W211 Thermostat housing bolt - can anyone tell me what bolt it is?

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Nov 28, 2007
Gave the new car its first service (by me) today. I replaced the thermostat at the same time as it seemed to be running cool. After the job already having taken too long due to having to run out and get the special tool for the oil filter, to my horror, when doing up one of thermostat housing bolts the ratchet went limp.

The bolt had sheared and I figured I was going to have to drill it out which would have involved removing a lot of bits that were in the way. Fortunately when I removed the housing I had about 2mm sticking out to play with, just very little room, but it came out eventually.

Don't want to drive it to Merc tomorrow as it is and the Mrs will be using her car so hoping I can get a suitable bolt at the local fasteners, just need to know what bolt it is. If anyone has EPC or has found themselves in the same predicament and can tell me the bolt measurements are that would be much appreciated.


Can't help with the size Dan, but worst case scenario is to take out one of the other housing bolts for comparison.
Have you any spare bolts in the garage you can just try .Thats till you can replace it at a later date?.Find a nut that will screw on to the other bolt you removed .Then use the nut to find a bolt the same thread..
Nine times out of ten it will be metric fine on cars. Without seeing it I'll guess m6 fine .
Doubt I have a suitable bolt in the garage, they're pretty small. I could take one of the others out but the oil filter is back in now and there isn't much clearance.

I have the broken bits of the bolt which the man at the fasteners can probably use to find a replacement but seeing as I'll be running the few miles there and back I was hoping to phone to see if he had it first.

I used to live next to a proper 'four candles' hardware shop in the middle of nowhere and had no idea how it survived, but I never went in there and came away without what I wanted. It seems a lot harder to find a specific bolt or what have you now and even specialist fasteners seem to mainly have these overpriced packets of bolts in limited sizes rather than boxes of every conceivable size and shape of fastener you cpuld imagine.

Anyway, just thought I'd check if anyone knew!

You need the proper bolt as the housing is not threaded from new, so you will end up messing up the housing with a random bolt. Hold out for a few days and order the correct bolt.
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No mention of what engine is in the W211:confused:

If a M112 or M113 petrol then need a coarse thread torx bolt obtainable from Mercedes'

If you managed to break that bolt then either plenty of corrosion or you definitely need to use a small torque wrench.
Wasn't thinking of using a random bolt.

It's an E220 cdi. No corrosion, torque wrench required, but what's the torque?
Put a little grease on the thing on fitting it , and it will come out easy next time. Or do as others think is right and have it shear off again next time .Or if you dont have grease use thread lock.
It came out fine. I sheared it tightening it back up.

Merc don't have the bolt but I have the size now. M6x25 (well done streethawk). They come with a 10mm head so hopefully it'll fit.
I would torque it to 8 to 10 Nm, no need for grease or thread lock - its only holding a thermostat in place and the rubber gasket will seal it effectively.
I would torque it to 8 to 10 Nm, no need for grease or thread lock - its only holding a thermostat in place and the rubber gasket will seal it effectively.

In the end I didn't bother. I put it on relative loose with the intention of tightening it up should it leak but seeks okay. Proper bolt ordered just in case which will be swapped out when it arrives in a few days.

Thanks for the help,


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