So I spent an hour making an ABS grille block for our 5. I designed it as a partial block which eliminates about 2/3 of the lower grille flow area since I didn't feel that the upper grille opening is likely sufficient in all but the coldest weather for cooling. With a triangular shape, point down, it also permits unrestricted airflow to the intake and fender cowls. But as you can assume from the title, preliminary test results are disappointing.
My test loop was a relatively short 10 miles, but that was enough to illustrate a lack of significant improvement if not reduced economy and abort more accurate testing. Road speed was 55 MPH on cruise control and 70F.:
Grille Block Test Result: 37.9 MPG
No Grille Block Result: 38.5 MPG
Considering how odd the thing looks, I'll do a cursory complete lower block test, but likely move on to other options.
P.S. I have not run a full tank through since installing the Scanguage, so the mileage figures above are uncalibrated and probably on the optimistic side.
I've got a couple of questions, if you don't mind.
Which vehicle are you doing the grill block on, the truck or the car?
When I did my grill block, I blocked the whole thing, 100% and then added opening's as the temperature gauge indicated a need. I ended up running with 2 openings about 2"*4", to get sufficient air to keep the engine at normal temperatures. I used a sheet of cardboard, which was admittedly pretty darn ugly.
In consideration of relative values, I had perhaps 5% of my grill space open. In contrast, you have about 33%, it sounds like. I am wondering if the difference your seeing isn't affected pretty substantially by the comparatively high amount of area you still have open.
Their are a couple of considerations, from my perspective. I did the test in about March. I have not run the test in the Summer. I have considered, but probably will not try to do a grill block on a trip planned across the desert, in the Summer. In all, a grill block does make a difference, but it is probably 5% or so. In contrast, I don't want to cook any of my engine, because I do not like rebuilding blown up engines.
When I grill block "too much", the radiator fan kicks on a lot and hurts economy.... the best cutoff is just enough air to cool the engine passively but not more because "more" increases drag due to the air bouncing around in the engine compartment and eventual separated air flow exiting under the car.
So block away, but look at more than just the temp gauge... the temp gauge may be fine, but like in my case, only because the fan was recirculating relatively stagnant engine compartment air through the radiator.
FYI, for all testing grille blocks... go buy a $10 electronic remote control meat thermometer.... put the thermemoter part somewhere in the engine compartment (very good for testing cold air intakes for example). Watch the remote temp in the cab.... it should be relatively steady if all is well. If it slowly increases then suddenly decreases, you probably have some fan action going on in the engine compartment.
The problem I have with it is that I can't afford to use something that stresses heat management to the ragged edge. My wife is the primary driver and I don't want her to have to think about it. I might play around with it more when we get back to late fall weather, but for now it's likely on the back burner due to other non-car related projects and activities.