Thermostat Fix, 1984 Mercedes 300D, W123

Procedures to replace the engine thermostat. If your engine isn't getting up to temperature then this is the most likely solution.

[@charlesrockwell3923]

Good advice to replace the drain plug. You neglected to mention that in addition to getting the thermostat mounted with the spring facing the block, you also need to align the dot on the thermostat so that it is at the top. I have no idea why Mercedes does this, but if you don't get it right, the car will run too hot. If you look at a genuine Mercedes thermostat you will see a dot or an arrow and the word "top", and this should be at 12:00 when installing the thermostat.

[@Meb123]

Specifically on the OM617 (300D) thermostats, if there is no vent hole ( I have never seen one with this hole), then orientation (dot or mark location) does not matter. The venting of possible air is taken care of by the bleed hole in the housing not the thermostat. That's why Wahler thermostats for the OM617 don't even put a mark on their thermostats.

[@michagrzegorczyk5342]

Thank you for this very helpful video. I replaced thermostat in my 2.4d and it was very similar

[@sonofprince4124]

Did you use the other rubber gasket also? I have to recheck mine after seeing this video and make sure I put the spring facing into the car the right way. haha The vehicle should run hot if its installed backwards, correct?

[@davutyalcin-]

Nice video man I have a w115 240 diesel 3.0 Can you give me advice wich kind of thermostat i have to buy? Because there are several types of thermostats

[@tydale8629]

MAHLE ORIGINAL TX2080D Thermostat Insert I think