The one one the left under the tensioner bolt is a temperature sensor used for glow plug duration. I can't recall the resistance verses temperature but I believe it can be found with a search. The other sensor on the right higher up is another temperature sensor used to control the auxiliary fans. In my case 92 e300d they are not interchangable.

I do know if you put a 1 k resistor in place of the glow plug temp sensor the after glow is maximum. If you do this and your engine runs normal until the after glow goes out it would point to perhaps pop pressures being wrongly set as was in my case.