wwh396

it sounded like a belt squealing so i replaced the belt ,tensioner, water pump, alternator, and both idler pulleys but squeal would return when engine reached operating temp. so i tried running engine without the belt and that is when i discovered that the engine is sucking air through the oil cap and dipstick tube. when you try to take the oil cap off it is hard to pull up as the sucking is strong but when the cap is off the noise stops what causes this and how to fix it? 2014 glk350

formerjeepguy

Some vacuum in the crankcase is normal and needed for vapor extraction. Most cars have a positive crankcase ventilation valve (PCV) that connects between the top of the valve cover to the intake and manages the vacuum level. I'm not sure what it is called by mercedes. Maybe crankcase ventilation valve, maybe centrifuge cover? You may have a problem with this valve. Or maybe not. It's hard to trouble shoot these things over the internet with terse problem descriptions. Do you have a check engine light or any problem codes?

tripper80

my oil cap has noticeable vacuum, removing the cap leads to higher idle rpm and more audible engine tapping sound. I think it's normal.