My car is a Seat Leon 1.9 tdi BXE 77kW (spanish VW Golf) you could see in the attached frontal view pictures the differences between a cd=0.325 gray 2006 version 5.2L/100km (EU averaged), and 0.30 2010 ecomotive (3.8L/100km).
My first tray has been blocking my upper front grill with tape because Seat uses a plastic one in a car with +37% mileage (-27% L/100km) than mine, and second because the Racing version of Seat Motorsport and other preparations use a different full blocked, partial blocked upper part of upper grill, full upper blocked but with a direct hole to airintake... all of them are PEtrol engines from 200 to 300 bhp, or diesel above 250 bhp. Mine with 105 bhp, maybe doesn't need higher air cooling on my radiator, front intercooler and A/C condenser than Racing Seat Leons producing 2 or 4 times the heat.
I will buy the upper grill made of plastic at Seat Dealer, but first I must to solve a little thermostat issue (that opens near 80ºC, and not 87ºC) that it seems very common on VAG engines. I discover it because of large data logging using OBDII port (with Vag-com 311.2, because is not needed CAN-BUS VCDS if you only want engine module be accessed).
I did some accurate runs at 18ºC and 23ºC (influence temp. difference below 1%), at 82-94-122 km/h, and because of overcooling my fuel consumption have a 4% increase (-3.9% MPG).
This first aerodynamic success of -5% drag has motivated me on going to 0.30 or even better. To improve my fuel consumption expected -5.2% on average. When my thermostat and aeromods will be adjusted i'm waiting for a -10% fuel consumption. From 6.7L/100km to 6.03L/100km, that is 35.1 to 39.0 us mpg.
If i did these mods with Seat original german design parts it will cost around 93€ (closed black grill+central spoiler+thermostat+G12 refrigerant). I will post my numbers then.
My actual numbers, open grill ->tape closed grill:
82 km/h: 4.36 -> 4.23 L/100km ; 53.9 -> 55.6 us mpg at 51 mph
94 km/h: 4.73 -> 4.57 L/100km ; 49.8 -> 51.5 us mpg at 58.4 mph
122 km/h: 6.67 -> 6.42 L/100km ; 35.3 -> 36.6 us mpg at 75.8 mph
Also I realized this morning that my TDI cam timing is -2.5 to -2.0, so my cam timing must be changed because is delayed. When the volkswagen plants makes the engine the cam timing is set now between -2.5 to 2.5 on PD engines (rotary iinjection pump range was -5 to 5) this margin is caused of visual accuracy on mounting. A perfect timing will need some trial and error occupying valuable minutes-man in the factory line. Better setting must be 0.0 to 1.0, but foud in several discussions in forums like
Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community they say better cam timing is advanced one in the range 2.0 to 5.0. I have a 1.9 TDI 110 cv AHF with the timing at 5.0 set at the Dealer when changed the timing belt, and If i can i would swap this two engines altought mine has 58.000 mi, and the AHF engine 190.000mi. I'm going to set this and accurate measure the changes in fuel consumption.
I didn't expect my on road accurate measuring based on OBDII (wind and forecast also,...) will make me tuning the engine first,
