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Discussion Starter #1
Need some assistance. Just got back from a 1800 mile trip and only averaged around 14 +/- MPG on the highway. Saw up to 15.5 and as low as 13.5 MPG between fill ups. Just family of four and luggage, no trailer.

Same trip in the summer while pulling a motorcycle and enclosed trailer even got me between 10-12.

It is winter and I was doing 80-85 a lot of the way but still would've expected 16-17 MPG especially since we weren't hauling the trailer.

I used to get upwards of 20-21 MPG on long trips but since we pulled that trailer on a 2000 mile trip, mileage has seem to suffered a lot.

Am I off base or could something be wrong?
 

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I was doing 80-85

THATS WHY.
 

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80-85 isn't the lunatic fringe for expecting decent mileage. I managed nearly 20 on Christmas Eve at speeds of 70-75.

Is your truck stock? Heavy headwind? How many miles are on your truck? Check your tire pressures even if TPMS is not going off. You may have an old O2 sensor (or sensors) and their inaccuracy may be unnecessarily causing your ECU to dump more fuel into the cylinders.
 

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80 85 for sure. What highways were you on? What year is your truck. How much idling time do you do? All those factors have a lot to do about fuel mileage along with what has been mentioned.
 

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I'm wondering about this. 14+/- seems low if not towing. There aren't too many places that I drive that one can sustain 80-85 mph for more than 10 minutes without hitting traffic which will slow you down. It would be worse nearer to big cities. I haven't even tried such a thing since I was about 20 years old....a long time ago.

So I'm thinking of the old driving rule "no jack rabbit starts". If I were in any sort of traffic trying to maintain 80-85, it would require a heavy foot, some strategic braking, and a very keen awareness of the road during the holiday drive time. Add 1000 pounds or more of passengers, fuel, and luggage and winter blend gas, low tire air pressure due to cold weather. The perfect storm for bad fuel efficiency....conditions, weight, and speed. No way it is going to maintain those EPA ratings.

It would be interesting to let someone else drive the truck on a longish trip and go the speed limit (or less) and see what the fuel mileage is. I can easily beat 14 mpg in full city stop and go driving.

The only other factor that comes to mind is if the battery was changed and the computer has not been able to establish the necessary fuel trim data to maximize the gas mileage. Outside shot. It might be worth a quick trip to the dealer to have them plug up the diagnostic but they will want some money for that.
 

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I managed nearly 20 on Christmas Eve at speeds of 70-75.

You too are getting better than most RL MPG averages. Good deal.
 

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Hard to know for sure, but 14mpg for highway (non towing) driving seems improperly low, even if driving 85. Some more particulars about miles (on the truck) maintenance, tires, alignment etc might be helpful. Do you have a lift or oversize tires?
 

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Discussion Starter #9 (Edited)
It is a 2008 RT with around 58K miles. Had it since new. This past trip saw us driving from El Paso to San Antonio to Oklahoma and then back to EL Paso. Lots of open flat stretches of road with speed limits of 75 and 80. Which meant I was doing 80-85.

We moved from NC this past June and towed an enclosed trailer with a fully dressed touring bike and got 10-12 MPG. Just prior I swapped in a K & N air filter, and a new set of Kumho tires on the OEM wheels. They were a budget purchase and probably account for 1 or 2 MPG themselves. The truck is entirely stock with no mods.

No obvious indications that there is an alignment or tire defect; no pulling or excessive vibration in the steering.

Despite the wind, which there was plenty of, 13 MPG on the highway is alarming.

Thanks for the input. Keep it coming!
 

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do you remember the RPM's when you were doing 80?? At 70, my 2013 RTS does about 2000 rpms. If yours is a lot higher maybe overdrive is not working.

just curious, have do done a transmission fluid change ???
 

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Deduct 1-2 MPG for the non-OEM tires (not that we know them to give poor efficiency, just that we don't know them to be good, and they are a substantial change from previous known-good results).

Deduct 4 MPG for the speed differential from the sweet spot around 55 MPH (I went through some metric conversion and extrapolation from my own highway tests at various speeds for that guess).

Deduct 1-2 MPG for winter fuel.

