“That’s why you should never use them and only go to an independent! My guy used to be a dealer Mercedes tech, but he doesn’t work for them anymore so here’s a lot cheaper now!” -the previous owner of an E63
Well turns out that former Benz tech did head bolts on this engine, but applied Teflon sealant to them. Which is dumb for a number of reasons. 1) applying anything to threads of a fastener changes the torque reading and there only specs published for this are “dry” (quotes because they’re in coolant on this engine). 2) because the main body of the bike goes through the coolant jacket so the thread sealant is absolutely useless in this application.
This car came in not running. The engine appeared to be seized as it couldn’t be turned over by hand with a 3ft breaker bar. Removing the spark plugs freed it up though. Turns out the cylinders were full of fuel and coolant. It was hydrolocked. We cleared the cylinders out and got it running again, but it didn’t run right. After a few minutes it turned the coolant reservoir into a mini volcano!
So we tried to do a block test to see if there were hydrocarbons in the cooling system which would indicate a compression leak, probably from a failed head gasket. Even after pulling a gallon out of the cooling system if still turned into a volcano in a matter of minutes from dead cold. You can’t block test a volcano.
Engine teardown required. Mr. Former Benz tech was a real winner. He applied crap sealant all over a bunch of gaskets that don’t need and shouldn’t have sealant on them. I say it was crap because it felt exactly like the stuff that holds the fake key onto dealership propaganda, or fake credit card or whatever junk mail. Never came across anything like that before! Of course they were leaking.
But the real fun started when I got to the head bolts. Expecting them to be the old style, I was surprised to see they had been updated. The updated one don’t fail, and if the bolts don’t fail then the gaskets don’t fail. Now u was a little worried about my diagnosis up to this point and the future viability of this engine.
Grabbed my 3ft breaker bar and threw my weight at the first bolt....
Crap! Just about slipped and whacked my face against the engine! That bolt was so loose I could’ve taken it off with a 3/8” ratchet. And seven more were the same way! That’s when I found the sealant on the threads. Well, there’s your problem! *Insert meme here*
But this engine was hydrolocked. Surely it couldn’t have come away from that unscathed, right? So I went ahead and measured all the piston heights because that would tell me if there was a bent connecting rod.
Any guesses?
It’s an M156.
....
...
...
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Nope! All within .1mm of each other! And not a single tiny scratch on any of the cylinders! On mere mortal engines hydrolocking often renovates the house and adds new windows. But not on this!
Reassembled everything and she runs perfect!
Moral of the story, not all dealers are evil, and not all independents are worth using. You usually get what you pay for. And maybe there's a reason that mechanic USED to work for Mercedes but doesn't anymore?
Side notes: yes those are aftermarket headers. They’re very very nice. They are why I had to remove the engine out the bottom of the car though. Normally they would stay on the heads during head removal, but that wasn’t possible in this instance and the fasteners aren’t accessible with the engine installed on this design. It sounds glorious.