One of the most common tasks to perform is replacing your engine oil. Frequent oil changes are supposedly the most important thing you can do to maintain and prolong the life of your engine. With the better oils that are available today, the requirement for frequent changes is diminishing. Even though BMW now recommends oil change intervals that are much farther apart than in the past, I usually recommend that you keep the changes under the 5,000-mile limit. If you don't drive your car too often, you should change the oil at least once a year to keep things fresh.
The first thing you need to do is to make sure that you have everything that is required for the job. Nothing is more frustrating than emptying your oil, only to find out that you don't have a replacement filter or enough oil. You will need an oil filter, a wrench, a roll of paper towels, a very large oil pan or bucket, and between 4-7 quarts of oil. You'll also need a 17mm or 19mm wrench to remove the drain plug from the bottom of the engine sump. Start by driving the car around, and letting it heat up to operating temperature. You want to empty your oil when it's hot, because the heat makes the oil flow a lot easier, and more particles of metal and dirt will come out when the oil is emptied.
Once you get the car parked, place the oil pan bucket underneath the oil tank of the car. At the bottom of the engine sump there is a plug that is used for draining oil. Remove this plug carefully, and make sure you have a very large oil pan--about 7-quart capacity--under it, with a drip pan under the oil pan in case you underestimate. The oil will be very hot, and will empty out extremely quickly, so be careful not to burn yourself. There will be no time to grab any more buckets or oil pans, so make sure that the one you choose is big enough.
This is a good time to remove the oil filter. You want to make sure that you remove the filter with the oil pan still under the oil tank because the oil filter is full of oil, and this oil will have a tendency to drip down out of the filter into the tank and out the drain hole. On E30 cars, the filter is a complete unit with a outer metal housing. This filter should only be screwed on finger tight, but you may need a filter wrench to remove it. If the filter is really on tight, you may need to resort to more drastic measures. One sure-fire way to get the oil filter off is to poke a long screwdriver through it and use the handle of the screwdriver for leverage. It doesn't matter that you are destroying the filter, because you are going to install a new one. Be aware, though, that this method will leak oil out of the filter into your engine compartment, so have some paper towels handy.
On the E36 cars, the filter is a cartridge-type filter which is contained within a metal oil filter housing. There is a cap that is located on top of the housing (it may require a small socket, or a large one depending upon your year). Remove the top, and underneath you will see the cartridge filter. Simply remove it from the oil filter housing. Have plenty of paper towels on hand, as oil will spill from the filter if you're not careful.
While all of your oil is draining, take the plug from the engine, and carefully clean it with a paper towel. The plug at the bottom of the engine is magnetic, and attracts all the little bits and pieces of metal that get trapped in the engine oil. When both plugs are clean, replace them in the car with new metal gaskets around the plugs. If you don't use the gasket, they will leak oil. Torque the two plugs to 25 Nm (18 ft-lbs) for the 17mm or 60 Nm (44 ft-lbs) for the 19mm drain plug.
Now head back into the engine compartment, and install the new oil filter. For the E30 cars, install the oil filter with the seal wet--wipe a small bit of oil on a paper towel, and use it to make sure there is oil on the seal all the way around the filter. Screw on the filter and make it snug tight. No need to use the iron grip of death when tightening the oil filter--these don't have a tendency to leak.
For the E36 cars, you should clean out the inside of the oil filter housing before installing the new oil filter cartridge. In your oil filter kit, you should also have two o-rings and a replacement copper gasket for the long bolt that attaches the top of the housing (early E36 cars). Replace the o-ring at the bottom of the long bolt, and also replace the large o-ring underneath the canister top. Insert the new filter into the housing, and reinstall the long bolt and the canister top. Tighten the top of the canister to 25 Nm (18 ft-lb).
Now it's time to fill up your BMW with motor oil. A lot of people aren't really sure what motor oil to use in their car. Traditionally, the characteristics of motor oil were linked closely to its weight. Heavier-weight oils protect well against heat; lighter-weight oils flow better in cold. In general, if you live in a cold climate, you should use a 10W-40 or similar oil. This oil is a 10-weight oil that behaves and protects against heat like a 40-weight oil. In warmer climates, you should use a 20W-50 oil. This oil doesn't flow as well at the colder climates, but gives an extra "edge" on the hotter end.
The question of whether to use synthetic or traditional "dinosaur" oil often comes up among car buffs. Consumer Reports (July 1996) ran an extensive test on the two types of oil, altering amongst many different brands. The testers installed freshly rebuilt engines in 75 taxicabs, and then ran them through the harshest conditions on the streets of New York City. Placing different brands, weights, and formulations in the cars, they racked up 60,000 miles on the engines, tore them down, measured, and inspected the engine components for wear. The oil was changed at 3,000 miles in half of them, and the rest were changed at 6,000 miles. results: regardless of brand, synthetic or dino, weight, and oil change interval, there were no discernable differences in engine component wear in any of the engines. Their conclusion? Motor oils and the additives blended into them have improved so much over the years that frequent oil changes and expensive synthetics are no longer necessary.
Still, some people swear by synthetic oil. In practice, I don't recommend using synthetic oil if you have an older car with old seals in the engine. There have been many documented cases in which the addition of synthetic oil has caused an otherwise dry car to start leaking. If you own an older BMW that doesn't have fresh seals in the engine, I would stick to the non-synthetics.
Fill your oil tank from the oil filler hole in the top of the valve cover, located in the engine compartment. Add about 4 quarts to the engine, and check the dipstick. Continue to add about a half a quart at a time and keep checking the dipstick. Fill it up until it reaches the top mark of the dipstick - the engine oil level will automatically lower when the oil filter fills up with oil. Make sure that you put the oil filler cap back on the top of the valve cover, otherwise, you will end up with a messy engine compartment when you drive away.
Now, start up the engine with the hood open. The oil pressure light should stay on for about a second or two and then go out. Hop out of the car and look at the engine compartment, then take a quick look underneath the car. Verify that there's no volumes of oil seeping out of the engine. Now, take the car out for a drive and bring it up to operating temperature. Shut the car off and then recheck the oil level (careful, the car will be hot). At this point, I like to top the oil off at the top point on the dipstick. Make sure that you dispose of your old oil at a respectable recycling station.