Checking Oil Hot or Cold should be similar on the dipstick ?

[zeroptzero]

I always thought the oil dipstick reading would be somewhat similar from cold to hot readings, but I have some difference on my new car.

If I read the dipstick cold after sitting overnight it is slightly under the full mark. I believe oil expands as it is heated, but more oil should drain back into the sump after sitting all night. When oil is hot it may expand but more oil remains in the upper areas of the engine 5-10 minutes after shutdown. In my mind it should be a wash but the oil level reads a bit higher when hot shortly after shutdown. I may try checking the oil level when warm, say 1-2 hours after shutdown, but not totally cold, and see how that compares.

What is the preferred method of checking oil ?

 

[Astro14]

Oil expands with temperature. So does transmission fluid, but in transmissions, the space is more constrained, so you get a greater change in level with the change in temperature compared with oil in a broad, wide pan.

The preferred method of checking rests with the maker of the engine.

My Mercedes, for example, doesn’t have a dips stick and will not let me check the oil unless the engine is both warm, and had been shut down for a certain amount of time.

 

[Shel_B]

Many/most/all vehicles have a recommended method described in their owner's manual. Have you checked your manual?

That said, whatever method you decide upon, consistency is the primary consideration.

 

[twX]

Oil is around 7% more dense at 15C compared to 100C, so the oil level will be lower when the engine is cold. For a 5L sump, that difference would amount to ~350 ml.

The other factor is the time it takes for oil to drain back to the sump. After the engine is shut off, the oil level will continually rise for at least several minutes. At some point, it will hit a maximum, after which it will continually decrease as the oil cools off and becomes more dense.

Taking readings with a cold engine on flat ground will be most consistent. The markings on the dipstick could be based on either warm oil or room-temperature oil, but will always be based on waiting some time for oil to drain to the sump.

The owner's manual for my Subaru just says to wait at least 5 minutes after the engine is shut off, which is ambiguous, but the service manual clarifies that the markings on the dipstick are based on a cold engine. I would always just assume that the markings are based on a cold engine unless the manual says otherwise.

 

[ATex7239]

I do it cold. I’m not particular about being exact and my vehicles don’t seem to be particular either. Cold drains and cold oil level checks seem to work fine for me.

 

[Kira]

Are you new to vehicle maintenance?
If you get your hands on different vehicles, you may encounter pulling oil up the dipstick tube.
This can result in wildly varying readings.

 

[riff1006]

I check it cold and drain it warm. No worries about oil in the tube and it drains maybe a little faster and maybe more thoroughly.

 

[TheOilWizard]

Cold or warm, never much of a difference in my experience. Maybe 1/8th" on the dipstick, if that.

 

[zeroptzero]

Are you new to vehicle maintenance?
If you get your hands on different vehicles, you may encounter pulling oil up the dipstick tube.
This can result in wildly varying readings.

I've been wrenching on my own cars for about 30 years , mostly as a hobby, I like tinkering on cars, no expert by a long shot. I have seen some wildly varied readings as you noted, I hate those.

I had a Honda S2000 that was nearly impossible to read the dipstick when the oil was new/clean, I had such a hard time reading that dipstick, and that dipstick had two different readings depending what side of the dipstick you were looking at. One side of the dipstick was always higher than the other side, and it was suggested you always go by the lower reading side, it had something to do with the angle of the engine and the metal splash shield that sat around the dipstick in the lower engine area.

On this car it was down a bit cold and up a bit hot, so it made me curious about the whole dipstick reading temp. Thanks for the reply.

 

[zeroptzero]

I check it cold and drain it warm. No worries about oil in the tube and it drains maybe a little faster and maybe more thoroughly.

When I check it cold the reading seems to be much clearer to read, less oil being dragged up the tube it seems , like you can get when it is hot.

 

[zeroptzero]

Oil is around 7% more dense at 15C compared to 100C, so the oil level will be lower when the engine is cold. For a 5L sump, that difference would amount to ~350 ml.

The other factor is the time it takes for oil to drain back to the sump. After the engine is shut off, the oil level will continually rise for at least several minutes. At some point, it will hit a maximum, after which it will continually decrease as the oil cools off and becomes more dense.

Taking readings with a cold engine on flat ground will be most consistent. The markings on the dipstick could be based on either warm oil or room-temperature oil, but will always be based on waiting some time for oil to drain to the sump.

The owner's manual for my Subaru just says to wait at least 5 minutes after the engine is shut off, which is ambiguous, but the service manual clarifies that the markings on the dipstick are based on a cold engine. I would always just assume that the markings are based on a cold engine unless the manual says otherwise.

Thanks this is an excellent bit of information for my question, thank you, it makes perfect sense. This is for a new Subaru. Knowing that the markings on the dipstick are based on a cold engine really helps, I find a cold engine oil reading is much clearer to read on the dipstick, when hot you get oil splashing and pulling up the dipstick tube etc. Thanks for the reply.

 

[oldhp]

However much the owners manual says to put in with oil filter is what I put in. I leave 1qt out to see exactly where 1qt low is. I check it the next morning. I add a qt and check it again the next morning. Now I know exactly where full and 1qt low is. I don't care where the oil is at on the dipstick.

 

[barkingspider]

I check my oil randomly. If it been sitting cold, I just make sure the level is at or very close to the full mark

 

[zeroptzero]

I check my oil randomly. If it been sitting cold, I just make sure the level is at or very close to the full mark

Having owned a Honda S2000 I know the importance of checking your oil levels. The rule of thumb was at least at every gas fill-up with those cars. That oil just disappeared pretty quick at times depending on driving conditions

 

[repairman54]

Today's engines with VVT have a ton of oil passages in them and oil filled components that the motors of old did not have. That is why they need extra drain time after being run so they fully drain down back into the oil pan for an accurate measurement.
Follow the hot or recently run oil checking information in the ''destruction manual'' for your engine, the manufacturer knows their engines.
The lines on the dipstick show the normal range, full in many engines may be at the midpoint of the sticks hash marks. If labeled some just say minimum and maximum.