miles and hours between oil changes can be greatly reduced.  Refer to the service manual for exact intervals. To change the engine oil, warm the engine to full operating temperature. This will help suspend debris in the  oil  and  make  the  oil  drain  more  thoroughly. Unscrew the drain plug and allow the oil to flow into a catchment pan Be careful of hot oil; it can cause painful burns. Usually the filter elements are replaced at the same time the oil is changed. The most common filters are the spin-on filter or replaceable element type oil filter. Spin-on, throwaway oil filter—replaced as a complete unit. Unscrew the filter from the base by hand or a filter wrench and throw the filter away. When replacing, wipe the base clean with a cloth and place a small amount of oil or grease on the gasket to ensure a good seal. Screw on a new filter, tightening at least a half a turn after the gasket contacts the base. Do not use a filter wrench because the filter canister could distort and leak. Replaceable element oil filter—removed from the filter housing and replaced. Place a pan underneath the filter to catch oil from the filter. Remove the fastening bolt and lift off the cover or filter housing. Remove the gasket from the cover or housing and throw it away. Take out the old element and throw it away. Clean the inside of the filter housing and cover it. Install a new element and insert a new cover or housing gasket (ensure the gasket is completely seated in the recess). Replace the cover or housing and fasten it to the center bolt securely. After the oil has been completely drained and the drain plug replaced, fill the crankcase to the full mark on the dipstick with the proper grade and weight of oil. Start  and  idle  the  engine.  Check  the  oil  pressure immediately. Inspect the filter or filter housing for leaks. Stop the engine and check the crankcase oil level and add to the full mark. Oil  Pump  Service Service on oil pumps is limited since they are relatively trouble-free. An oil pump will often still be operating  trouble-free  when  the  vehicle  is  ready  for salvage. A bad oil pump will cause low or no oil pressure and possibly  severe  engine  damage.  When  inner  parts  wear, the pump may leak and have a reduced output. The pump shaft can also strip in the pump or distributor, preventing  pump  operation To replace the oil pump, it is first necessary to determine its location. Some pumps are located inside the engine oil pan Others are on the front of the engine under a front cover or on the side of the engine. Since removal procedures vary, refer to the manufacturer’s service manual for instructions. Most  mechanics  install  a  new  or  factory  rebuilt pump  when  needed.  It  is  usually  too  costly  to completely  rebuild  an  oil  pump  in  the  shop.  Before installation, prime (fill) the pump with engine oil. This will  assure  proper  initial  operation  upon  engine starting. Install the pump in reverse order of removal.  Anew gasket should be used and the retaining bolts torqued as specified by the service manual. Pressure Relief Valve Service A faulty pressure relief valve can produce oil pressure problems. The valve may be located in the oil pump, filter housing, or engine block. If symptoms point to the pressure relief valve, it should  be  disassembled  and  serviced.  Cleaning  and adjusting is all that is usually required.  Remove the cup or cap, holding the pressure relief valve. Then, slide the spring and piston out of their bore. Measure the free length of the spring (length of extended  spring)  and  compare  it  to  the  specifications.  If the spring is too short or long, install a new spring. Some manufacturers recommend checking spring tension. Use a micrometer and a small hole gauge to check the valve and valve bore wear. Also, check the sides of the valve for scratches or scoring. Replace the parts if any problems are found. Assemble the pressure relief valve. Make sure that the valve is facing correctly in its bore. Slide the spring into place. Install any shims and the cover plug or cap. Refer to the service manual for details. The pressure relief valve may be adjusted in one of two ways. One way is by an adjusting screw (having a jam or locknut) which adds or relives pressure on the spring. The other way is by adjusting shims that are added  or  removed  to  adjust  opening  pressure  of  the relief  valve. 6-36