radiator

You have found it's limits of heat transfer.

Either air is blocked from flowing through it (clogged fins with leafs, debris, bugs)

or

coolant is blocked from flowing through it (clogged tubes, in the old days - recore, now - replace)

__________________
Greg

1996 E300D 73k, 4k on WVO
1996 E300D 315k, 141k on WVO
1991 350SDL 249k, 56k on WVO
1987 190E 2.6 w/2.2 diesel, 40k on WVO (for sale after I replace the head gasket)
1983 380 SEC w/603 diesel, 8k on WVO (for sale)
Previous:
1983 240D, on WVO
1982 300D, on WVO
1984 190D (Deerslayer) on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)