E38 M62 OSV / PCV – black smoke!

2000 BMW 740iL - problem – clouds of blue smoke everywhere on startup!  The internet and it’s dog will tell you this is a classic problem with the M62 V8 engine – failure of the PCV (positive crankcase ventilation) at the rear of the intake manifold.  There is a thin rubber diaphragm inside this component and if it tears the engine vacuum will draw oil through the breather pipe into the intake manifold, where of course it will be burned off and produce blue smoke.  Specialist BMW mechanics were also sure this was the problem even though my PCV looked ok…

New part was bought and fitted (extremely difficult to remove the old one as the hex bolts all stripped).  No difference!  I was so convinced this was the problem I bought a second PCV – official BMW this time instead of the Meyle part.  Still no difference.  Time to dig deeper.  You can Google elsewhere for full instructions on removing the intake manifold – but basically just unbolt stuff – you can then remove the fuel rail and wiring loom and suspend it above where it used to be - you do NOT need to disconnect the fuel line to do this.

Look at the amount of oil that had collected in the manifold!  Now to remove the right hand side valve cover and the piece that goes along side, called the upper timing cover.  This reveals the cam shaft and chains.  There was a horrendous mess of congealed oil everywhere inside the engine – it was as if the previous owner had never done an oil change

What we’re looking for is the oil separator valve (OSV) – as the name suggests this separates oil in vapour form coming from the crankcase back to liquid through the use of an air pressure change in the cyclone – liquid drops back to the sump and the air is pulled through to the intake manifold.  You can just about see the OSV in the right picture below – it’s buried pretty deep behind the chain but it’s the VANOS rail in particular that makes access difficult.  After cleaning up some gunk it became clear the piece of plastic connecting the top of the cyclone to the breather pipe was cracked, which effectively rendered the cyclone useless – so liquid oil as well as vapour was being pulled up through the breather pipe to the manifold – no wonder some much collected there!

At this point I admit I did not replace the OSV – to do this really requires removal of the lower timing cover – essentially the front of the engine – and that requires the oil pump to be removed along with water pump, auxiliaries, locking the cams with a special tool I didn’t have, removing the chain tensioners, etc.  You can now imagine why this would be $4000 or $5000 in labour costs at a specialist mechanic (and you probably shouldn’t trust a non-specialist with the VANOS/cam system!).  So instead I fashioned an in-place repair of the broken pipe piece – using some high temperature hosing and high temperature epoxy resin.  I wasn’t really sure this would work but when I put everything back together it worked!  I sold the car over 2 years later and it was 100% fine all that time – no reason to believe it’s not still fine.  Absolutely zero oil burning.  The horrendous oil gunk I found under the valve cover also seemed to no have no effect – the engine remained extremely smooth and powerful.