how much does oil expand when heated?

[The motor guy]

So I notice a lot of reservoirs seem to not hold much fluid. The hydraulic reservoir on my mower only holds about 1/2" of fluid at the bottom of a 7" tall reservoir, my power steering reservoir seems to be the same way along with my transmission pan. How much does oil expand when it heats up?

 

[lubricatosaurus]

About 4% more volume per 100 degrees F you heat the oil.
http://www.engineeringtoolbox.com/cubical-expansion-coefficients-d_1262.html

So, from room temperature to about 210 degrees F is 140, so oil expands about 6%.