How long should the engine be off until checking oil level?

Question

I have seen contradictory advice for checking oil level on the dipstick.

One advice is that the engine should be off for few minutes so that the oil has time to settle. The idea here is that the oil level should be checked when the engine (and the oil) is hot.

Another advice is that the oil level should be checked when the engine is cold.

Which of these two advices is correct? Should I check the oil level after few minutes from stopping the engine? If so, how many minutes is "few"? Or should I check the oil level as the first thing in the morning so that the engine is completely cold? What is clear to me is that you shouldn't check the oil level immediately after turning off the engine.

I assume that there may be two differences in these methods. For example, the engine and the oil may have different coefficients of thermal expansion. Also, checking the oil level when the engine is cold gives the oil more time to settle.

Answer 1

It depends on the car, some take longer (a few minutes) to drain back into the sump than others e.g. some Nissans or Subarus. The engine/oil needing to be cold to be checked is pointless the amount that would drain back versus checking after a few minutes is negligible.

Answer 2

Let me provide another answer, as this is too long to be a comment. The volumetric coefficient of thermal expansion for motor oil is 0.0007 per degree Celcius. So, from 0 degrees Celcius (it's cold in Finland!) to 100 degrees Celcius (the typical motor oil operating temperature) it is 0.07. For steel, the linear coefficient of thermal expansion is 0.000012 so the volumetric coefficient is 0.000036 and for 100 degrees Celcius it is 0.0036. So, the difference is 0.0664. This means that 4 liters of oil when cold seems to be 4*(1+0.0664) = 4.2656 liters of oil when hot. The difference of 0.2656 liters of oil can be compared to the difference in the high/low marks on the dipstick which is probably between 1 liter and 1.5 liters.

According to this calculation, it is clear to me that there is real difference in checking the oil level when hot and checking the oil level when cold. But this does not provide an answer to whether the engine should be hot or cold when checking the oil level.

Answer 3

Depends upon the auto manufacturer. But in general, due of the limits of thermal expansion of the oil, the random reading of the dipstick either way will not adversely affect whether or not to add another quart of oil.

Traditionally, the dipstick was tuned to read accurately when the oil was cold. Of course, that begs the question, “how cold is cold?” Alaska in the winter, or Florida in the summer?

Some manufacturers have tuned the oil dipstick to read accurately when the oil is hot - though given enough time for the oil to drip into the pan.

Answer 4

This is really something you should consult with your owners manual with on a per car model basis.

Neither advice is wrong per-say, because it depends on the way the engine was designed.

Most owners manuals should tell you exactly how to check the dipstick the way they designed it. Some vehicles may say only do it when cold, only when hot, some might say wait 4 minutes after turning off, some might say 10. It depends on how the manufacturer designed it, and what they actually want you to check.

However in a general sense. Cold or warm, I always wait 10 minutes, this allows the oil that is sitting in the upper sections of the engine to drain down, for an accurate reading of how much oil the engine has available to the oil pump. This may be incorrect for some vehicles so always check on a per model basis.

Answer 5

Per my Chilton guide for Chevy: With the vehicle on a level surface, run the vehicle for a few minutes. Allow adequate drain down time, 2–3 minutes, and measure the oil level.

Per the dictiomary: FEW definition - a small number of. "may I ask a few questions?" synonyms: a small number, a handful, one or two, a couple, two or three;