Check oil level cold or warm?

[Hokiefyd]

Sometimes, it does matter.

For example, with the Cadillac Northstar engines (at least the FWD versions), if you filled the sump (which is 7.5-8 quarts) to the full level cold, and you went to measure it hot, you'd be "overfilled" by about half a quart. Folks would complain about excessive oil usage because they kept topping the oil off cold. When recommended to keep the oil at the full line, WHEN HOT, oil usage would suddenly not be there anymore. Full when hot is typically about half a quart "low" when cold.

As noted above, it just depends on how the dipstick is calibrated. I'm sure larger volume sumps experience this effect more, due to the extra volume of oil that does expand.

 

[HyperJinx]

Well today I just had to investigate this issue using my Vette (which is the same as the OP's Vette). I checked the dipstick after sitting overnight and dead cold- the dipstick read exactly full. I drove the car 26 miles and returned home, turned the car off and waited exactly 6min to check the oil. The dipstick read about 8oz low or just a hair below the full "dot". I waited another 5 min which would make it a total of 11min sitting and the dipstick read the same (just a hair below the full dot). I returned 1hr later and the dipstick read exactly full.

 

[HTSS_TR]

I check oil level, tire pressure ... in the morning when they are dead cold.

 

[sangyup81]

Do both!

 

[Jim Allen]

Originally Posted By: sangyup81
Do both!


Agree! Check it the way the manual specifies, then again in the opposite situation to see what the level looks like. Then you know and you can check it in any temp for an accurate reading. If the manual does not specify (it's been a while since I had something that did not) I would also check it both ways and compare the results. I suppose in that circumstance, I would tend to adopt the warm level (hot but allowed to drain down for 10 minutes or so) as a base standard but I would probably look at the overall situation before deciding.

 

[mechtech2]

ledslinger has a good point. Some oddball systems may need a specific window of time because of extra oil lines, coolers, etc..
Poor anti drainback devices.
Still, a good overnight cold check is the most consistent. Just realize where it should be reading - a bit higher on the dipstick.
All you have to do is check it 'their' way, adn then cold.
Now you know.

 

[SpitfireS]

Originally Posted By: calvinnnnnnnnn
most important thing is that your car is leveled

I could not agree more.
No matter how long or short you may or may not have to wait, if the car is not level the reading will be wrong.

 

[Audi Junkie]

I take the reading cold and don't fill to the top of the range, rather leave like a 1/4 quart amount out.

 

[diver1972]

Originally Posted By: Gomer03
I've been operating my whole adult life on the principle that only a cold reading is truly accurate.


I've had a similar mindset over the past decade or so, but not sure where I got it, so I did a little test sequence on the Camry in the sig block.

Sequence:

• Run to operating temperature. Turn off.
• Check level after 2 minutes.
• Check level after 5 minutes.
• Check level after 30 minutes.
• Check level after 60 minutes.
• Check level after 90 minutes.
• Check level after 480 minutes (i.e. overnight).

Results:

Minutes since off: Level*

• 2 minutes: 2/5
• 5 minutes: 3/5
• 30 minutes: 3/5
• 60 minutes: 3/5
• 90 minutes: 4/5
• 480 minutes: 4/5

* Level = distance between L (low) and F (full) marks; I chose 5ths to give a reasonable level of granularity


Conclusions: The difference between the lowest reading and the highest reading is 2/5, or 40%, of the distance between L and F marks. Per the OM, the distance between those marks represents approximately 0.7 quart (yes, it states just that). To be more conservative and simplify the math, I bump this to 0.75 quart. This means that 40% of the 0.75 quart is about 10 oz. Per the OM, the oil capacity, with filter, is 3.8 quarts. Thus, 10 oz. is 8% of the total capacity in this application. Since the OM specifies checking at operating temperature and "a few minutes" after engine off and to give the dipstick handle a chance to to cool down some from the piping hot exhaust manifold, I think I'll adopt the approach of checking it 30 minutes after engine off and make that my new practice.

 

[Vikas]

That was a great experiment and I thank you for posting the results. My impression has been little different i.e. do not think I have noticed 40% difference between warm and overnight on my 1999 Odyssey. I do make sure it is parked in the same location. It would be interesting to see what other people have observed.

 

[uart]

Yeah good experiment diver.

I've never noticed that much difference myself, but then again I never measure it anything under about 5 mins after shutting down.

Usually I just wait 10 min and then check it. Leaving it longer, even overnight, only seems to make a fairly small difference. About 5mm from memory

 

[diver1972]

Originally Posted By: Vikas
That was a great experiment and I thank you for posting the results.

Thanks.

Originally Posted By: uart
Yeah good experiment diver.

Thanks.

Originally Posted By: uart
Usually I just wait 10 min and then check it. Leaving it longer, even overnight, only seems to make a fairly small difference. About 5mm from memory

My quick test agrees. While I didn't previously measure the differences in absolute lengths, I measured the distance between L and F on that 5S-FE dipstick; it's 20mm. So, the difference between 3/5 and 4/5 equals 4mm (more relevant) and the difference between 2/5 and 4/5 equals 8mm (much less relevant because of my "premature" 2 minute readout).

 

[gregoron]

I check cold. Oil sticks to the dipstick better. Be consistent though, when you're also adding oil.

 

[garlicbreadman]

always cold.. it measures higher as oppose to hot

 

[DragRace]

i've always checked oil when it's cold,no experiments required.

 

[armos]

I can't even read the dipstick unless it's cold. I've tried.
At least on my car, I found that being level isn't as critical as I expected. I checked oil cold on flat ground, then again in my usual parking spot, and it wasn't much different.
This is definitely something one should test on their own car though, if they need to take readings on a grade.

 

[mr_diy]

Does anyone know the expansion difference for oil cold to hot?

I imagine to main difference for Toyota (side mounted filter) is if the oil filter anti-drain-back is holding oil back over the cool down period. It is also possible the oil pickup to filter passage, over enough time, may drain back. So hot checking may just take these variables out. Oil level going down (Northstar) as it cools doesn't make sense unless hot oil expansion is a significant percentage.

Maybe it is worth testing the hot/cold levels with old/new and different brand filters to assess ADBV performance.

 

[Spector]

In my experience oil actually does expand a little when hot and I always get a higher reading after 30 min or so after shutdown then the next morning when oil has cooled off. Just my opinion but a cold reading to me is more accurate

 

[Spector]

Of course then there is the manufacturer who says 5 quarts which brings the level to halfway between the full and add mark, the dealer says they add 5.3 quarts at oil changes but to actually bring the level to the full mark it takes 5 1/2 quarts. Dealer says Ford is aware of the issue but the owner's manual does not change, still says 5 quarts.

 

[FZ1]

Cold.