After reading a bunch of the lunatic ramblings of others here about how well grille blocks work, I've decided to dive into the experimentation myself.
So far I haven't done any efficiency testing, but I've completed an ABS block-off that completely covers the upper grille opening. I'm not really concerned about overheating until temperatures climb near the 80 degree mark, and a couple of short drives in 60 degree weather today confirm that it's likely not going to be an issue even then unless we are towing or climbing allot.
I think it actually looks fairly decent too. I'll post some pictures tommorrow and will hopefully be able to report some highway results.
If nothing else, perhaps the interior of the truck will simply heat up faster on cold days.
The blockoff is 1/8" ABS. The stuff is really durable and easy to work with, plus it's the same material that other textured plastics, such as the mirror housings and bedcaps, are made of.
Preliminary testing this afternoon is a bit inconclusive, but hints at an improvement.
Over a 20 mile loop run back to back at 60 MPH with the cruise control set, first with the blockoff, then without, the end result was 22.1 mpg vs. 21.9 mpg as indicated by the in-dash display. Better more than less I suppose.
Broken down a bit further:
leg 1, 22.5 MPG
leg 2, 21.7 MPG
leg 1, 21.8 MPG
leg 2, 22.0 MPG
The truck was fully warmed up before testing, and ambient temperature was 62F with dry roads, no lights or AC. The only real variables were traffic and filtered sunlight. I believe I was able to avoid any draft advantage by going 5 mph under the speed limit, limiting the amount of time other merging vehicles spent in front of me.
Unfortunately I didn't have time to repeat the tests to better define the margin of error, but I'm liking the 0.7 mpg difference that the leg 1 results suggest. If the leg 2 results are the worst of my margin for error, that 0.7 mpg is a 3.68% improvement. Obviously if the best case is reflected by the overall average, it's a mere .91% improvement.
And yes, I'm surprised that our truck will actually get nearly 22 mpg at all. It seems with normal daily driving, trying to go with the flow rarely yields much more than 18 mpg. on the highway.
I just filled the tank today as well after the testing, so I'll attempt to track the tank average, although that will likely involve about 75% city driving.
Snax, did you also block off the openings in the bumper, below the grill. In order to get the benefit, I believe those need to be blocked off, also. In any case, on mine I blocked those off, as well and then added some holes, to keep the temperatures at normal, as necessary.
I wonder if it might make a difference how much clearance their is under a vehicle, on how much of an affect the grill block will have. It seems like under a F150 their is so much volume of space, that maybe it makes a less noticeable difference than on something lower to the ground?
I haven't worked with the lower opening yet. That may be phase two, however after looking under the truck yesterday, I think that is the area with the most potential for improvement. Unlike most unibody cars, the suspension and subframe bracings drop a good 6" below the bumper valence and are a good source of turbulence. An undertray set just for the front half of the vehicle would clean up the airflow quite allot there. I'm not sure how serious I want to get about working around the exhaust system toward the rear however.
I think that either a brush guard style front undertray, or a flat front undertray attached to an air dam would provide a similar result, with the former forcing air vortecies toward the side sills, vs. air spilling back under behind the front wheels. I doubt that issue makes much difference except perhaps how the airflow works around the rear wheels.
Here's a photo of the grill block on my 97 F150 4X4. Its just black duct tape and if I run into any overheating problems when towing, etc., I can simply remove some the tape to increase the cooling flow (and replace it after I disconnect the trailer).
Where did you get the ABS from, how much did you get, and how much was it?
Sorry for all the questions in my first post.
I've been looking into getting a sheet of ABS for a belly pan for quite sometime but can't get past the initial cost of the plastic. I like the factory look of the ABS and the ability to withstand more abuse. But again, it comes at a price.
How did you fasten the blocks to the grill? Is it just a simple nut and bolt setup with oversized washers?
Has anyone ever thought of using a large sheet of clear plastic film to cover the entire front end of the car? That would cover all the openings, its quick, and keeps the stock look.