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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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Old 02-10-2011, 10:45 AM
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Flug540 Flug540 is offline
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Location: Hayward, CA
Join Date: Nov 2009
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Mein Auto: 1998 BMW 540i 6-spd
E39 540i low compression

Hi guys,

I'm in the middle of what I thought it would be a valve cover gasket replacement and a few other relatively simple maintenance jobs, but the deeper I go the worse it becomes. First I noticed leaks from the head gaskets (yet to be confirmed). Yesterday I measured cylinder compression and it turned out evenly low in all cylinders at about 130psi as opposed to 170-203psi per spec (I've seen a post from one guy who measured his to be at 205 in average!). It was late at night and I didn't get a chance to do a wet test. I left the battery charge overnight just in case and will retest it again today followed by the wet test.

I read that if the wet test significantly and evenly improves compression it means worn piston rings, is that true in most cases?

My car is 1998, but only has 80k miles on it, is it a bit early for the piston rings to go? In the time that I owned it (a little over a year) I added roughly 10k miles on it and it never overheated.

Unless I'm missing it, I don't see a procedure for piston ring replacement in Bentley (if it comes to it). I haven't checked TIS yet, not sure if it has it. Where can I find the procedure explained in detail?

Any thoughts or suggestions are always greatly appreciated!

Here's a video of one of the cylinder tests, does it sound normal?

Thank you, guys, for any input!
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