M117 viscous fan coupling
Recently I had noticed the 560SEC running hotter than usual in traffic. This was during winter when it was quite cold outside. I suspected that the original viscous fan coupling was starting to fail. I was able to spin the fan quite easily just after I turned off the engine while it was hot.
Back in 2020, I had a similar issue on my 560SEL and changing the viscous fan coupling fixed it. Back in 2020 I used a Behr/Hella coupling and paid USD$160 plus shipping. The Behr/Hella coupling was made in China and a fairly different design from the original Fichel & Sachs unit. So far it is still working well on the 560SEL. However this part has now been discontinued so it wasn’t an option.
The part number for my car is 116 200 11 22. It looked like I had four options. I could get HT (Hamburg-Technic) for about USD$80; URO Parts for about USD$110; Meyle for about USD$140 or Genuine MB for about USD$550.
None of these options were great. I had never heard of HT, URO is a brand I try to avoid unless there is no other option at all, and Meyle is also a brand I avoid, but prefer it to URO. I’ve read of pretty high failure rates for cheap viscous fan couplings. Mostly these failures were the coupling no longer cooling well, but I found a couple where it had locked on and caused other issues. Genuine was less likely to have these issues, but USD$550 plus shipping is going to up towards $1000.
After debating the way to go in my head for a few days, I noticed that the Genuine had gone on sale at FCP Euro for $395. Still expensive, but much more realistic. I bought one.
Today I went to fit it. Its a very easy job on the W126. I spent far longer researching clutch brands than fitting the new one. Unlike the Behr/Hella unit from 2020, the genuine part looked identical to the original. It was made in Germany by Horton rather than Fichtel & Sachs. It was manufactured in 2014, which makes me wonder if this part will go NLA after current stock runs out.
The viscous fan coupling is attached to the pully with four 10mm bolts. They are quite easy to remove with a long spanner. To get enough clearance to remove the fan assembly, the radiator shroud should be loosened. It does not need to be removed. I normally remove the three bolts closest to the top and leave the bottom one unscrewed but not removed. This makes installing the new coupling easier.
Once the fan unit is out, there are also four 10mm bolts holding the viscous coupling to the fan. Plus my original fan coupling was stuck to the fan after so many years and needed a few taps with a rubber mallet to get it off.
There really are not any tricks to re-install the new viscous fan coupling. It just bolts back in like the old one, plus the radiator shroud is re-attached. I had the whole job done in 30 minutes and I am very slow when working on cars.
