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Particularly the black ones, they are unprotected and start to rust immediately when exposed to outside air. 4 of these style are now the current part numbers for the 6.9 water pump, and the 4 screws for the thermostat housing cap. Piss poor MB, Piss poor.

Here in Australia we have access to zinc plated or galvanised bolts and washers of all sizes made locally which are of superior quality. I will not be ordering any more external nuts and bolts from MB if i can source them locally. if not, they will be additionally galvanised or cadmium plated.

So they're not even zinc plated? What a waste of time... are there any markings on the bolts, such as manufacturers?

Tim

 correct, there all shit, just using water to wash the engine for any reason will start them rusting like youve dropped them into the ocean. Waste of money.

Use stainless! If you are buying them a few at a time the cost is negligable and they won't rust! PS You can always spray them black if the originals were and you want them to match!

I'm a very big fan of stainless steel, infact, i wish the whole w116 body was made out of it 

I find the selection very limited around here with stainless bolts - there are a small selection for marine applications but other than those, finding the correct size and type would be exceptionally difficult. Otherwise id always use them

Currently, only my complete exhaust system and tow ball are stainless steel, that I've done anyway. 

And another reason why I buy the majority of my screws and bolts in Germany. Of course, it helps that I am there reasonably often, but the selection is fantastic, and you can get the "correct" type. Price is also considerably cheaper as well. One example. The screws that hold the chassis plate on are EUR 0.62 each from the dealer in Germany. From the company I use, EUR 0.022 each. Is that profitering or what !

Hi Patric,
black bolts are often hardened to 12.9 quality and can not be hot dip galvanized (not electro galvanized either I think) because of the heat destroys the hardening.
Normaly the highest quality of hot dip galvanised is 8.8 which gives a yield strength of 640 MPa. This is to be compared with the yield stregth of 12.9 bolts; 1080 MPa.
The torque stated for bolts often use 70% of their yield stregth, so if you use 8.8 bolts you are probably damn close to overload them f you tighten them to the specs.

/Niclas

I received my bolts from the dealer recently. Two of them were black class 10.9, the rest were class 8.8 galvanised and one zinc plated. The washers were also hot dip galvanised. I'm actually quite impressed so far.

Tim

Does anyone know if zinc plating affects the strength of the bolts at all?