Weber OTG 26.75 Temp Drop

Hello,
Need some help obtaining linear temp through the whole cook process. Using charcoal only I have started my fires with an old electric heater that does a good job of getting the fire burning. I've set for 75% direct, 25% indirect for veggies. After carefully sorting the charcoal in the direct area the heat across the whole charcoal area is very consistent. I let it settle in around 20 minutes before I load any meat. The initial temps according to the Weber thermometer are super hot, around 475. I have always left the bottom vents fully open and closed the top vent to ~50% open. When the temp drops it does so quickly and opening the top vent fully does not seem to help much. Temp drops to below 300 and really doesn't go much past 300. I am thinking of starting my Q's with more charcoal but really I have been starting with a fairly heavy load of charcoal. I have also considered adding more charcoal to the back area where the grate lift is. But this bugs me cause I know the temps should climb nicely in the back and the front area of the coals will be much colder. Should I remove the whole hot grate loaded with meat then add the coals? I really don't want to have to remove a hot grate loaded with meat due to the mess it may create and the ease of getting my meat contaminated with whatever happens to be around.

I really wish there was an adjustment for grate height as it would enable you get a more even sear if you flip your meat at the middle of the cook.

The answer is most likely simple but I could use some help from the Weber folks.

One other question if I may. I keep all of the coals from directly touching the side of the grill. I don't want to ruin the finish on the kettle. Does anyone else do this?

Thanks!

Thanks tremendously for the responses. This place is great, getting help from others who have the same cookers is invaluable.

I have been cooking on a horizontal offset the last 1.5 yrs then prior to this many years on a Bandera. It appears I am going to need some time to get the fire right.

I use grate level thermometers on my offset so the Weber top thermometer is very different to get used of.

BTY, I always use a full chimney of briquettes to start the fire for my offset using the very large Old Country chimney. I have used the electric starter for my Weber because it works well and is what I have used for grills for many years. I start a lot of coals. Dampness of charcoal may be a problem cause I live right on the coast. Everything gets wet outdoors. Downstairs where I store stuff I have to use a heater in winter and a air conditioner in summer to keep that room above dew point. It's a major PIA.

I have never seen anything written on the the accuracy or longevity of the Weber thermometer. I am guessing that their accuracy is more than adequate for the job. I wonder if anybody has felt a need for upgrading the mechanical Weber thermometer with a mechanical thermometer they feel is superior. I have no interest in using electronic thermometers except for my Thermapen.

Thanks again for the help!