求翻译：1.教练车换机油，要针对当地最低温度换相应牌号的机油，国内牌号和国外牌号目前在市场上混杂使用，限于篇幅不在这里一一介绍，目的是使机油在较低和较高的环境温度下黏度能保持恒定（相对）:是什么意思？

1. coach-for-oil, against local minimum temperature for the corresponding grade of motor oil, domestic brands and brands currently on the market abroad mixed use, due to limited space does not describe here, so that viscosity of oil in the low and high ambient temperatures can remain constant (relative):