Mileage Test With Under Body Covers Removed

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.

 

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.

 

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.

 

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

 

That could be OK, sounds like a trip to the lumber yard might be in order.