Conducted a mileage test today with the 4 under body covers removed, engine cover still in place. I ran a baseline test with the covers on, removed the 4 under body covers, and reran the test under the same conditions. The engine cover remained in place. I was careful to check tire pressures 48 psi, ambient temperature 58 degrees, wind none, windows all up, climate control off, same tank of gas. Used the same stretch of freeway 8 miles West, then 8 miles East, then repeat. 32 miles total with covers on, then another 32 miles with them off. Used cruise control for entire test both ways each time, speed 70 MPH. Terrain is a bit hilly so mileage isn't to good but my results were consistent. Results 45.8 MPG covers on; 45.7 covers off. Essentially no difference, I was actually surprised the numbers came out as close as they did. I had the covers off looking for rattles and decided it would be interesting to test the mileage. I think they must improve the CD number a little or we wouldn't have them, but in the real world they don't seem to improve the mileage. I am going to put some sound isolation under them and reinstall them. They might actually provide some protection for cables, brake and gas lines, etc.
Tumbleweed, Thanks for the information. Installing a sound deadening material under the car is a great idea. I know road noise is a little high in the 2010 and that may help. I may do that myself.
I haven't found a product yet, I was hoping for some suggestions. They will get wet when it rains and will need to be kind of tough because the covers had quite a few rocks in them when I removed them. I'm going to check out the local hardware store and the modifications threads on here first.
I know local customization shops sell a "sound insulation spray on" stuff but it's expensive. I'm subscribing to this thread, so I can see what you use, and how well it works!! -Brad
Thanks Brad, I'll try to find some of the spray it might be what I need. I was going to try some foam rubber stuff that they sell for upholster work but I'm afraid it would suck up water like a sponge, which is what it is.
How about "Great Stuff Insulating Foam Sealant". You can find in just about any hardware store. I would suggest the minimal expansion type. I'm not sure how much clearance you have.
There is 2 or 3 inches between the covers and the car when they are installed. They have plastic spacers, except the front and back couple of inches of each cover which touch the car. I may end up using some kind of fiber glass blanket or something such as that. I looked all through Home Depot and Lowe's today, didn't find anything I liked. I am a little reluctant to use the spray Brad mentioned or the foam insulation because I think once it drys it doesn't come off very well. If I make a mistake and put it in the wrong place it would be hard to recover. I might try a little bit as a test though, I think I have a can of foam insulation out in my shop.
Thanks to everyone who replied. This thread by Gwest in the Audio forum, who has done some great stuff to his Prius, contains links to some good (but expensive) products that I might try: http://priuschat.com/forums/gen-iii...90-noise-control-sound-vibration-damping.html Two of the suppliers he mentioned are: Soundproofing & Noise Control Materiels Prices Car Gasketing Foam for soundproofing cars
Tumbleweed .... most interesting. I will bookmark this thread and follow the replies. I wish I had a brand name for you, but I recently visited a high end home under construction, and the contractor was installing a sound deadning material on select walls (bedrooms, play rooms, bathrooms) behind the gypsum board. It was about 1/4 inch thick, flexible,and black in color. The contractor implied it was a new material, and was very effective.
Try a product called Dynamat. I have used it inside a 55 jaguar under carpets. I have seen people use it under the car. It is a foil product backed with some sort of a thick , black adhesive. It should be weatherproof. I don't have a Prius (yet)...but am selling/trading a 2007 4 runner . I was just researching the subject of underbody covers and seeing if there was any protection if my wife visits horse farms and unpaved roads.
The thing is that it is likely that there aren't many changes that make a huge difference. Most will be small things like this. Car engineers talk about 'counts' which are (I think) 1/100 of a point of CD. A thousand small changes add up to a large change.
I had, until the engine expired, driven for 5 weeks with no wheel covers on. 60.8 mpg. But I don’t go on the highway, max speed about 40 mph.
