What are the consequences of mixing 5w40 and 5w30 oils of the same brand?
3 Answers
The consequences may include inadequate engine protection, affecting driving performance, increasing engine operating resistance, causing insufficient engine power, and even impacting the engine's service life. Additional information: To protect the engine: It is recommended not to mix oils of different brands or specifications. When switching to another brand or type of oil, remember to drain the existing oil completely to allow the new oil to perform its functions better, thereby protecting the engine more effectively and extending its service life. Engine oils: Currently, there are three types of engine oils available on the market: mineral oil, semi-synthetic oil, and fully synthetic oil. However, fully synthetic oil is the most commonly used due to its superior quality and performance compared to mineral and semi-synthetic oils.
As a car owner who often does DIY maintenance, I think mixing 5w40 and 5w30 oils of the same brand isn't a big deal for short-term emergencies. Last time when I found myself short on oil during a road trip, I temporarily mixed half a liter of same-brand oil with different viscosity. After driving 200 kilometers, the engine sounded a bit muffled but the temperature remained normal. However, long-term mixing is definitely not advisable. Oil viscosity is like blood thickness - mixing them will compromise the engine's lubrication efficiency. The mechanic I know said this would accelerate component wear, especially for turbocharged engines which are more sensitive. If you really have to mix oils, make sure to change to fresh oil within two weeks. Don't follow my friend's example who kept using mixed oil for over half a year and ended up spending nearly 10,000 yuan on major engine repairs.
I deal with over a dozen engine maintenance cases daily and have witnessed numerous instances of mixed oil usage. The most immediate consequence of blending 5W40 and 5W30 oils from the same brand is the failure to meet viscosity standards. While 5W30 is designed for the precise clearances in new engines, 5W40 better suits the wider gaps in older engines. Mixing them creates an in-between viscosity that's neither here nor there. This compromised oil blend often leads to noisy hydraulic lifters, unstable crankcase oil pressure, and in severe cases, abnormal camshaft wear. Last month, a Tiguan owner who mixed these oils for three months found sludge buildup throughout the valve cover when the engine was opened. Although base oils from the same brand are similar, differing additive ratios can actually promote sediment formation when mixed.
