How To Flush A Motorcycle’s Wet-Clutch After Using Car Motor Oil

A reader asks: I recently changed oil in my motorcycle and mistakenly used car engine oil. I knew there was something wrong when the clutch started slipping early into rides. Is there a flush that can be used to get all of the automotive oil residue out of the clutch? Can this clutch be salvaged?

Our answer: As the reader has learned, it is a massive no-no to use oil designed for automotive engines in motorcycle or ATV engines/transmissions that have a wet-clutch. The friction modifiers in car engine oil cause the clutch plates to slip and eventually glaze. Once the clutch plates are severely glazed, the clutch will slip regularly and will have to be replaced.

Do not use chemical engine flush products in an attempt to remove the friction modifier from the clutch plates. This can do more harm than good to your clutch.

A better option is to change to a motorcycle-specific oil (which will not contain friction modifiers). Run at low loads for an hour or two and then change the oil again. Run this batch for another hour. Then put the engine under moderate load to determine if the clutch slips. If it does not slip, the clutch may be fine. If the clutch does slip, then you will have to change the clutch plates.

We’ve heard of a few cases where clutches have been salvaged after short intervals of wrongly using automotive engine oil. Assuming that the clutch plates are not badly glazed, the method of flushing with a motorcycle oil may be worth a try. However, there are no guarantees that the clutch can be saved.

Why Is Car Engine Oil Bad For Motorcycle Clutches?

Friction modifiers are included in automotive engine oil formulas to reduce friction and improve fuel economy. However, these friction modifier ingredients cause motorcycle wet-clutch plates to slip and ultimately fail.

Both conventional and synthetic car motor oils are equally bad for motorcycle transmission use.

Do Synthetic Motorcycle Oils Cause Clutch Slippage?

Neither synthetic or conventional motorcycle oils employ friction modifiers. Therefore, they are safe for wet-clutches. Despite synthetic motorcycle oils having the attribute of reducing friction, they do have the correct frictional properties for wet-clutches. In fact, synthetic motorcycle oil is arguably better for clutches as it can reduce operating temperatures.