Are you sure they're supposed to?
Keep in mind the Dead Men sized those radiators to heat the room to a comfortable temperature on the coldest day of the year. That's the day during which the radiators should be hot all the way across. If the radiator you're working with isn't hot all the way across, check the room temperature with a good thermometer. If the room is the correct temperature, the burner is probably off. Without the burner there can be no more steam. And without more steam, the radiator can't possibly get any hotter than it already is. If the radiator is grossly oversized for the room, it may never get hot all the way across.
If the room is the right temperature, don't worry about how hot the radiator gets.
The room with the partially heated ONE-PIPE steam radiator is too cold.
If it's a one-pipe radiator, check the air vent. If the vent is clogged, the air can't get out and the steam can't get in. Painters do a real job on air vents.
Check the radiator's pitch while you're at it. If the pitch is wrong, there may be a buildup of water in the radiator. That will cause the steam to quickly condense before the radiator can get hot all the way across. If the pitch is wrong, the radiator will also gurgle and rumble and the vent will probably spit.
There may also be a buildup of sludge in the horizontal runout to the radiator's riser. That sludge will trap water, and the water will condense the steam before it reaches the radiator. A "panting" air vent is a good clue that you're having this problem.
Clean the radiator and, if necessary, the riser. And make sure you have the radiator pitched the right way.
The room with the partially heated TWO-PIPE steam radiator is too cold.
If it is, check the steam trap by opening it up. Take care not to get burned. If air rushes out of the trap and the steam races through the radiator, you know either that trap or a nearby trap is defective. Find it, and repair or replace it.
Never add an air vent to a two-pipe-steam radiator. The air vent will make the radiator hot, but if their steam traps have failed, the condensate won't drain from the radiator. You'll wind up with water hammer, further steam trap damage, higher-than-normal fuel bills, and severe water level problems in your boiler or boiler-feed pump receiver.
There is no substitution for steam trap maintenance.
Want more troubleshooting tips? Check out A Pocketful of Steam Problems (With Solutions!).