The fuel system cleaning service offered at quick-lube facilities — typically involving a bottle of cleaner added to the fuel tank and occasionally a throttle body spray treatment — is among the more contentious upsells in automotive maintenance. The service is sometimes unnecessary, sometimes genuinely useful, and the recommendation is almost never based on an actual assessment of the specific vehicle’s condition. Understanding what fuel system deposits are, how they form, and what genuinely removes them separates useful maintenance from profitable theater.