1998 Toyota 4Runner Owners Manual - Page 226

4RUNNER (1998) Twin ground electrode spar plugs (5VZ- FE engine) The diluting ingredients evaporate out when the vehicle is then driven at high speeds, as on an expressway, making it appear that oil is excessively consumed after driving at high speeds. IMPORTANCE OF ENGINE OIL LEVEL CHECK One of the most important points in proper vehicle maintenance is to keep the engine oil at the optimum level so that oil function will not be impaired. Therefore, it is essential that the oil level be checked regularly. Toyota recommends that the oil level be checked every time you refuel the vehicle. NOTICE Failure to check the oil level regularly could lead to serious engine trouble due to insufficient oil. For detailed information on oil level check, see "Checking the engine oil level" in Chapter 7- 2.