I have Weber one touch spherical grill (18.5") and trying to cook steaks with direct heat. I place steaks when grill thermometer shows 450-500F, but after 2 or 3 minutes temperature starts dropping and after turnover it can be 400F and continue dropping fast. Briquettes near the edge getting cold but briquettes in center still going.
I have tried with lump charcoal and Weber long lasting briquettes using chimney starter, yesterday I held briquettes in starter for 30 minutes, and briquettes were very hot and well burning, but got same temperature issues.
All vents are fully open, lid closed. What am I missing?