The temperature difference between the bottom rack and the top rack of a dishwasher can vary depending on the dishwasher model and its specific design. In general, the bottom rack tends to be hotter than the top rack during a dishwasher's wash cycle.
The heating element of a dishwasher is usually located at the bottom of the machine. During the wash cycle, this heating element heats up the water, and the hot water rises, creating a warmer environment in the bottom part of the dishwasher. As a result, items placed in the bottom rack may be exposed to higher temperatures than those in the top rack.
Items labeled as "top rack safe" are typically made of materials that can withstand lower temperatures and are less prone to deformation or damage when exposed to the relatively cooler environment of the top rack. Placing these items in the bottom rack could subject them to higher temperatures, potentially leading to warping, melting, or other forms of damage.
Manufacturers often provide guidelines regarding which rack is suitable for specific items to help users avoid potential issues. To ensure the longevity of your dishwasher-safe items and to prevent any unwanted deformations, it's essential to follow these guidelines and place items in the appropriate rack as indicated by the manufacturer. Additionally, if you're unsure about a specific item's dishwasher safety, it's best to hand wash it to avoid any risk of damage.