Grille block success
 

I recently blocked the area below the front bumper and above the chin spoiler (if you can call it that) with round foam pipe insulation. After 2 tanks it seems to have made a significant difference in economy. No official tests, but the last trip i did looks to be 44 MPG at 20 deg F, which is quite a bit higher than the 38-41 MPG I usually see in the winter. It also warms up nearly a mile quicker from a 10 deg F startup. I think the front bumper, which sticks out far (on this old design) previously trapped the air deflected up by the chin spoiler, funneling loads of freezing air into the engine. I think a lot of gas can be saved by really sealing up the front in really cold temps! (just make sure your engine is running at the right temp, and you havent covered an important trans cooler or something).

I haven't experienced any noticeable difference with my grille block added. Granted it's not 100% air sealed. I have mine blocking the interior opening of the bumper. Perhaps it would be more effective if it was flush with the exterior?

I'm guessing it would perform better out in front. Of course if your average speed is 20mph, aerodynamics wont help so much.

I have a 98 with a lot more texture to the front bumper, I may try to fill it in with urethane foam or something and cover it in monocote :) (sorry, RC sailplane hobby coming through)

I think that by blocking the exterior the aerodynamics would be significantly improved. I used clear tape to tape many of the cracks for the front grille, except a small 1/2 in.x10 in. for intake, including the cracks around headlights, etc. The clear tape lasts longer than you would think if you clean the surface first and put it on right, lasts about 6 months, and easily pays for it self several times.

Hmm, I'm thinking it's about time to put my bumper back on... :p

While I think aerodynamically it helps I bet most of the gain is from the engine warming up faster. I used black "gaff" tape, similar to duct tape except it can be removed without leave a gooey residue. It makes a huge difference. My upper grill just a piece of plastic behind the grill, I like the "stealth" look.

Heck even last night running home I only hit 164F (73C) and I don't turn the heater on until it hits 140F (60C), but it was windy and 11F (-11C) outside

https://www.uwgb.edu/nevermab/tdi/grill.jpg

yeah that looks slick on the tdi, i like it, my clear packing tape on the front grille is ugly, but then again i drive an 89 camry, and i live on a dirt road, so my car is plastered with mud half the year anyway.

Where do you get "gaff" tape? Will Wal-mart/Lowes/Home depot carry it? My chloroplast block is taking forever to fit snug in the crevices of my lower grill on the '85 Si and tape is a decent bandaid til then. Thanks, Mak

I almost forgot, I did a grille block too (till I got a funny look from a golf driver today). Started with "great stuff", used light spackle after that and some bondo in spots. I considered using the kids play-dough and mud/sticks.
It still needs work, but good enough for now.

Here's the air hungry grill that is backed up by a solid wall mostly:
https://www.gassavers.org/attachment....1&d=1169774379


And here's the quick and dirty block job:
https://www.gassavers.org/attachment....1&d=1169774379

I am not sure where to commonly get gaff tape. I work in a theatre and we use it here and I bought two rolls from the theatre when the theatre bought a case. I would think any theatrical supply place or maybe even musicians supply place if they have band gear as well. I didn't look on eBay, but they seem to have everything else ;) It is $12 a roll when I bought it so it's pricy.

I honestly thought it might not hold up being on the front in winter, with the salt and car washing and all, so far so good.