Smoking exhaust--help diagnosing!
 

After a hard drive today, I noticed steam/smoke wisping out from under Ilse's hood. She blew a heater hose recently, so I figured it was a coolant leak. Howver, when I popped the hood, I found that it was smoke coming from the rearmost part of the exhaust manifold, right where it joins the downpipe. I just started running B100 and my injector return lines are kind of oozy, but this smelled like oil. Also, the exhaust manifold is discolored like it's soaked in oil, just right at the back. I had noticed this before, but written it off to the remains of some long-ago leak, as pretty much every part of the engine was a greasy mess when I bought it.

Any ideas, fellow dieselers? I don't see anywhere oil could be dripping onto the manifold. The back of the engine looks pretty wet, the bellhousing seems to be covered, but I haven't noticed a puddle on the pavement where I park, so I assumed that also was expected quarter-million-mile engine mess.

Ugh. Further examination reveals leaking from the valve cover gasket. Oil is seeping from the gasket, oozing down the side of the block, and then dripping onto the hot EM.

So now I have a few new questions:
1. How long do I have before the gasket gives out and makes Big Problems?
2. What is involved in replacing the gasket, is it a DIY job, and are any special tools required?
3. Could this be the cause of my suddenly-terrible fuel efficiency?

No one can predict how long your Head Gasket is going to last.
Look in the repair links below and see if there is info on the job you want to do and decide if you are up to it.
Also it is possible that the Head may need to be resurfaced. If the Machine Shop does not do it you will need to remove the Prechambers and install them with the proper protrusion.

DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

Try to tighten the 4 bolts of the valve cover equally but do not overdo it as you might destroy the seal. If you have a torque wrench, use it. I forgot how much torque is needed. It is quite easy to replace the seal. Have the proper length of fuel return hose as you will likely damage some of it when you remove the valve cover. Check the gaps of your valves while the valve cover is off as this could also be a source of poor fuel efficiency.

Not sure how we got from valve cover gasket to head gasket. Valve cover gasket replacement is a pretty easy job. It's already failed given your description of the amount of oil.

Valve cover gasket replacement is fairly simple on the OM606 NA engine, no crossover to remove.

Disregard checking valve gap check, the '86-up cars have hydraulic lifters.

@kerry: I originally said head gasket, then edited my post when I realized my error.
@babymog: The NA 606 unfortunately does have the crossover pipe. :/
I've been needing to clean it and my intake manifold out anyway, so this will just give me the kick in the ass to get it done.

Do I need to drain the oil before replacing the gasket?

nope. you can change the gasket with all oil intact. it's best to wait for all the oil to drain out of the head before you pull it, but a hot engine is difficult anyway, I'm sure you will do that.
you might wanna park on a steep incline to get as much oil as possible out of the way, but it's not criticle, as there is a pretty steep wall in the 606 head. (the 617 is practically flat! )

oops, i thought it was a 617

HA! It turns out that my valve cover gasket is fine, I just had injector return lines that had turned to Swiss cheese. Brittle, frangible Swiss cheese.
There's a drain hole at the back of the injector cover, right aft of the crankcase ventilation PCV. The copious amounts of diesel leaking from the injectors (I sucked 8 ounces out of the injector wells with my MityVac) was pouring out of this hole, run ing down the side of the head and onto the hot exhaust manifold, where it vaporized.

The fuel running down the side of the engine made it look like oil was leaking from the valve cover gasket. I also had noticed that it smoked more when I drove aggressively. From this I had assumed that the presence and quantity of smoke was related to exhaust gas temperature (and that the leak was constant), rather than increased fuel flow through the injector lines when I opened the throttle.

Problem solved! Hopefully this will help someone in the future.

Symptoms: volatile-smelling smoke/vapor from under hood, fuel smell in AC, rough idle when started cold, loud acceleration, rough/jumpy running in reverse, soggy/unresponsive throttle
Solution: replace decaying injector return lines damaged by biodiesel