips without proper heating of the engine. On many late model European vehicles, the crankcase vent valve, oil separator, or cyclone separator will build up with moisture mixed with oil vapors and will make a creamy yellow sludge that can freeze the valve shut. This butter looking condensation can freeze, blocking the system. Without proper air venting, oil can shoot into the cylinders or out of gaskets, hydrolocking and seriously damaging the engine. This is especially problematic on BMW, Volvo, Audi, and Volkswagen vehicles.


Having seen this problem on hundreds of vehicles, I started to wonder why some vehicles would suffer worse than others. Talking with customers, I started to see a pattern in driving styles that could contribute to the problem. If you start to notice this yellow, milky build-up, here are some ways of preventing it and maybe even clearing it up.
-A good and obvious way to get the excess moisture out in the oil is by performing an oil change at the beginning of the cold-weather season.
-Let your vehicle warm up to operation temperature (roughly middle coolant temp mark) or for 20 min before you drive, and if possible let idle for up to 5 min once you arrive.
-Long drives over 45 min allow moisture to vaporize properly and make it through the crankcase system into the intake system for burning.
-A few times during a drive, do a few full short full throttle runs. This rapid change of pressure can quickly pull moisture into the engine. and burn it. Of course, keep it under the speed limit!
-If you are good at remembering, leave your oil cap and dipstick removed and open overnight. Once you come back from a drive where the vehicle got nice and hot, just remove the cap and dipstick and put to the side safely. This will allow any moisture to evaporate naturally. Just don’t forget to put them back on, as this can cause a huge mess! I suggest leaving your hood open if possible, so you don’t forget.



Here is the crankcase ventilation system found on BMW Inline 6’s from 1999-2006.
Part numbers are as follows:
1161 7533 399 Oil Separator Hose
1161 7504 536 Breather Hose
1161 7533 398 Breather Hose
1161 7533 400 Crankcase Vent Valve



Ultimately, the only sure fire solution is to replace the crankcase vent valve, and then follow these tips to keep buildup from occurring. If more peace of mind is needed, some manufacturers have switched to a heated crankcase valve which can further alleviate the issue. It runs an insulated blanket with an electric warmer circuit. Manufactures such as BMW use this set-up in climates that are even more extreme than the Chicago area, which might be hard to believe considering the record lows that Plainfield and Naperville saw a short time ago. If you are seeing signs of crankcase build-up or any other issues you might think are related to something in this article, feel free to give us call with any questions you might have.


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