Well that was short-lived, back to overheating. Exactly the same behavior prior to the thermostat change.

Engine is running good, slightly rich actually.

Timing is good, no detonation or pinging, vacuum retard disabled.

Fan clutch is locking up at operating temp, shreds a rolled up newspaper.

I'm getting frequent high excursions of temperature on the gauge, greater than 100˚, but less than 120˚. Once the engine has fully warmed up, it refuses to run less than 100˚, even on a cool day. Using an IR gun, my inlet temp at the upper radiator neck is 220˚F, but the outlet at the bottom is only 160˚F, that seems like an unusually large temp split to me.

When I had the thermostat housing apart before, the little "burp" port on top was clogged shut. I managed to get it cleared out and can only assume it's clogged up again. Looked online for a replacement housing, and it looks like they're either NLA or astronomical in price! If that burp port is clogged, would it make sense that the thermostat is getting airbound and not functioning correctly? Anyone had any success cleaning one out and keeping it working properly? Am I barking up the wrong tree?!

Until I get this hot running issue straightened out, the car is staying parked, I'm not interested in blowing head gaskets!

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]