What causes high engine RPM but no increase in speed?
3 Answers
The reason for high engine RPM but no increase in speed is: automatic transmission slippage, which may also be accompanied by severe wear or even burning of clutch or brake friction plates. If the automatic transmission is slipping, the owner should not rush to disassemble it. Instead, various inspection tests should be conducted first to accurately identify the true cause of high RPM but no speed increase. First, check the fluid level of the automatic transmission hydraulic oil. If the fluid level is too low or too high, it should be properly adjusted, and then observe whether the automatic transmission is still slipping. If it still slips, the quality of the hydraulic oil should also be checked. If the hydraulic oil appears brownish-black or has a burnt smell, it indicates that the friction plates of the clutch or brake or the brake band are burnt. In this case, the automatic transmission should be disassembled for repair.
Last time I drove a manual transmission car, I encountered this situation where revving the engine in neutral sent the RPM soaring to four or five thousand, but the speed stubbornly refused to exceed 60 km/h. Upon inspection, it turned out the clutch disc was worn smooth, causing slippage and preventing power from reaching the wheels. If this happens with an automatic transmission car, it could be due to aged transmission fluid or a clogged valve body, causing the transmission to get stuck in a low gear. Another time, a friend's car had a completely clogged catalytic converter, restricting exhaust flow, resulting in high RPMs but no power output. Additionally, damaged driveshaft universal joints or abnormal tire pressure can also lead to power loss. It's advisable not to floor the accelerator if you encounter such issues. Instead, stop promptly to check for warning lights and visit a repair shop as soon as possible to read the fault codes with a diagnostic computer for the most reliable solution.
My old car had this issue before - when I floored the accelerator on the highway, the tachometer would shoot up but the speed would get stuck at 80 km/h. The mechanic said there are three common causes: clutch slippage preventing power transmission, internal pressure leakage in the transmission causing gear shift failure, or a severely dirty throttle body restricting air intake. Especially for automatic transmissions, problems often occur if the transmission fluid hasn't been changed for too long. Additionally, severe engine carbon buildup and worn spark plugs can also affect power output. For this situation, it's recommended to first check the engine oil and transmission fluid condition. If basic maintenance doesn't solve it, professional diagnostics will be needed.
