Many owners will swap the 1.1 Bar rated radiator cap that comes stock on the XR650R for an aftermarket unit. The goal is the prevent the radiators from boiling over as easily. It’s a somewhat debated topic in that using a higher pressure cap will increase the strain throughout the entire system. Most have positive experiences with switching radiator caps. Personally, I prefer to keep mine stock.
The SRC (Scott Summers Racing Components) unit is rated at 1.6 Bar and is part number 1672. It looks like this: