When you purchase the used car, make sure that the engine has no damage. For that it is worth to carry out a small check by opening the hood. First of all, start the car and check if there is any vibration from the motor. Its presence indicates a defective engine mount. Inspect the battery to ensure that there is no rust on the terminals. With the engine running, look at what color the smoke comes out of the muffler. Normally it should be colorless or slightly white. The smoke of blue, black or too thick indicates that there are problems with the engine. After the engine has been running for a while, check the space under the hood for leakage of oil and other technical fluids.