Yeah, I know ! I read this already weeks ago on this site. That's when I was preparing my mods. Nice stories.
I can get some more black plastic undercover of a car that's going to be thrown away. I will stick with that I think, and maybe even make a sumpcover for my wife's little car.
If somebody's interested: today I filled up my Civic's fuel tank! First time after mounting grill block =>
EXACTELY the same fuelconsumption as the time before (6,07 l/100 km), also boardcomputer showed exactely the same as previous time: 5,6 l/100 km.
After all, I'm not unhappy with this result given the circumstances (compared to my previous fill up 3 weeks ago):
- very stormy wheater
- a lot of rain and water on the roads
- always headlights on (morning and evening) and wipers
- grill block only 1/3 of tank on it
- winterpetrol gives less energy/liter
- 80 km after mounting grill block BC showed -0,1 l/100km for average consumption of this tank
More news next time !

if you can keep summer mileage through the winter, you are doing good.

BTW, I really like your car. the back doors look similar to the chevrolet spark that should be coming to the states next model year. I wish honda would bring that style car to the US.

Love it! That's how I got wiring for my stereo. The store had irregular lengths for sale for pennies on the dollar.

It's amazing what you can get if you just ask - and keep your eyes and ears open.

Keep us posted, your research is very interesting.

You can count on it, I will post my findings for some coming fuel tanks. I'm lucky I don't drive a lot, so 1st complete tank with grill block is still 'going on'.
Situation after approx. 65% of this tank: BC is on 5,6 l/100 km and that is according to me a success as temperatures are low (for Belgium...that means right now just freezing -1 to -5?C).
As Beef already said: I should consider this mod successful if I can keep a steady fuel consumption in winter.
Because of the freezing temps I now have the grill covered for approx. 95%.
I'm monitoring the temps very carefully with a diagnostic tool and in this wheater there's no risk for overheating. The cab heating on its own is taking all the exessive heat of the engine. Radiator temps hardly reach 25?C when freezing and the engine reaching its normal 85?C takes almost the full 30 minutes commute. Oil doesn't reach its normal 85?C. I've noticed the oil has a real cooling function: from the moment on the oil does reach its 85?C the cooling capacity is unsufficient when blocking 90 or 95%. But as said: no risk for this when freezing. With the diagnostic tool in the car I take no risk and can experiment 'unlimited'.

My '04 Dodge Dakota 4.7L V8 used to overheat because of a bad aftermarket thrermostat. I would just crank the heater up and roll the windows down to cool the engine off quickly.

I suggest cracking a window on the passenger side to give the heat a place to go. :thumbup:

Block grille too much and use heater and open window to vent extra heat seems like a pointless procedure, now you're still getting rid of the same heat and you've got the aerodynamic disadvantage of an open window instead of an open grille.

I know man,
I will remove (a part off) grill block the moment on my engine can't get rid of its heat on a normal way.
As it is now I never had to open a window and I only had to turn up cab heating one time to cool the engine (with closed windows, it's winter and a few degrees more in the car don't hurt).
Thanks for your care and tips!

Brings back memories of a day years ago, in a 1962 Rambler American (basically a 1939 Nash with a more modern body) midsummer, about 105 degrees, on the Ventura Freeway in LA, puttin' along at about 2 MPH (there was a chemical spill, and traffic was backed up for miles and miles) and I sat there, watching the temp gauge creep up and up (belt-driven fan, turning slowly), finally had all the windows down and the heater at full blast...sweat so much I lost about 10 lbs!

Back to subject at hand...I am trying a 1/2 grille block on the Geo...so far haven't noticed much gain (in fact, my MPG has actually dropped, but I think it is because I have been driving faster lately...)

Unlucky wheater conditions yesterday and today.
Now the freezing temps are no longer alone. Snow accompanied them. And believe me: not a bit!! Exceptional wheater in Europe (Belgium, France, the Netherlands, Germany...). Took me one way 15 minutes longer to go to work + very slippery roads with loads of snow + slipping wheels + windowdefrosting + aerodynamic advantage of grill block doesn't play at these low speeds.
So my fuel consumption increased first time with grill block: BC shows now 5,7 l/100 km (was already a long time 5,6). This is less than 2% increase. Tank isn't emptied yet, but the weather forecast is clear: this weahter continues the coming days. I read on European Civic forums that fuel consumption in winter can increase from 10 to 20%. So my 2% doesn't look bad.
It's a pity I can not compare the car's fuel consumption with last years winter as I drive her only since mid September.