Does oil Expand?

[ian]

My daughter has a Holden Cruze and has been having a problem with Holden over excessive oil use 3 litres in 5,000KM
they are doing an oil consumption test and told her to check the oil every week and if the low oil light comes on to bring it straight away back to them .
One dealer told her to check the oil with the engine running, to which I laughed ,on Saturday I went with her for back up the service guy checked the oil and found it had used100 mil in a week, he then told her to check the oil when the engine was hot because when the oil cools it shrinks and might give a false reading,
Now does oil really shrink that much, because I always check my oil when the engine is cold before I go any where, and would it make that much of a difference?

[Hillbilly]

You should check the oil before starting up in the morning. Always on a flat surface and preferably in the same place each day.

Being pedantic but thats the only way for the reading to be consistent.

The hot oil will drop down to the sump during the time the engine is turned off and so will have the maximum in the sump then.

Pull the stick out wipe it and then dip and read.

NEVER DIP with engine running. How stupid is that.

We used to dip our buses first thing and if we had done it running it would have been down a couple of litres with what was circulating at the time.

How do some of these people get dealer jobs??????

The reading is relative anyway As long as its done in identical conditions shrinkage wouldnt come into it.

Havent ever noticed 5 litres of hot oil not going into a 5 litre container. LOL

[Transporter]

Yes the oil expand with the temperature and the difference on the dipstick could be up to 10mm. Some oil dipsticks have 2 upper lines one for cold and one for hot.

The dipstick in Subaru engines is one of them, another example not related to late VAG cars are dipstics in the auto transmissions.

Check the oil when you get home 5 to 10 minutes after switching the engine off on the level surface.

[Abuthen]

I think Hillbilly provided the gist of the answer. Oil does not really shrink or expand with differences in temperature. The change in dipstick measurement has more to do with the oil pooling back into the sump and the metal shrinkage/expansion of the metal engine etc. Differences in temperature affect viscosity of the oil more than volumetric-wise.
Always good to check in a consistent environment, much like checking the tire pressure (which, air does shrink and expand due to temperature changes)

Having said that, oil -does- shrink/expand, but not so much that it even changes the measurement on a dipstick. For those geeky enough to want to know how much it changes, here's a calculator for that - lets you calculate changes due to temperature for water/ethanol/oil Thermal Expansion - Volumetric or Cubic

[Transporter]

More than 25 years ago I made for my mother in law the automatic glass house ventilation from the old strut (shock absorber), so when she was on holiday, I didn’t have to go there just to open the windows on it.
I’ve dismantled the strut and filled it up completely with the oil at the room temperature, then connected it to the glass house's roof windows, as the temperature raised, the strut started to open the windows and went down to close them at night.

Volumetric changes are in all directions, so the oil in the sump will rise only up, because it can’t push against the metal sump, can it? It means that the fluid trapped in the container (engine sump) will expand only in one direction.

If you want to be more scientific about it, look at the humble liquid thermometer.

The oil in today’s cars is 5W30 or even lighter in some, it flows almost like water and it will go down to the sump very quickly when you turn the engine off.

But hey, if you check the engine oil level when the engine is cold that's fine, the difference on the dipstick is not that important as long as it is above the minimum mark and up to the max. mark.

[Abuthen]

Y'all have a nice day now.