Hey guys. So about two months ago I purchased a 94 E220 Estate. I got the car very cheap but in a fully running condition, legally on the road etc. I took the car in as a project to work on over the winter. I knew the engine was leaking oil which came down to a head gasket but that has all been fixed.

Yesterday I noticed a relatively loud knocking sound coming from the thermostat area (Top of the engine near water pump). It is loudest when engine is cold but quietens down when warm.

After stripping down the engine to the pistons this is what I've done so far:
Got the head shimmed by a shop
Got new head gasket and bolts
Got new exhaust and intake gaskets
Got new rocker cover gasket along with spark plug seals
Have all new spark plugs
New oil (Castrol GTX 10W40)
Flushed the cooling system and added new antifreeze
Replaced a bearing on the serpentine belt tensioner along with a new belt

The engine is running really nice as it should except for that knocking sound. The temperature stays just above 80 and everything looks good. Only one thing I noticed is that the air vents in the middle don't seem to be pushing hot air, only the ones on the side do. Any help would be appreciated

 

I can't speak to the so called knocking, knocking and location of knock means many things to many people, trying to suspect location and cause without the ole coat hanger(probe) sound test---however regarding cold and hot air distribution--you really need to read the manual or search because once you do you won't lose any more sleep over the supposed air distribution---quite possibly you have been driving Citrons too long.

 

It's definitely coming from near the thermostat/water pump area. As for the vents I know the middle vents are not suppose to be distributing hot air, didn't really spend much time inside the car yet!