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So I recently purchased my first BMW not off to a great start. After I test drove it I noticed a small leak I told the dealer who then replaced it the valve cover gasket cover and assured me that was the cause. Not noticing anymore leaking I purchased it. That day I started to hear a very loud hissing noise only from inside and when driving. But it stops when I brake or even touch the brake. Also I noticed its leaking again. Whenever I park I take a peak under and there's always 4-5 drops on the driver side. And also I don't know if its just the fuel gauge but I just filled up with premium and my gauge is down almost 1/4 after 38 miles. Anyone having the same hissing noise or have a solution. Any ideas of what's leaking and could that cause poor mpg?
 

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So I recently purchased my first BMW not off to a great start. After I test drove it I noticed a small leak I told the dealer who then replaced it the valve cover gasket cover and assured me that was the cause. Not noticing anymore leaking I purchased it. That day I started to hear a very loud hissing noise only from inside and when driving. But it stops when I brake or even touch the brake. Also I noticed its leaking again. Whenever I park I take a peak under and there's always 4-5 drops on the driver side. And also I don't know if its just the fuel gauge but I just filled up with premium and my gauge is down almost 1/4 after 38 miles. Anyone having the same hissing noise or have a solution. Any ideas of what's leaking and could that cause poor mpg?
The hissing is probably the hose for the brake booster..... big black thing that's behind the brake fluid reservoir with a big hose coming out of it. Check the hose and all connections of it and I'm sure you'll find the hiss.

These engines can leak from a number of places once past 70-80k. VCG, oil separator (CCV) and hoses, oil filter housing gasket (leaves oil on the engine block "waffle" pattern behind the PS pump.

Your on board computer should tell you your mileage. Will need to reset to be sure. If you drive normally you should get near what the specs call for. If it's tuned up otherwise, failing pre-cat O2 sensors can cause crappy mileage. Recommended replacement around 100k.

Be sure to familiarize yourself with the e46 wiki link above your post too. Lots of good stuff in there in general.
 

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