In effect, you're seeing how much oil is in the bottom of the engine (sump, etc) as that represents a constant and a good reference for measurement.

If you've had the engine running, the oil's been thrashing around all over the place and will take some time to drain to the bottom, thus meaning you get a false reading (and a different one every time you run the engine, as the oil will settle temporarily in different places inside the engine!) therefore representing a variable and useless for consistent measurement.

Always makes me laugh to see people measuring and topping up at the forecourt - garages love it though!

 

Normally I'd agree, except the manual tells you to check the oil each visit to the service station and I quote "Wait a few minutes after turning the engine off before you check the oil".

S

 

I knew I read it somewhere - As long as the car has sat for a couple of minutes then you should get around the problem of oil being thrown around the engine.

Also when the oil is warm are you not more likely to get a more acurate reading as it is more fluid?

I guess as long as its safely between the min and max then it probably does not matter that much.

 

Always check oil when warm and left for about 5 mins....most accurate reading as long as your level! After paying for yor petrol is ideal...as long as you dont mind a queue!

 

Well bugger me, I checked my oil last night and my dipstick has X's on both sides, but the H and L are only on one side so that's the side I use.

I've found the only way I can get a reliable reading is when the engine is cold, if the engine has been running the oil tends to run along the dipstick making it difficult to read. I reckon the manual only recommends checking it when you fill up for convenience, rather than it being the best method.