robarsan

Since having a B12 service done on the RL last week I have noticed about a 2 mile-per-gallon increase. I would expect a small change for the better with a new air filter but this seems a bit extreme.

I take the same route to work every day which is about 70% secondary roads and 30% highway. For the past year I have hovered around 22mpg. Since the service, it has consistantly been above 24mpg.

Not complaining of course, just curious if this is normal.

kirbyflorida

You may have had a really dirty air filter, in which cases, change it more often.
Warmer weather will also help.

TampaRLX-SH

Although it does vary by region, perhaps in addition to the air filter the summer grade fuel is now in your area? I notice an increase in fuel efficiency in the summer (even with A/C on).

Perhaps also, your tire pressure was increased in the Service Call? An increase of as little as 1 PSI can improve your mileage. Could be all of the above but at least it improved!

foam4me

2006 25k

Just bought the car and no service done yet so these stats are a baseline.

1st tank, mostly interstate 26 mpg
2nd tank, daily commute on local Boston streets 22 mpg. I was pleasantly surprised about the local mileage but think that the driving style was especially conservative as I knew the mileage would be less than the 03 TL I traded.

robarsan

You make some valid points. I didn't even consider the possibility of the change to summer grade fuel.

It was up in the 70's and low 80's all this week and the AC has been on; I don't know if that would negate any fuel change benefits.

I still have the "nitrogen filled" snow tires on, so I didn't have them rotate the tires, but they could have topped them off if they were low. Anyway, I'll be putting on the summer tires this weekend, and will just appreciate the additional fuel mileage while it lasts

VOdoc

Check your average speed on the MID. Recently with the gas price increases, there seems FINALLY to be a slight reduction in traffic volume. That has translated into a 3 mph higher average speed on my commute (from 33 to 36 mph) and a 1.5 mpg improvement in gas mileage (from 20 to 21.5 mpg). Once it hits $5 a gallon I am hoping for full speed and 25+ mpg!!

robarsan

That's another good point, but that wouldn't apply to my situation. I opted for a very early flex schedule at work so I get in early and out early. The traffic is not an issue....yet. I live about 5 miles from the ocean so there will be the perenial gridlock from about mid May to September.

Chas2

If anything, your nitrogen filled snow tires have a higher pressure than required, with increased temperatures, so that may be another reason for better mileage, decreased rolling resistance. Very little, but maybe all these very littles, add up--tire pressure, clean breathing, summer fuel, etc.

foam4me

Unless the tire pressure was exceptionally low it seems unlikely that "topping off" would make a dramatic difference and snow tires have notoriously high rolling resistance because of the sticky treadface rubber compounds.
More likely the originally suggested new air filter and we had some warm weather during that week which would have reduced "choke" (rich mixture) time during warm up.
With gas prices these days any mileage increase is welcome, whatever the source!

On that note has anyone tried lower octane fuels? The Owners Manual advises against it but with modern knock sensors and the willingness to accept a little loss in performance I wonder how much, if any, damage is done.

robarsan

Thanks for all the replies.

Just switched over to the summer tires this morning. This will be a good opportunity to pay closer attention to my driving habits and the causal factors mentioned in this thread that can influence the fuel mileage.

cai06

You can use lower octane fuels without damaging the car, however your efficiency will decrease with no real life advantage. This is a high compression engine so it gets its best MPG with high octane fuel.

Chas2

That is what I understand. Your mpg actually goes down using lower octane fuel, so your savings can be eaten away by the inefficient use of the engine.

4bearhug

I actually tried this in my 04 TL just to see how much of a difference in MPG I got on lower octane fuel. I tried it over several months so to get an accurate reading. The worst difference I ever got was .5 MPG and most of the time the difference was zero. It seemed to be such a small difference to be insignificant. YMMV

nralpmet

Curious. Also just had the B12 (43k km on an '05) and have noticed better mileage (kiloage?). Thought my driving had improved 8-)

Chas2

Maybe that air filter change is really important. After all the pollen is over, I think I will change mine. My NBP looks like a Black Forest Green with all the pollen on it.

foam4me

Hmmm.
0.5 mpg/23 mpg (avg)=- 2.2% loss in mpg
$0.10 gal savings/ $3.50 gal cost= 2.9%

You're right, hardly worth the effort.