My '95 E300 was behaving similar. It has a dual auxiliary fan set up. If either of your cars have similar, I'd heartily recommend removing the fan shroud from the front and cleaning out the accumulated leaves and dead bugs etc. which are trapped between the lower half of the shroud and the condenser.

Another common place for junk to get trapped is between the condenser and the radiator. I like to remove the radiator, spray that out from the backside with a garden hose, and also spray out the condenser from the back. Repeat whenever you have a cooling problem.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC