[W126 Coupe] What do you think?

[Gerry Van Zandt]

Sounds to me not so much of a compression issue, but rather like you  
have leaking valve stem seals. Common issue when the motors get around  
the 150K mileage and higher. Mine (also an '89 SEC) has had it since I  
bought the car with 147K on it. It always used about a quart or quart  
and a half of oil every 2,000 miles, but really didn't leak much. I  
could NEVER figure out why, but it was certainly using oil  
somewhere .....

Several months ago (the car just turned 179K today) I saw a small puff  
of blue smoke in my side rearview mirror as I pulled away after  
standing at a stoplight for a while. Classic symptom of leaking valve  
stem seals -- watch carefully after you sit for a nice long stoplight,  
or idle in your driveway for a couple of minutes, then "goose" the  
throttle while the transmission is in P or N.

What happens is that the oil leaks downward (underneath the cam  
covers) past the guide seals into the chambers, where it gets burned.   
It's a relatively easy repair, most shops can do it for about  
$400-600. Parts are only about $40. If you're a medium to advanced DIY- 
er, you can do it yourself but you will need a couple of inexpensive  
special tools.

Usually new seals will solve the problem for a few years, but it's  
only a Band-aid approach to really what should be done -- the heads  
being pulled and refurbished completely. Of course, this is a $3K-plus  
job so most folks tend to go with the inexpensive "Band-aid".  The  
only risk with just doing the guide seals, is that when the technician  
gets in to replace the seals, that they find one or more loose valve  
guides.

If you have even a single loose guide, it's automatic "time to pull  
the head and have it totally refurbished" time.  No ifs, ands or buts.  
I'd say a decent percentage of the time, a tech will indeed find a  
loose guide -- perhaps 30-40% of the time. So it's a bit of a gamble.

The good thing about pulling the heads is that you can re-seal them  
with new head gaskets (rear corner oil weeping onto the exhaust  
manifold is a very common issue with the 560s), and freshly guided &  
valve-ground heads will probably give you a nice 8-10% HP boost. Of  
course, replacing the heads means you'll likely also have to replace a  
lot of the top-end soft parts -- hoses and the like, which become  
brittle with age and heat, and will crumble or tear once you "tear"  
into the head removal.  So be prepared to pay several hundred (if not  
$400-500) for parts -- intake & exhaust manifold gaskets, head  
gaskets, cam cover gaskets, seals, guides, hoses & vacuum lines, etc.

I hope this helps.  Just watch for the little puff of blue smoke  
behind the car after you have a nice long idle, or start up from a  
nice long stoplight.

Cheers,
Gerry
The Woodlands, TX



On Jul 14, 2009, at 11:15 AM, mbcoupes-request at mbcoupes.com wrote:


> Message: 4

> Date: Tue, 14 Jul 2009 07:19:46 -0700

> From: "Kirby's" <apkirby at comcast.net>

> Subject: [W126 Coupe] What do you think?

> To: <mbcoupes at mbcoupes.com>

> Message-ID: <5E9E8C5496464749966F651A120C2874 at DJ8JXD51>

> Content-Type: text/plain; format=flowed; charset="iso-8859-1";

> 	reply-type=original

>

> 1989 560 SEC, 140K miles

> just started using quite a bit of oil. No leaks on the ground.

> Spark plugs look OK

> Seven cylinders measure 155 for compression

> Second cylinder back on the drivers side measures 95

> What do you think is wrong?

> How do I determine for sure?


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