Deduct 1-2 MPG for wind. We don't know what directions you were facing, but I'm guess that mentioning it means that there was more headwind than tailwind overall.

Deduct 1 MPG for a pre-2009 model year, if that's what you have.

Suddenly, driving under your current conditions and getting 14 MPG average doesn't seem so implausible.

My advice is to top up your tire pressure to 35-36, fill up with premium fuel (to offset winter fuel, ethanol, etc), and go for a long test on level ground on a non-windy day with low traffic. Don't pass. Drive no faster than 60-65 (55 is better). Disregard warm-up time (first 10 minutes or so). If you get 20+ MPG, your truck is fine except possibly for the tires. With OEM tires, I would expect 22+ under these conditions.

If you have a trip computer, reset it to zero after ten minutes of warm-up and drive for 30-50 miles with no speed change. Then turn around, get to highway speed and do it again for the return trip. Average the two readings to rule out wind or elevation effects. If you don't have a trip computer, you'll have to judge with a much longer travel period, which may involve more accelerations and warm-ups (which will decrease overall economy and accuracy of results).
 

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I seriously doubt the non-OEM tires are affecting mileage that much. This is pure speculation at this point, but I'm guessing the tires are OEM size AP51s which I have on my truck as well. I don't like them either, but their rolling resistance cannot be appreciably different from the stock tires. If anything I'd say they're less. Definitely not enough to justify a 10% - 20% difference in MPG. What were your tire pressures?

Winter fuel has less energy than summer, but only by 2% or less. Most people notice a drop in mileage during the winter as it can take longer to bring the truck up to operating temperature, and there is more fuel burned in this period. This is negligable if you only start the truck once or twice for an entire tank.

Having a head wind and a high average speed can definitely hinder your mileage. So could a fully loaded truck. Though the engine's primary job at speed is to overcome wind resistance, with four occupants and a full trunk (and bed?) you could be hauling around several hundred extra pounds.
 

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... but remember that if tires are larger diameter, you'll get under reported MPG (your actual mileage is better than reported), and you are going faster than speedo indicates. I didn't see an answer to tire size, so this may not be a factor.
 

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I drove to CT (and back) for the holidays from Charlotte this year. It's a little over 800 miles each way. My RL does relatively well on those kinds of trips. I got 20 mpg overall.
 

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Discussion Starter #16
Standard tire size for the RT - 245/65 R17. Kumho Venture APTs. Tire pressure on all four was set at 32 the morning of departure.

Not sure about the rolling resistance on them. Took a mile or two of MPG just based on reading the reviews prior to purchase.
 

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From all you have said, Speed, wind, winter. Remember you are trying to move a brick with an under powered V-6 engine with ethanol.
 

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It is a 2008 RT with around 58K miles. Had it since new. This past trip saw us driving from El Paso to San Antonio to Oklahoma and then back to EL Paso. Lots of open flat stretches of road with speed limits of 75 and 80. Which meant I was doing 80-85.

We moved from NC this past June and towed an enclosed trailer with a fully dressed touring bike and got 10-12 MPG. Just prior I swapped in a K & N air filter, and a new set of Kumho tires on the OEM wheels. They were a budget purchase and probably account for 1 or 2 MPG themselves. The truck is entirely stock with no mods.

No obvious indications that there is an alignment or tire defect; no pulling or excessive vibration in the steering.

Despite the wind, which there was plenty of, 13 MPG on the highway is alarming.

Thanks for the input. Keep it coming!
K & N air filter? Hmmmm Just the filter element or did you do the complete "Cold air Intake" Some people who put those on vehicle believe it will help the engine "breath" easier and makes it sound better. That usually equals foot further in the floor, thus lower fuel mileage.
 

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Discussion Starter #19
Just the filter. Considered doing the whole intake system but read elsewhere that the Ridgeline already has an optimal stock air intake system. Cost not worth the return I assume.
 

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Stock LTXs aren't that great on rolling resistance. Plenty of new tires out there (including the Mich LTX MS2s and the Lattitude Tours) with better performance in this category. I would highly doubt that there is anywhere remotely close to a 1-2mpg deduction due to the Kumhos.
 
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