Nissan Maxima Aerodynamic Modifications
Maxima Aerodynamics Modifications
This page chronicles the Aero modifications made to Warren's 1998 Nissan Maxima SE.
July 2008
I blocked the upper and middle grill with 1/4" foam covered in black duct tape. It is not very noticeable visibly, and even in the hottest temperatures (100 degrees plus), the car water temperature is not adversely effected. Duct tape becomes wrinkled quickly.

At the time I did not have any way to measure the mileage other than per tank. Depending on conditions, the highway mileage was between 27 and 32 MPG.

 

July 2009
I obtained a Scangauge, so now I can more accurately measure the effects of the changes I make. Also with the Scangauge I found that the car shuts off the fuel injectors when coasting (automatic transmission), but if you put the car in neutral and coast the injectors have run to keep the engine turning. This means it's more economical to leave the car in gear when coasting. Go figure... 

I'll start with the blocked grill as the starting point. This gives 29 MPG at 65 MPH on flat road and no wind. I will remove the mudflaps and rear spoiler to see if that has an effect. I have 2 sheets of 4mm Coroplast corrugated plastic which I will use next to fair the underside of the car.

November 2009
Got some aero mods done over the past several months.

  • The front air ducts are now blocked.
  • Moved the front license plate to under the bumper (in front of the big lower duct).
  • Removed the front and rear mud flaps.
  • Added a 4 ft square of Coroplast under the rear of the car. It's a start!

Driving around in-town doesn't give a great idea of any mileage changes made by these mods, so I was looking forward to driving home for the Thanksgiving holiday. On the way to my Mom's house it was rainy with temps in the low 40s. I ended up with 28.3 MPG for the trip down, and was disappointed, but temperature effects mileage so I did not give up hope. The way home was sunny and about 55 degrees, and I made it home with 31 MPG. That's 2 MPG  better than I have seen before on this trip so I am on the right track.

With all the vents blocked (except the small strip in the leading edge of the bumper), the engine temps remain normal. The under-hood temp sensed by the Scanguage (intake air temp) does go over 100 degrees after driving for a while in stop and go traffic, and because of this I need to add an LED to my dash to show me when the electric fans are running, Also I will probably need to either add variable vents or remove the big lower grill block during the summer.

October 2013
I have just been driving the car and not modifying it except for the addition of some LED lights. The car is getting old and I removed rear mud flaps while fixing some rust. For the past several years the large lower front grill vent has been blocked, and the upper ones are open. This seems to work fine even on hot summer days. There is a big rust spot under one of the rear spoiler mounts, so that may go away soon. Gas mileage is about 30 MPG highway in the flatlands but it suffers in mountainous areas.
 

August 2015
Many newer cars and SUVs have tire fairing flaps in front of each tire. This seemed like it would be something easy to try on the now 17 year old Maxima. I noticed that the flaps on most care are actually mounted so they fair the tire and the suspension. About half the width of the flap covers the inside portion of the tire. I fabricated flaps that are 3" by 6"and made from 1/8" Lexan plastic that I had left over from another project. I installed them in front of each tire, in line with the leading edge of the wheel well..

In this picture you can see the Coroplast lower grill block that I added in 2009 and that the license plate was moved to just under the bumper. Its hard to see but you can also see the clear plastic wheel fairing tab.

Here's a better picture of one of the front wheel fairing flaps.
Here's one of the rear wheel fairing flaps. Also I added some plastic in front of the tab to help mount the tab and to close off an area under the car.

Yes, this car is getting pretty rusty.

I will be keeping an eye on the Scangauge during the next few highway trips and report the mileage back here later.

September 2015
I took the car on a fairly long trip and averaged about 29 MPG one direction but it was into a stiff wind. On the way back it averaged 31.5 MPG. It was into the wind again but a lower wind and it was at an angle

November 2015
After several more long trips I can see the car is now returning a consistent 31.5 MPG during mixed highway driving.

 

Vehicle Speed Modification MPG Change Temperature
1998 Nissan Maxima 65 MPH Partially blocked grill 29.0 - 80 degrees F
1998 Nissan Maxima 65 MPH Lower grill blocked, remove mudflaps, 4 x 4 ft square of belly pan. 31.0 +2 MPG 55 degrees F
1998 Nissan Maxima 65 MPH Add tire fairing flaps 31.5 +0.5 MPG 85 F, 33 F
1998 Nissan Maxima 65 MPH Full belly pan ??      
   

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