The thermostat housing bolts up to the block on your OM616 just like the OM617. I took the housing off when I got my 240d because I had a leak there as well and found out that the part where the housing fits up to the short heater hose was broken. I too got a piece of heater hose from the local auto parts store and cut it to the proper length. I didn't/don't have a gasket between the housing and the block either and it doesn't leak there. For some reason, I thought I remember seeing a gasket in the parts diagram at the dealer parts dept.

After all this, my new hose still leaks which I attribute to my broken housing. How bad is the hose? Maybe tightening the two hose clamps will fix the leak.

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1980 240D
1993 300D 2.5
2002 Golf TDI