Its the washer that doesn't allow oil to leak from engine. Just like rubber washer used in water pipe fittings.
As engine oil gets worst after long run (i.e after 7500 KM's), the washer also does (i.e Due to high temperature of engine) and also the old washer will be flattened when the bolt is tightened previous.
Left side is old washer which is flattened and right side new washer. The same will be worst if the old washer is rubber based.
So its better to replace to new one on every oil change. It doesn't cost much either and there will be no doubt of oil leakage.
Thought it might help a few of you guys that want to fiddle around with your own car.
List of materials:
Oil - Read your owners manual for what oil to use and how much your sump can take.
Oil filter - Again, it's usually listed in the owners manual.
Sump plug washer - Preferably a genuine one, ask your local mechanic, he'll sort you out.
Oil drain pan - To collect old oil into.
Funnel - or even a bottle cut open will do the job.
17mm socket - to undo the sump plug
The actual process is pretty simple really.
So I strongly recommend using axle stands or even stones under it as long as it's stable.
Step 3: Drain the old oil out. Use a 17mm socket/spanner and crack the sump plug bolt loose, and undo it by hand slowly. Take it off and let the oil drip into the drain pan, you can use any sort of container,
Step 4: Replace the sump plug washer with a genuine new one.
Before screwing on the new oil filter, spread some oil on the rubber seal so that it sits tight when you tighten it, also fill up half of it with new oil before putting it on.
Hand tighten the oil filter, don't over tighten this. Screw it on till the rubber seal makes contact and from there make another 2/3 turn.
5: Fill up with new oil as per manufacturers specifications. Constantly keep checking the dip stick, bring it close to the full level but DO NOT over fill it.
and that's it, you've just done an oil change on your car :)
Hope it helps, and as always, if you have any questions, feel free to ask.
My questions are:-
1. Is the spanner size mentioned, same for all cars?
2. Is it necessary to change sump plug washer each time?
3. Is the amount oil to be poured mentioned in manual and sold for that amount only? Actually I want know, how to be sure that tank is not over filled or short. Do I have to rely on dipstick measurement only?
4. Why oil filter is filled half with new engine oil before setting it in?