Diesel fuel temp / viscosity

:confused: Lately the weather has been extreamly hot, and I've noticed that with my late model vehicle 1,3 Common rail turbo diesel I have lack off performance soo I did a bit off researching and found out that in heavy traffic jams at ambient temp between 29-38 celsuis, the diesel fuel flowing in the tubing line to engine reached a max off 85 celsuis. I was told that when Diesel fuel heats up the viscocity off the diesel fuel will indeed decrease therefore my vehicle performance will be effected cause the flow efficiency reduces or increased no idea at all ????

Does anyone have any idea off what the max Diesel fuel temp in the tubing should reach or be ??? (I know that in a common rail the injector tips reach about 300 Celsuis)
Does the viscocity of Diesel fuel change prior to heat ???
Lastly how do I avoid the fuel from heating within the system fuel line???