How often do I need to top up my car's engine oil? When I check the dip-stick, I never seem to get the same oil-level mark each time, so I am not sure how much to top up or if I need to at all.
Engine oil should be checked using the dip-stick only when the engine is cold and the car is on level ground.
In any case, the engine must have been at rest for at least half an hour. This is because the dip-stick literally dips into the oil sump and if the correct level is to be measured, the oil needs to settle.
Oil is pumped up to various parts of the engine when it is running, so there would be little oil in the sump to measure immediately after the engine is turned off.
Pull out the dip-stick and wipe it clean before observing the maximum and minimum marks. Then, insert it back fully into its sleeve before pulling it out again.
You will be able to see a definite strip of oil at the end of the stick and check if it is below the maximum.
If you need to top up, pour in no more than half a litre to avoid the risk of over-filling and then check again later.
Generally, a well-maintained car engine should not require oil top-up between service intervals. It will begin to consume engine oil only after about 180,000km.