Grill Blocking Summary Article

The Prius’s small aluminum block internal combustion engine tends to lose heat very quickly. During the first 5 to 20 minutes (depending on ambient temperature), the car’s mileage will take a hit due to the high heat loss. Several PriusChat posters have been able to suggest and prove a valuable tip for retaining this heat better and preventing the engine from cooling to quickly. This tip is to block either or both of the upper and lower grills on the Prius. The purpose of this article is to provide an overview of some of the more notable or valuable PriusChat postings on the subject.

There have been a couple of very good threads on PriusChat about grill blocking. The "original" thread that discusses this topic was one started in December 2006 by Tony Schaefer entitled First Morning with a Blocked Grill. There are discussions within the thread regarding the reasons for blocking a grill, the benefits of doing so, warnings about temperature extremes and directions for doing the "grill blocking" yourself. Along with these directions you'll find pictures of the end result for a few different ways of accomplishing the task. There is even a graph showing one poster's claim that the grill blocking has resulted in a 4% increase in MPG even with a very short commute.

A quick observation of note: PriusChat Member usbseawolf2000 records the same observation I have noted: The grill blocking, particularly the blocking of both the top and bottom grills, will cause the car’s thermometer to mis-represent the outside tempature . This difference will vary depending on the installation and how much of the grill has been blocked, but the number showing up on the MFD screen is likely to be as much as 3 or 4 degrees higher than the ambient outside temparater.

Here are some example photographs (and a video) from the thread:

1. The basic pipe insulation used by Fire Engineer (Wayne) and Tony Schaefer.
2. A view of the compression-fit insulation pulled back from the grill -- to show how to install (insert) the insulation in the grill.
3. A photo of the Doc's (Efusco's) version of grill blocking. This one uses a different type of pipe insulation, and also has a more complete cover of the grill. Efusco's version uses the full diameter of the pipe insulation. The whole piece covers the grill and is held in place with zip ties.
4. Another installation like Efusco's, only this time the pipe insulation is held in place with the adhesive that comes on the material. This is a clean look with no zip ties. The poster (usbseawolf2000) also includes a [ame="http://video.google.com/videoplay?docid=-4774360504510051993"]link to a video[/ame] of his installation. Efusco offers a warning that the adhesive will leave a residue that proves difficult to remove from the grill and/or bumper.
5. Hobbit's version (or at least a link to it) in which the blocking is behind the front grill.
6. Another modification of the style shown earlier by Efusco. This one uses zip ties on the top grill just like Efusco, but on Boo Gas the bottom grill's zip ties are set up so that the pipe insulation can be adjusted to allow more or less air flow. The look on the bottom grill is more like a quilted blanket (IMHO).
7. The Combo Method: This one uses a compression fit on the upper grill and the full-cover, zip-tied method for the lower grill. This poster started with the pipe insulation used by Tony Schaefer but switched to the pipe insulation used for covering air conditioning pipes. This other insulation is a different type of foam that is more flexible at lower temperatures. It also is a bit darker in color and has a smoother finish. It also was used by Efusco.
8. The "Cut-to-Fit" look -- In this one the poster ("JimN") cut the pipe insulation into 8 separate pieces for the upper grill. This gives a very clean look.
9. The latest look. Whereas JimN got a very clean look by cutting pieces to fit, I just cut the pipe insulation to fit (tightly) lengthwise. By using the foam for air conditioners (darker and without the open cells showing) and cutting it down to narrow pieces fit to the whole length of the grill, I think the effect is to make the foam nearly disappear. This is my attempt to get it done after reading through the past year's worth of postings.

More Information on the Pipe Insulation Used: Posters have offered differing opinions on the appropriate or “correct” size of the insulation to be used for blocking. I offer the following observations based on my experience:

1. I prefer the darker pipe insulation, because it is more similar to the color of the grill and, therefore, tends to “disappear” more easily into the grill.
2. I prefer the pipe insulation intended for use with air conditioners. This insulation should hold up better at lower temperatures, and it will retain flexibility better than the less expensive foams. I have purchased it in 6’ lengths.
3. The thickness of the foam should not exceed 1/2”. The other option in size is the intended width of the pipe to be covered. I don’t believe you need to exceed insulation intended for anything larger than ½” diameter. This sized piece can be cut in half length-wise. The portion of the foam containing the adhesive can be trimmed off, and then the two long pieces may be cut in half. Each of these four quarters can be placed in to the bottom grill without any additional cutting.
4. The best way to insert the foam is to center it in the grill, place the lower edge into the grill opening first, then while forcing the foam to be folded in half, push the top part of the foam piece into place. This completes the “compression” fit and will allow the pipe insulation to stay in place for a long time.

I hope this helps you navigate a very long thread with LOTS of valuable information.

I don't want to discount other, valuable threads. I just happened to have relied on the one noted above. Here are other threads to read:

1. Blocking the grill
2. My attempt at grill blocking This thread shows a VERY CLEAN installation of the pipe insulation. The poster refers to it as an "OEM" look -- and I see why. This is what I was looking to get, but I don't think I had the time and patience to accomplish this great look.
3. Quick grill blocking question
4. Sorry if this is stupid . . . but what is grill block? This is a newer, shorter thread that re-directs the reader, but offers some comments as well.

Much of this information has been summarized in a Grille Blocking page in the User Guide established by John1701a. John is likely to keep this information updated.

a priori

 

<div class='quotetop'>QUOTE(billsrule7 @ Nov 21 2007, 08:19 AM) [snapback]542365[/snapback]</div>

Try them now...sorry about that.

 

Hey guys...I have some key info I think is important for those blocking their grill.

I recently converted from my old style of block (one piece of insulation for the top grill and one for the bottom) to blocking each individual slat for a nicer appearance. I drove today from my home to St. Louis. Temps were around 42F and the terrain is hilly..steep in areas but nothing dramatic by Ozarks standards. This is all interstate with a70mph speed limit...and that's what I had the CC set at.

Previously I've driven this in similar conditions with grill blocking and temps for MG2 and the ICE were fine. Today, however, I got a little concerned. I actually witnessed MG2 temps climb slowly during the drive up to 114F sustained and ICE temps up to 204F spikes, but sustained closer to 197F.

I think the individual slat blocking gives a much more complete obstruction to air flow...great thing for short, low ICE used (aka city) trips, not so great with high speed hill climbing continuous ICE trips. If temps had been closer to 50F without ability to monitor I'm seriously concerned I could have been in the danger zone for the temps.

I stopped for gas with the intention of removing a block from one lower slat but actually forgot. When pulling out of the parking lot I remembered and stopped, backed up a few feet (25' max)...saw MG2 spike to 152F briefly!!! That's,by far, the highest I've ever seen it. I pulled the middle insulation strip for the lower slats and took off. MG2 temp quickly dropped and was down to 120 by the time I was off the exit and within a mile was below 110.

From that point on ICE temps ranged b/w 182F and188F(trending lower), MG2 was in the 70s and 80s the rest of the trip. Actually those are cooler than I would have liked, but I didn't want to stop again. And I didn't want to risk higher temps.

So, if you have your grill completely blocked with the individual slat technique and do NOT have a way to monitor temps be very very careful on highway/high speed/high demand driving conditions esp. if OAT is over40F...I used to say 50F was safe, but I would not reconsider under slightly more extreme conditions.