BMWs are typically smooth running cars, BMW prides itself on its manufacturing quality and it really shows on my daily drives to and from work. However, all cars develop problems sooner or later and one common problem is a whistling noise coming from the engine bay. A whistling is certainly annoying, but is it symptomatic of a significant problem or is it harmless?
A BMW whistling noise could have several causes. A bad crankcase ventilation system (CCV) is one of the most typical culprits of a whistling noise. Other common causes include a cracked valve cover, bad crankcase breather hose, or a bad vacuum line. Diagnosis is relatively simple and repair is usually within the scope of a DIYer.
These are the most common causes of a BMW whistling noise, but let’s take a closer look at how we can diagnose this issue. Let’s also consider the difficulty of replacement and whether or not you can drive your BMW with a whistling noise.
How to diagnose that whistling noise
Typically when someone hears a “whistling” noise in their car it is usually coming from the engine bay area. Whistling noises are almost always caused by a vacuum leak. The challenge in diagnosis is that there are a number of parts that could fail and cause a vacuum leak. Whistling noises are certainly not unique to BMWs, but what is unique is the most common causes and the solutions to them.
Check the CCV valve
The BMW CCV valve has several different names, some people refer to it as a PCV valve, but the most common term today for BMWs is CCV and that is how I will refer to it. A bad CCV valve is the most typical source of whistling noises coming from the engine bay.
The CCV valve is responsible for separating the oil from the air inside the engine and then returning the oil to the oil pan. It serves this function to reduce pressure off of the crankcase. This is an extremely important role and without the CCV valve your BMW would leak excessive oil and build too much pressure in the engine.
Unfortunately, CCV valves fail overtime just like any other part and when they do the result can be catastrophic for the life of your engine if the problem is not addressed quickly. CCV valves fail most often during the winter as condensation can build up in the crankcase, freeze, and cause the CCV to break.
So how does a bad CCV cause a “whistling” noise? When the CCV valve fails, it can cause a vacuum inside of the engine which creates the whistling noise. Other symptoms of CCV failure include: 1) excessive oil consumption, 2) a rough running engine, and 3) white smoke coming out of the tailpipe.
CCV valves can sometimes be one of the easiest faulty parts to diagnose. Simply remove the oil cap while the engine is running. If there is a lot of suction holding the cap down and it is difficult to remove, then you likely have a CCV valve failure. JUST REMEMBER, you are removing the oil filler cap, not the oil filter cap. If you remove the oil filter cap while the engine is running you are liable to get covered in oil.
Replacement cost and difficulty varies depending on the model BMW that you have. I have replaced CCVs on E36s and E46s, and although it is not the most difficult job, it certainly is not the easiest. On these earlier models the CCV was separated from the valve cover so you only needed to purchase the valve and potentially a few hoses.
You can check out my article on replacing an E36 CCV valve here.
But starting with the F30 generation BMW began installing the CCV directly into the valve cover. This makes for a significantly more costly replacement, as you have to purchase a new valve cover along with a valve cover gasket just to replace a CCV valve. Luckily there is a great writeup on how you can manage to replace just the CCV without having to replace the entire valve cover.
Check for vacuum leaks
So what if you perform this basic test and there is no suction holding down the oil filler cap? Well the next most likely cause of a BMW whistle noise is a vacuum leak.
By far the most common vacuum leak I have encountered, at least in the context of it being large enough to cause a loud whistling noise, is a bad valve cover. Unfortunately, BMW valve covers are made of plastic and they have been known to crack over time. Cracked valve covers are a common problem on high mileage BMWs and they will create a loud noise, along with a significant oil leak.
Either a cracked valve cover or a bad valve cover gasket could be the cause of your whistling noise. Other symptoms are usually pretty easy to identify as a problem with the valve cover will also cause oil-related issues. Sometimes you will have a burning oil smell because the oil from the valve cover is dripping down the side of the engine block. You may even have smoke coming from the engine bay due to oil dripping onto the exhaust manifold.
If you have a valve cover problem and your symptoms include a burning oil smell or you actually see smoke, you should stop and turn off the car immediately. Oil dripping onto the exhaust can cause a fire!
Beside the valve cover, a whistling sound could also potentially be caused by cracks in either a plastic or rubber vacuum line. One of the most common hoses that crack and cause noise is the crankcase breather hose which attaches the valve cover to the CCV valve. Due to its location, this plastic hose gets a lot of heat from the engine block and it commonly cracks overtime.
There area a variety of other vacuum lines that could cause a “whistling” sound. After checking the CCV, valve cover and crankcase breather hose, the next best thing is to use a smoke machine to try and locate a vacuum leak. If you do not have a smoke machine you can also try the cigar method or carburetor cleaner method. You can check out more details on these methods here.
Whistling noises are a common occurrence on older vehicles whether it’s a BMW or a Ford. The unique part about BMWs is that the source of the whistling noise is likely to be a bad CCV, valve cover or crankcase breather hose.
Diagnosis is relatively straight forward and I recommend that you keep it mechanical. Start by checking for pressure in the valve cover, then take a look at potential symptoms of a bad valve cover, check the crankcase breather hose, and finally run a smoke machine into the intake.
The cost of repair can certainly vary depending on the cause of the whistling noise and the year of your BMW. An easily accessible vacuum line or crankcase breather hose might cost you $20 plus a minimum labor charge, whereas a CCV or valve cover replacement can easily cost several hundred dollars.
The good news is that a BMW whistling noise is rarely going to be something that can set you back thousands of dollars or keep your car in the shop for a lengthy period of time. Most problems associated with a whistle are easily diagnosed and the repairs are usually within the scope of most DIYers.