Can you mix cold and warm oil together? If no, why is it so?


Me and my coworker had a conversation about mixing the same type of oil (Hydraulic Oil; hlp mineral oil) together, but with different temperatures. Is the warm oil “swimming” on top of the cold oil? Or are they mixing?

In: Physics

They should mix. Polar molecules mix with polar ones and nonpolar ones mix with nonpolar ones. Both oils should be nonpolar, so they should mix. Their temperature difference should then quickly cancel out as well, though it might be some of oil A might stay on top (but mixed) if it’s hotter or has a lower density.

There is a differences between pouring oils of even water of different temperature in a container in a relative car full way compared to physically mixing them by stirring the liquid.

If a Hydraulic Oil reservoir where the return flow is on top there might not be a lot of mixing and the warmer oil will have lower density and stay on top.

You can do the same experiment with water. Put cold water in the bottom of a glas and pour warm water ontop carefully along the wall of the glass. They will mix a lot less then you would expect. Use food coloring and you can do experiment like [](

The water temperature effect can be quite clear if you swim in water outset. If the water is relative still and is relative cold the sunlight can heat up the surface layer so there is a clear diffrenc so your feet can feel to cold on the bottom but close to the surface the water has a present temperate.

The surface water can be a lot warmer the the water below and there can even be situation where warm water is trapped below cold water.

So they will mix but it can be a lot slower then then you suspect if there is not stirring.