About 2 weeks ago we had a heat wave here, so I removed the upper grille block (ver 2.0). In warmer weather, with the upper grille blocked, the engine would warm up faster, even out around 78-80°C, and stay there until I hit a small climb or stop&go traffic. Then the temperature would rise to 90°C and slowly inch upwards, even if I'm peacefully P&Ging again. The temp would climb to 97°C, then quickly fall to 89°C (fan kicks in at lowest speed), then again and again. It's almost impossible to keep the temperature stable, opening the lower grille block only slightly extends the cycle.
With the upper grille unblocked, the coolant temperature hardly ever goes above 80°C, even with the lower grille closed.
So why am I complaining? Because I get better FE with a hotter engine. Example: Trip #1: 60km through the city, had luck with the lights, but lots of overpasses, outdoor temp 28°C, upper grille blocked, coolant temp at least 90°C, consumption 3.2 l/100km.
Trip #2: 40km on the city's edge, Sunday 8am, taking it slow, no overpasses and 2-3 lights, outdoor temp 8°C, upper grille open, coolant temp no more than 78°C, consumption 3.7 l/100km.
The above implies that even if the fan keeps turning on, then I still get much lower FC with a warmer engine. I admit that this is by no means a good A-B-A-B test, since the routes were totally different. Trip #2's route allowed better hypermiling, but the hot weather on Trip #1 probably resulted in faster engine warm up and lower friction in the bearings.
Unfortunately PSA doesn't make a hotter thermostat for my engine, and the one it does make is wrapped up with some sensors in a plastic housing, so no way to
hack it like in a TDI. I could make an openable upper grille block, but that would be overkill: the lower grille already has
two independently openable blocks.
Any ideas? Maybe a partial block for the summer?