Fuel Economy?

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Mar 7, 2012
Eugene, OR
So I've been running 92 premium in my 99LC and with a mix of city/highway/forest roads. Got around 11 mpg this last tank. A couple of questions.

I recently switched to 285/75/r16 BFG AT KO2 tires. Will this larger tire size impact my Odometer enough to show a lower mileage (like it does with the speedo?)

Also, having recently added a 50" light bar above my ARB bull bar, I know I'm pushing more air, is that contributing some/most?

And I also added the ARB/outback drawer system. Love it, but not sure how much more weight I'm running with.

I keep my foot VERY light on the rig and don't speed. I run the tires a little high on PSI for less resistance, anything else I can do to improve on the slipping MPG?

Thanks, Spank
Your tire size does slow down the odometer and also makes your speed register ~5mph lower than your actual. To make sure you are getting the proper MPG readings, you will need to do some GPS tests. The good news is you are probably getting better MPG than you think, but not much.

Drop the Premium gas, its just a waste of money IMHO.

I have 285/70/r18s, front runner rack w/ light bar up top and my odometer/tank fill based MPG calc is ~11MPG on regular 87.

Not much else you can do.
Drop the Premium gas, its just a waste of money IMHO.

Ditto. There is less energy in premium fuel vs regular

I haven't checked since I upgraded tires but I used to get 16+ MPG. My LC is pretty much stock other than tires and running board removal
Did it get noticeably colder when the mileage dropped? That always drops my mileage by 2-3 mpg. Goes back up when the weather warms up.

Dump the premium gas. Not worth the cost given no benefit.
Ditto on the premium fuel. It's higher octane which means it burns slower. I've been using mid grade and regular in my 100 for years with no pinging or any other issues. But.....I live in flaaat Florida. If you get any pinging on the hills go back up a grade.
No difference in fuel mileage between premium and regular but it's a hell of a lot cheaper on a fill up.
May be due to the winter fuel blend. What kind of fuel economy did you get before the light bar and BFG's?

I too only run reg 87. I've dropped about 10% in fuel econ with the winter blend (more butane). Still seem to get about sticker 13 city / 16 hwy and do a bit better on Summer fuel. Stock '03 LC with Michelin LTX MS/2's at 32 psi.

If you're bored at work:
Great points and info guys (except for getting out and pushing!:moon:) I'll drop the premo and go back to regular. I always thought I got slightly lower mpg with premium, but believed I was miscalculating. hadn't remembered the switch to winter-blend. That could be part of it. Additionally, the forest roads were a trip into the cascades and temps did drop some along with 3000+ vertical climb. Sounds like a mix of factors.

Thanks again for the help!:cheers:
I use 87 in '98 LX and get anywhere between 12-14 with mixed driving. I did several tanks of 93 (consecutive), the extra cost isn't reflected in MPG increase. Light bar prob not huge factor if below roofline.

Clean your MAF, throttle body, reset by disconnecting battery, run a couple tanks of BG 44, and fill up at the same place, in the same manner to get a true reflection of MPG. There are calculators online to help with tire conversion.
Drop the Premium gas, its just a waste of money IMHO.
We have two (2) 1998 LC's. My wife has 265k, mine has 215k. We generally never run premium fuel, just the cheapest stuff we can fine.
On rare occasion, I'll put premium in if I'll be driving at altitude or doing a lot of grades, but that's about once a year.

Thanks. I run Costco as well. Good to know I'm not "out of line" with mpg.
I agree. driving slower and enjoying the ride makes for much better MPG.
Running 33's I've been getting about 11mpg too. Probably 80% surface streets though. Get about 13.5 mpg all freeway :(
I just put 14 gallons of regular in and covered 217 miles = 15.5 mpg. That's about right with 60/40 Hwy/City mix of driving. Gas was $2.47 a gallon today so had to fill up even though I only needed 14 gallons lol!
with the combo of weight, winter blend, extra drag from light bar, and 285s or 33s, sounds like I just need to get comfy with 11ish.
I have a Yellabox but haven't installed it yet, so I've been keeping an eye on it via GPS vs speedometer. The 275/70-18s make my speedo run almost exactly 5 mph slower at 75 (registers at 70 mph on the speedo). Simple math (75/70) yields a difference of ~7%, meaning I'm getting about 1 mpg more than the numbers would indicate.
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I never saw over 10MPG average. I was on 35's with ARB and full rack. I could see 15MPG driving at 65MPH on a flat highway with light throttle adjustments. Gas mileage was never a thought when designing the LC. Hence the 25.5 gallon fuel tank.
Keep the RPM's below ~2100-ish when pushing on the skinny pedal, either accelerating or maintaining freeway-type speeds, and you'll see improvements. Easier to verify in an '03+ with onboard trip computer. Your wallet will thank you, but the people behind you will be pissed.

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