I just got done doing this not too long ago. Apparently, there were two different water pump manufacturers and they put the thermostat in 2 different locations. If the piece on the left of your water pump right by the alternator bracket has two outlets, one going up and the other going down, your thermostat is on top of the water pump, like many cars. This would be an extremely easy bolt off bolt on deal.

However, if the piece on the left of the water pump only has one outlet (which points down, where the lower hose connects to), your thermostat is behind it. A little harder to get to, you're right, very tight. In this case, I took off the alternator bracket. Just loosen the belt, slip it off, undo the cc actuator rod and set the whole works over to the side. Then I simply unbolted, switched out t-stat, and bolted back up again the t-stat housing. As Ali said, put the checkball at the 12 o'clock. Also remember to use a new o-ring. Then just bolt the alternator housing back on, reinstall and tension your belt, pop on the cc act. rod and you're done. Also remember that you'll have to drain and refill the radiator.

Hope this helps.

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."