How to find air leaks in a crankcase ventilation system

  • 2005 BMW 325I
  • 125,000 MILES
Check engine light is on. Read codes. 2 of them. Bank one and bank two running lean. Looked up common causes on web. Vacuum leaks, dirty or bad mass air flow sensor, fuel filter ( low fuel pressure ), o2sensors.
So I started off with checking hoses. Found hose from oil pressure valve to oil pan melted almost in two. Which explains why I have been smelling oil burning, but never have had to add oil between oil changes. Every 5000 miles with Mobil one. I also found hose across top of engine leaking from front to rear right next to fuel rail. Also small hose coming from bottom of engine to air filter boot, hooks in after mass air flow sensor. I replaced those 3 and the hose from end of valve cover to oil pressure valve.
Cleaned mass air flow sensor with proper spray.
K+N air filter which I keep very clean. Don't use there oil. I cleaned throttle body last week. Looks good inside out. I need to chance fuel filter.
Have had car a little over a year. Put almost 25,000 on it since then.
Car looks and runs good. Get lots of compliments on it. 28 to 30 mpg on hwy and 22 or so in city.
I also found a small coolant leak doing this work yesterday and today.
Looks like it's coming from line coming into a small vented box looking thing under radiator on drivers side. What is that, haven't looked it up yet.
Also found small oil leaks on pass side of valve cover.
I installed some nice plus when I got car and I pulled them out yesterday and dint look great. Looked like plugs that were older then that. Not a issue sign in wear thou. Brown with a little gray on tip ends. Was a little oil around base of 2 of them because of those leaks. Not much thou.
Also poured some chevron fuel system cleaner with fill up today.
Thanks for any tips.
Saturday, October 15th, 2011 AT 6:10 AM

1 Reply

  • 3,380 POSTS
The vacuum leak you had would not cause you to loose much oil because of where it was. Smoe may have splashed out but not a lot of oil ends up there as it is not pressurized it only drains into oil pan via gravity. The valve cover is baffled so it will hardly ever loose oil if anything is even missing like the filler cap or hose.
You might ry to tighten the valve cover bolts, but only very, very slgihtly. When you do so, work your way from the inside bolts out in an alternating cross pattern like you would do a star tightening pattern for the lug nuts on youor wheels. I can't emphasize the word, "little" enough when you tighten them either as you will end up crushing the gaskets and making them leak more than they are now. If it is not to bad, you might want to leave it alone for a while and get new gaskets. They are probably failing more due to age than mileage and synthetic oil is so slick it tends to leak very easily pas gaskets and seals that are not perfect, as compared to regular oil, as synthetic is so slick and the viscosity does nto change much with temperature changes. I don't usually have valve cover torque pattern diagrams as the torque is in inch pounds, not may people have the little screwdriver to do such a small torque, and the pattern is pretty standard.

I don't have a diagram of it but the box on the side of the tank is a, "Seperate Coolant Expansion Tank", was the only description given.

A tan/brown color is just how plugs should look on a healthy engine.

If you need anyting else, just let us know.
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Saturday, October 15th, 2011 AT 7:06 AM

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