Temp Issue

Riffian

I BBQ'd some pork tenderloins yesterday. I set the lower and top vents to get around 400 degrees. But, I noticed that my temp were running low, about 275/300 degrees. The only way get the temp up was to almost fully open the vents. I've never experienced this problem before. Before cooking I cleaned out the ash box and made sure no vent holes were blocked. 

Any ideas? 

theyolksonyou

How long since you 1. Calibrated your thermometer and 2. Pulled the firebox and cleaned the little piles of ash around the perimeter? Also, fresh lump or used?

Riffian

Thank you. I've never calibrated the thermometer. That's on my to do list this week.