The most important thing to look for with a 400E is engine temperature. Does
the car run hot? A hot running engine is a common problem with these cars.
The usual fix for this problem is a modifcation to the fan clutch metallic
strip to cause the clutch to engage at lower engine temperature. That said,
you probably don't want to buy a car that has been running hot for long because
the front and rear main seals and other parts will be cooked. Drive the car
and see what temperature it is running at on the highway. It should be running
at no more than 90 C. Personally, I believe part of the reason for the hot
running 4.2 liter engine in the 400E is that the 124 body is too narrow to put
a large radiator in. You can make it thicker but not wider. Although, this
helps it would likely help more it was both thicker and wider. Issue number two
is timing chain wear.
These engines often have timing chain wear. The timing chain path is pretty
long and you can have the chain checked for wear. If you have much timing
chain stretch you should have the chain replaced.
Another thing you should know about that engine is that it has two
distributors. Somewhat complex considering the fact that the post '95 E class
cars don't even have a single distributor. I wanted to buy a 400E or a '94 -
'95 E420 (the cars have nearly the same engine except the E420 runs at 11 to 1
compression. The 400E runs at 10 to 1). Nearly every car I drove ran very
hot. I ended up buying a '95 E320 wagon. I don't have a distributor and it
runs cool. Of course the E320 engine has other problems but I've been lucky so
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