First, I'm very sorry you are experiencing this kind of problem - I don't recall anything similar being reported on the forum in the past 10+ years. I agree that the intake manifold is an unlikely culprit; especially since I don't think there are any coolant passages near the #7 intake runners. But, the intake is one of the first things to come off if the heads are removed, so that could be checked before digging deeper. Coolant could be entering the intake and causing the smoking in general, but probably not just on cyl #7.
I don't want to tell your shop how to do their job, but IMO before tearing into a 35 hour project, I'd at LEAST start with the following:
- Compression test on hot engine (1 hour labor tops)
- Leakdown test on cyl #7, and any other cylinder out of spec
- Pressurize cooling system and use borescope to look in cyl #7 to absolutely confirm liquid is entering
Assuming worst-case scenario, coolant is getting into #7, you have a few possible options. It boils down to either:
Pulling the heads, and hope the problem is confined to the heads, not the block. If so, it would make sense to at least have the heads disassembled and checked out - mostly confirming the valve guides are OK. Do both sides - labor/cost is incremental to pull the other side once the first head is off. Cams/lifters/springs should be fine. At least replace the valve stem seals if the rest is good. The next problem is, if one head is cracked (causing the coolant entry), you probably need to replace it, unless a REALLY good shop is confident they can weld it. Besides labor and machine shop work, parts will get expensive for this - especially if paying full retail, or if the shop marks up above retail. Total cost, um, I'm trying not to do the math.
Replace the engine. Good used M119's are available very cheap, some patient shopping should find you a nice low-mile motor. I'd estimate $2k or less including freight for a really nice donor .972/.974 from a 500E or SL500, under 100kmi, verified clean inside, compression tested, etc. The used motor will need some TLC prior to install - all upper chain rails, maybe a chain, new VC gaskets, front crank seal, maybe rear crank seal, etc. You could swap some of the existing recent components over from the old motor (i.e., PCV hoses) if desired; the new caps/rotors, also swap the ETA since it's known-good. Labor to R&R the motor should be in the 12-hour ballpark, on top of labor to freshen up the used motor. You could then put the old motor on an engine stand and tear into it when you have spare time, as a science experiment. In THEORY, the cost should be similar or less, due to fewer labor hours. Even lower if you do the work on the donor engine yourself (it's easy on the engine stand). And you get to keep the original motor. In late summer 2015, someone else in the Bay area did this, there is a long thread (click here
) with details on what was recommended for the donor motor... although I suspect the engine pretty much got dropped in as delivered from the dismantler. (?)
If it were me... I would choose option #2, but I understand if timing issues may not allow that. The risk with #1 is that you could be out 15-20 hours labor before they discover the engine isn't fixable, or not worth fixing (very, very unlikely - but possible); and then you move into option #2 anyway.
About the incremental work - since the car had an awful lot of items replaced when the engine/trans was removed last time, there shouldn't be much needed. Wouldn't hurt to eyeball the engine mounts, new Lemforders are <$100 each. All the hoses and general engine bay stuff should be ok. I'd see what the shop recommends and compare their recommendations against the prior records to see if/when something was last changed.
A third option would be to consider going nuts and buying/building a 6L motor. Jono had worked up an estimate for someone recently to build a fresh one (not cheap), or you could look for a used one overseas to import (may take a while). A variation of option #2 would be a rebuilt long block from Metric Motors (click here) but at $10k for a stock 5L - ouch, ouch, ouch. I haven't checked prices but I assume a dealer rebuilt long block would be even worse. IMO, the ROI is not good on a rebuilt 5L... if spending that much I'd go for a 6L.
I'm still hoping the shop finds something simpler if they stick a camera into cyl #7 and/or prove the coolant isn't going in there from a cracked head or failed head gasket...