EdOz

I've owned my SL since December and have filled it with both 87 & 93. As posted in a previous thread, using one octane over the other will not result in a mpg change.

With that in mind...I just took - except for a few miles - an all highway trip. Mostly flat terrain, moderate temperatures (NJ, DE, MD), dry road conditions, used cruise control for almost all of 400+ miles. Tires perfectly inflated. SL has 11,500 miles on it.

The actual mpg was 28.4 (Maxima calculation was higher (as always) at 30.5).

The 28.4mpg, to me, seems likely to be the highest I can expect given the virtually ideal driving conditions.

Do you have another experience?

robtroxel

I think there is 4 to 5 more mpg to be had at highway cruising. Lots depends on the speed, wind direction and road surface. It you can tolerate the ride, boost the tires up to 37 pounds.
Mine gets 32/33 mpg on 87 octane at 67 / 70 mph on flat land Illinois roads with 18000 miles on the clock.

lightonthehill

Also keep in mind that cruise control does not necessarily give the best MPG. In fact, if the road is not completely and entirely flat, it is very easy to get a higher MPG without cruise control. This is for several reasons. One is that a human can see a rise in the road ahead and gently pick up speed to better handle the hill. A better illustration is that cruise control can actually hold back the speed on a gentle downhill slope in order to maintain the set speed, but without cruise control, the driver can let the car gather speed downhill in order to have momentum to carry the car further up the next slope before the car needs to increase RPMs to complete the climb.

There are other situations where this is true. I know that I get slightly better MPG in fairly flat country without cruise control, and significant higher MPG in hilly country without cruise control. The fact humans can see the terrain ahead, will not retard the car on downhill slopes in order to maintain a strict speed, and will not increase the rpms as we near the top of a steep climb just to maintain a strict speed gives a careful driver the advantage over cruise control.

Mason Hatcher

I travel from the Dallas/Ft Worth area to Corpus Christi a couple of times a year. About 450 miles one way. I can easily average 34 MPG when I keep the speed at or below 70. At 75 I drop off to 31-32.

We have two roads where the Speed Limit is 80 and then 85. At 80 I drop off to 30ish-29. At 85 MPH I cannot do better than 28.

That said, I average throughout the entire trip, by the computer and my calculations, about 30-31 for the entire trip.

gizzsdad

Copy and paste of my post from 8/16. This trip was fully loaded and with A/C on most of the time.

"I recently had a 1,500+ mile trip with my '16 Max. So we had a full complement of luggage and gifts.

I set the cruise at 72-73, which we maintained except for getting off the Interstate to get lunch (had to wait through two stoplights to get back on), and one section of about 15-20 miles of 60-65 around the Indianapolis beltway, and one section of 8-10 miles at 20-45 because of construction. Most of the time was with A/C on.

My average for the trip was slightly over 36 mpg going out, and slightly under 36 coming home - according to the on-board monitor. I did hand calculate one tank (308 miles on 8.151 gallons) that came out to 37.8 mpg. I may not have gotten that tank completely full, as I might have squeezed another 0.2 to 0.3 gallons in. If I use 8.4 gallons, that comes out to 36.6 mpg."

compyelc4

Took my '17 SL on a 120 mile round trip today. My wife and me. 80 degrees F and dry. About 80% interstate and 20% rural and city. Got a new best of 37.3 mpg. I am not fibbing! Actually 37.3 out (with AC not on) and 33.2 back home. Back home was using AC and a terrific head wind the whole way. Cruise speed on interstate was under 75 mph (using cruise control). I have 3200 miles on her as of today. I'm averaging 28.6 mpg since I bought her last December. It may have helped that I noticed 38 lbs of tire pressure all-around once the tires got hot today.

realmac

I hit a new best at 33.3MPG today. New engine air filter, Shell V-Power Nitro, mostly highway, light on the gas and not a ton of traffic.



realmac maxima 33.3MPG

lightonthehill

38 psi is normal when the tires are hot. When you re-check the readings before driving in the morning, the psi will be back down nearer 33 psi.

This psi thing goes even further than tires getting hot from driving. I keep the psi displayed most of the time on my Maxima, and even after leaving the car sitting an hour or so with the tires on one side in full sun and the tires on the other side shaded by the car. the psi of the tires on the sunny side will be slightly (usually one or two pounds) higher than the psi of the tires on the shady side.

We always need to be aware that tires that read 33 psi while sitting in the garage in summer will probably read below 30 PSI when sitting in that same garage in winter. Cold weather lowers the psi reading, although the same amount of air is in the tire as in summer.

The TPMS system will not indicate that a tire is low until the psi drops to around or below 28, but in early winter, we could be driving around with tires that are several pounds underinflated (such as 29 psi) and not know it. But if we check our TPMS display fairly frequently, we will see this happening, and raise the psi.

The TPMS system also allows us to catch a slow leak that may not drop low enough to trigger the 'tire psi low' alert for weeks, but in the meantime, we may have driven thousands of miles on an underinflated tire, resulting in more wear on the shoulder edges than in the middle of the tread.

Tires are vastly superior today than in the 1950s, when they required inner tubes, did not have belts, and seldom lasted 20K miles.

compyelc4

light-

Thanks for your quick and thoughtful comments. You are an asset to this site.

lightonthehill

compyelc4 - Thanks for the compliment. All I try to do is tell about the things that I have learned the hard way in driving since the 1940s. I have sort of 'evolved' over the ages with tires, and understand them. But when it comes to things such as modern automotive electronics, I am a total blank.

mrgooch

Yesterday I did 33.3 for an 1 hr 20 min. at highway speed 73 + miles MPH.

Sbradle4

The best mpg I've gotten so far is 31.9 mpg