That should do it but it’ll take a long time for air to get past the jiggle valve in a closed thermostat. The plug I’m talking about is just inboard of the #1 injector. Looks like it takes a 17mm wrench.

IIRC all M10x and OM60x blocks have a coolant drain behind the starboard engine mount arm, It’s where Diesels have a block heater and turbo oil supply port. I suppose they’re generic bosses on gassers. Or do gassers have block heaters? The fitting is like a giant brake bleed screw that takes a typical garden hose so you can direct the effluent.

Sixto
98 E320s sedan and wagon