Can Old and New Transmission Oil Be Mixed?
2 Answers
Old and new transmission oil should not be mixed. Here are the consequences of mixing old and new oil: 1. Reduced oil pressure: This causes the oil in the transmission to thicken, leading to hindered internal heat dissipation and excessively high oil temperatures, thereby shortening the lifespan of the transmission and drivetrain components. 2. Slippage phenomenon: If the transmission oil is not replaced, the vehicle may experience weak acceleration when starting, resulting in frequent slippage during driving. 3. Accelerated wear: Prolonged failure to replace the transmission oil can lead to oil degradation and evaporation under high-speed and high-temperature conditions, causing rapid wear of components and damage to internal transmission parts.
I personally believe that mixing old and new transmission fluid is a bad idea. From my own experience, there was a time when I was lazy and didn't buy enough new fluid, so I topped it off with some old fluid. As a result, the transmission soon started to shift roughly and eventually cost me thousands in repairs. The different viscosities of old and new fluids may lead to uneven lubrication; additive conflicts can cause deposits or oxidation, accelerating internal wear. Old fluid also carries contaminants that can pollute the entire system and affect performance. This risk is especially high in automatic transmissions. When changing the fluid, be sure to completely drain the old fluid and use new fluid of the same brand and type, following the manual's maintenance schedule. Don't risk major losses for minor savings—safety first.
