How to get stable and long lasting high temperatures in charcoal grill? 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?
I'm not sure how many steaks you're doing at once, but if you're not using the entire grill surface, stack the charcoal up. (Not sure how well it'd work with the entire grill surface and, e.g., two starters full of charcoal. With the grill open, it'll surely work.)

You can cook steaks with the lid off, that'll likely lead to the coals burning faster (hotter).

Stacking the charcoal does two things:


the stack is higher, so it gets the charcoal closer to the meat. You can't lower the grate on a Weber kettle, unfortunately.
there are more briquettes under the meat, each putting out heat.


A good stack is hot enough to brown a steak, even if you put it on the grill dripping with marinade (not that you should). Make sure to have a pair of tongs, you won't want your hands anywhere near it.