dfinnegan

I've been curious for some time about how much the oil in our cars expands when it gets hot and decided to do a bit of research.

I've turned up a reference that states that Volumetric Thermal Expansion is described as dV = beta V0 dT.

In english that means that the change in volume (dV) is equal to a coefficient (beta; varies by substance) multiplied by the starting volume (V0) and also multiplied by the change in temperature (dT).

Another reference indicates that the volumetric expansion coefficient for unused motor oil is 0.00070 (1/K). The (1/K) indicates that it should be used with Kelvin temperatures; which is similar to Celcius.

So, for a 60 degree change in temperature (30C->90C; 86F->194F) the change in volume of a 12 quart sample of motor oil would be 0.0007 * 60 * 12 = 0.50 qt.

Half a quart.

Bottom line, our engines change oil level by roughly half a quart from cold to hot.

Indycam

Cool !

Wachuko

Pretty cool... but check your math. Should equal 0.504 not 0.05 . Does not change your finding.

Computamedic

It's an interesting calculation but I would have expected a much larger change in temperature to use for the calculation. Given an even ambitious ambient temperature of 20 deg C (for the UK anyway), a really hot engine is going to get oil up to around 120 deg C I would have thought, in which case the dT is more like 100 rather than 60. That relates to a dV of some 0.84 of a quart. This very effectively emphasises how important it is to NOT top up the oil to the max unless the engine is REALLY hot.

Thanks for the math lesson, Dave - it makes a really useful point.

Regards

Dave

elbeee964

Cool.

I'd wager that the factory's put in safety margin from catastrophic results, oil-wise, (say, either oil starvation, or oil spill-over-into-intake) for all combos of HOT & cold, FULL & low.
No big concerns around my garage...

This, I'd chalk up to one of those cool factoids associated w/ hauling around 12 qts to make slippery a 6 cyl. engine.

dfinnegan

Thanks, Jaime. I've updated the post. I had it correctly in my notes, then double checked my post. I've also ordered two more quarts of ATE 200 as I let my reservoir run low on the last bleed! I could use the practice.

Rob in Oz

"The (1/K) indicates that it should be used with Kelvin temperatures; which is similar to Celcius."

Just FYI and it doesn't affect the calculation result, 0deg C = 273deg Kelvin, 20deg C=293deg Kelvin, 100deg C=373deg Kelvin. ie deg Kelvin = deg C + 273.
Just another nerdy fact for 964 owners...

Rob

frank964

G'day
I'm new on this Rennlist.
It would be interesting to see the volumetric difference between filling the fuel tank from a cold winter to a hot summer. I'm sure there would be a difference in the mass of the fuel.... but not the price....?

crg53

The tanks are deep in the ground, so that the temp stays pretty much the same over the seasons, close enough that the affect on volume would be insignificant.

BlueHeeler

+1

If you fill up a motorcycle in summer you can feel through leathers the tank gets cold, which is nice.