ive looked around before posting this question and so far ive seen follow the upper radiator hose and the thermostat is behind the housing. idk if thats true, but on my 91 d1.5b something or other its not there. i must have to follow the lower hose but that doesnt look right. i just wanted to double check before i started pulling other stuff apart and find that its not there

 

It should be there behind the thermostat housing at the end of the upper hose. Are you sure you are looking at the upper hose? The upper hose is actually the one attached to the lower part of the radiator. It goes towards the back of the engine.