Yes, I remember one of the first things I learned when I started my engineering training was that there was more variation between any one company's consumer petroleum products summer and winter formulations than there was between different companies' products for any one season.
While I don't doubt the mechanism, does the relatively small volume of warm/hot diesel returned to a tank full of cold fuel make that much difference- especially as tanks tend to be under the vehicle and exposed to the elements (at least on the vehicles I've seen).
That takes me back to some tank trials I was involved with in a very cold Michigan winter. The tank had been fuel with 'summer' diesel and the onboard heater (which was diesel fueled) 'waxed up' (the engine seemed to cope). I can describe how cold it was in that tank without using language I don't use normally!
Brian Reay pretended :
It must, why else would manufacturers go to the expense of adding a fuel cooler and thermostat. The stat diverts fuel either direct back to the plastic fuel tank, or through a small radiator to reduce its temperature down to an acceptable level.
Feel the temperature of your HP pipes from HP pump, to the injectors - they will be quite hot due to the very high pressure created by the HP pump. Surplus hot fuel, not used by the injectors to squirt into the engine, is leaked back to the tank. Hot enough to melt your plastic tank.
the fuel in the tank does get surprisingly warm, it is not just the spill pipes feeding it, there is constant significant flow going back to the tank.
Far enough. You learn something everyday.
MrCheerful used his keyboard to write :
The less the fuel level and longer you drive, the hotter the contents will become, without some means of cooling it.
BMW have had to recall a load of 3 and 5 series due to faults in the fuel cooler. Mine was caught fairly early, before it caused any issues - but a colleague who also has a last shape 520d had a minor engine bay fire caused by a fractured fuel cooler.
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