Maintaining oil drain intervals to those established by OEMs is always recommended because they know how each of their vehicles engines performs in the field. Always consult the owners manual for oil specification and drain interval. Premium quality motor oil will maintain its effectiveness over the life of the drain without a significant drop in engine protection. Some key elements of motor oil and additive packages and the potential results of their depletion are detailed below:

Anti-wear additives lay down a protective, sacrificial film between moving parts, thus the additives are consumed during the life of the oil change. These additives also help stop oxidation of the motor oil which also causes them to be consumed. Changing the oil not only refreshes these additives, it also removes dirt and other contaminates from the engine.

Dispersants grab dirt and sludge before they can build up during engine operation. As the oil absorbs more debris, it needs to be changed or deposits will form. Changing the oil also helps prevent sludge deposits in the valve deck.

Detergents are consumed as they help keep high-temperature surfaces such as pistons clean. Changing the oil in proper intervals will help to prevent ring sticking and piston deposits.

Anti-oxidants stop oil oxidation and help keep the oil from becoming too thick. Properly functioning oil helps prevent loss of fuel economy, prevents sludge and varnish deposits and helps maintain proper low-temperature pumpability.

Oil plays a major role in heat transfer in the engine. As oil ages and becomes thicker, it loses some of its ability to cool the engine. Changing the oil helps prevent piston deposits and helps cool moving parts.

Engines generate acids, which can cause corrosion. These acids eat at soft bearing surfaces and yellow metal used in bearings, oil coolers and other parts. Changing the oil helps keep corrosive wear to a minimum

Each engine consumes different parts of the oil at varying rates; therefore, it is not possible to establish a universal oil drain interval. It is always recommended that OEM drain intervals be followed.

Courtesy of Pennzoil

Head Bolt Installation Tips

Make sure all the head bolts are in perfect condition with clean, undamaged threads. Dirty or damaged threads can give false torque readings as well as decrease a bolts clamping force by as much as 50%! Wire brush all bolt threads, carefully inspect each one, and replace any that are nicked, deformed or worn. If a bolt doesnt thread into a hole smoothly with finger force alone, theres a problem.

On aftermarket studs or bolts, never use a die to recut the threads. Most have rolled threads, which are stronger than standard threads. Use a thread chaser to clean up the threads.

Dirty or deformed hole threads in the engine block can reduce clamping force the same as dirty or damaged threads on the bolts. Run a bottoming tap down each bolt hole in the block. The tops of the holes should also be chamfered so the uppermost threads wont pull above the deck surface when the bolts are tightened. Finally, clean all holes to remove any debris.
If the block deck has been resurfaced and you are using studs rather than head bolts, chamfer the top of each hole.

For head bolts that screw into blind holes, lightly lubricate the bolt threads, as well as the underside of the bolt heads with engine oil. Make sure the bolts do not bottom out or hydrolock because of oil trapped in the blind hole.

For head bolts that extend into a coolant jacket, coat the threads with a flexible sealer. Failure to coat the threads may allow coolant to leak past the bolt.

Because TTY head bolts are permanently deformed once they are tightened, they should not be reused. Reusing TTY bolts will cause them to stretch further, which increases the risk of breakage. A stretched bolt also will not hold the same torque load as before, which may cause a loss of clamping force resulting in head gasket leakage.

Check bolt lengths. Make sure you have the correct length bolts for the application and for each hole location (some holes require longer or shorter bolts than others). If a bolt is too short and only engages a few threads in the block, it may pull the threads out of the block.

Bolts should also be measured or compared to one another to check for stretch. Any bolt found to be stretched must be replaced because it may be dangerously weak, it wont hold torque properly, and it may bottom out when installed in a blind hole.

When installing head bolts in aluminum cylinder heads, hardened steel washers must be used under the bolt heads to prevent galling of the soft aluminum and to help distribute the load. Make sure the washers are positioned with their rounded or chamfered side up, and that there is no debris or burrs under the washers.

Resurfacing a cylinder head decreases its overall height, so be sure to check bolt lengths to make sure they wont bottom out in blind holes. If a bolt bottoms out, it will apply little or no clamping force on the head, which may allow the gasket to leak.

If a head has been milled and one or more head bolts are dangerously close to bottoming out, the problem can be corrected by either using hardened steel washers under the bolts to raise them up, or by using a copper head gasket shim in conjunction with the new head gasket to restore proper head height.

Always look up the specified tightening sequence and recommended head bolt torque values for an engine before installing the head gasket. Never guess. Complete cylinder head torque specifications for domestic and import vehicles can be found in service manuals and torque tables published by gasket
manufacturers.

Use an accurate torque wrench to tighten
standard-type head bolts in three to five incremental steps following the recommended sequence and torque specs for the application. Tightening the bolts down gradually creates an even clamping force on the gasket and reduces head distortion. Its a good idea to double-check the final torque readings on each head bolt to make sure none have been missed and that the bolts are retaining torque normally.

Note: If a bolt is not coming up to normal torque or is not holding a reading, it means trouble. Either the bolt is stretching or the threads are pulling out of the block.
With TTY head bolts, use a Torque-To-Angle Indicator gauge with a torque wrench to achieve
proper bolt loading. Dont guess on the angle. Be exact.

If a head gasket requires retorquing (most do not), run the engine until it reaches normal operating temperature (usually 10 to 15 minutes), then shut it off. Retighten each head bolt in the same sequence as before while the engine is still warm. If the engine has an aluminum cylinder head or block, however, dont retorque the head bolts until the engine has cooled back down to room temperature.

On some applications with retorque-style head gaskets, it may be necessary to retorque the head a third time after a specified time or mileage interval due to the design of the engine. Follow the vehicle manufacturers recommendations.