Hot or Cold Oil

One of the most important conditions for any healthy hydraulic system must surely be temperature.
The number of times I have examined power-packs where you could easily fry an egg on the lid. I once heard a story (not sure how true) where a hydraulic engineer was asked to examine a very noisy system. He found that the RL filter was covered in paper labels from operators who had lowered their tins beans into the tank to warm them up for lunch. The paper labels would gently float off the can and end up on the filter.
Obviously this must have been a system that ran far too hot plus a dose of cavitation to boot.
Heat can also cause more long term problems including the breakdown of the hydraulic oil. Additives protect the components, the change in viscosity will cause increased leakage (slower speed) and seals will become brittle.
Ninety percent of the time, I find a hot systems will be down to a relief valve blowing. This creates wasted energy and is immediately converted into heat.
Cold oil is also a problem. Some systems will not work properly until they reach 20-30 degrees Centigrade. You might think that this does not cause any long term problems but cold oil can often mean thick oil and thick oil can cause cavitation (another pump killer)
It is very important to design hydraulic systems that will operate at the correct temperature and if possible without the need for special cooling.
Most of the hot systems I see are often just shear bad design or built for very low cost.
This is a very wide subject and I would love to hear about yours views and experiences.
Cheers
Bob