Go ahead and block the upper grille, then experiment with how much the lower can be safely covered. You may make a permanent block which will be good in the summer, and a removeable section for winter.
Tip #1: Start from the sides and move towards the center.
Tip #2: Leave the IC uncovered, if possible.
You can also make a full grille block which is openable, that way it can be fully closed while the engine is warming up, then open only when needed.
Mine has two openings - one for the radiator and one for the intercooler - each controlled by a switch in the
cockpit
Re biodiesel: Peugeot allows no more than 5% BD in their HDi turbodiesels (I have the same exact lump as Euromodder, BTW), while at the same time Citroën (the other half of PSA) allows 30% in those same HDi's. Go figure
