If your vehicle is showing thick grease splattered on the inside of the wheel well or tire, here are the most likely causes and the parts you'll need to fix each one.
The rubber boot protecting the constant velocity (CV) joint has torn or dry-rotted. As the axle spins, centrifugal force flings the thick, dark moly grease out of the joint and all over the inside of the wheel well and suspension components.
If the CV axle or boot was recently replaced, the metal retaining clamp may not have been crimped tightly enough. This allows grease to seep past the edge of the boot and splatter when driving.
During a recent service, a technician may have pumped too much grease into the zerk fittings on the ball joints or tie rod ends. The excess grease squeezes past the dust boots and splatters onto nearby surfaces.
The protective rubber dust boot on a ball joint or tie rod end has ruptured due to age or debris. While it holds less grease than a CV axle, it can still splatter thick grease onto the inner wheel area.
On older vehicles or heavy-duty trucks with serviceable wheel bearings, the inner wheel seal can fail. This allows wheel bearing grease to escape and coat the inside of the tire rim and lower wheel well.