Lack of power and high fuel usage while towing

[TeCKis300]

As these engines have sophisticated engine controls and diagnostics, I doubt the problem lies within the fueling and closed loop functions of the engine. Short and Long term fuel trims that would cause such bad gas mileage would have tripped a CEL.

It still sounds to me like a plugged cat, plugged intake, super bad aero, dragging brakes (though I agree with Dan that you would have smelled something, hundreds of miles back). It's also possible with your 34's, that you're in the really high load portions of the fueling maps such that the motor runs super rich and your torque converter never locks up. Which is why I mentioned I tow with 33s and I haven't really noticed that, even when running in S5. If you're running in S4, surely the motor is in it's good powerband.

 

[Chocolate]

Toyota/Lexus states 2015 LX570 curb weight 6000 lbs

Toyota puts that same number out there for all models of the 200 LX, but Motor Trend weighed a 2015 LX and got 6,109 pounds. The 2016 LX which is 2.4" inches longer (199.4" vs 197") weighed in at 6,230 pounds.

 

[JBHorne]

Heading back. On phone so I'll make this quick, but lota of good info above. I was being generous with the weight loaded - I'm probably significantly less. Trailer brakes aren't dragging. No smell or heat.

So on level ground I was just doing 55 in 3rd gear at 3500 RPMs. Note my speedo is off by about 5mph. Speed confirmed by GPS.

I took a photo but can't post it now. AIT was at 149*F and it was 79*F outside. No idea how there is a 60* intake temp difference. Is that normal?

Going to the dealership this week.

 

[Dan Higgins]

Good luck! My setup is so different its probably not good to compare. But needing to turn 3500 RPM to maintain 55 on level ground (unless you have huge headwinds) seems off to me.

 

[Dan Higgins]

Just a data point. I had to check out my hitch receiver height after the modest lift I did last week so I took the trailer for a short pull. Here are the numbers:

• LC weight ~6500-6800
• Trailer weight ~5500
• Trailer height ~10'
• 5 minutes at 55MPH on "flat" highway
• Tranny set to S6 (8-speed)
• RPM ~2000
• Avg MPG during that 5 minutes per Info display ~11
• LC is a 2016

 

[InkMing]

Just throwing some of my data in there.
2014 LC, fully loaded with family and gear, rock rails.
Running BFG All Terrains.
Pulling a Coleman Evo3 fully loaded with water and supplies.
2 hour drive to where we camp, about 110 miles. With the inclines and one steep grade that we ascend, I get about 9-10 MPG on those tanks.
Figure the popup is weighing in around 5,000 lbs.
I average about 13.59 MPG when not pulling the trailer. Now on the last couple tanks when the family and I were taking a trip of mainly highway miles and using the cruise control, was getting around 15-16 MPG per tank.
One thing that I have found that works well is using the cruise control. It really bumps up the MPG more than me trying to maintain a steady 60 MPH or 65 MPH.

 

[linuxgod]

Another data point for you. I have a 2013 LC. I have 34s. I haven't weighed it, but with my mods I expect it's about 6500#. My trailer is 5000# when loaded (tongue weight ~600#). I tow in 4th gear and at 65mph it hums along at about 3000 RPMs. In the flat midwest I get about 15MPG on the highway without the trailer, and about 10MPG with it. (That's per the MID on the dash, which reads low due to tire size - my actual mileage is about 5% higher).

When I pulled my trailer through Colorado this summer I averaged about 7.5MPG. There was a sub-6MPG low point when I filled up in Denver and then went up through the mountains heading to Breckenridge, but it averaged out over the tank. I definitely found myself in 3rd or 2nd when climbing some of the steep grades out west. So 6MPG on a 3000# trailer on flat land, regardless of the altitude, seems very low, even if your LC is 8000# with armor.

Side note: the LC manual says to tow in 5th. I have an OBD2 reader and I find if I tow in 4th my transmission temp stays under 200F when in the midwest (300' above sea level). If I tow in 5th it runs hotter. Even in 4th when I was out west at 8000-9000' altitude the thinner air added 10F+. The hottest I've seen is 240F coming off the torque converter and about 220-225F in the pan, but that was running in 2nd gear up the mountains in Colorado.

Questions for you:

• What octane fuel do you run? When I filled up with fuel around Bryce Canyon (at 8000') I bought 85 octane. On the way back we went through Grand Staircase. There was one point later where we were at about 9000' traveling downhill at ~45mph but I found I had to keep it in 3rd to keep my speed up. Even though I was going downhill. I promptly topped my tank with 91 octane (about half a tank) and didn't experience that again
• Does the vehicle pull to either side when not towing? This would happen if the brakes were dragging on the truck
• Are you sure the brakes aren't dragging on the trailer?
• When was the last time you had the wheel bearings on the trailer repacked?

 

[linuxgod]

One thing that I have found that works well is using the cruise control. It really bumps up the MPG more than me trying to maintain a steady 60 MPH or 65 MPH.

Depends on the speed you have it set at. At 60, definitely. At 70, not so much.

The OP said he was doing 60-65, so I didn't mention it, but I have found that when towing for every 5 mph I speed up I lose about 1 MPG. i.e. I get 6MPG when towing 75, 7MPG when doing 70, 8MPG at 65, etc.

 

[TonyP]

Also, the mpg gauge isn't exactly spot on accurate.

 

[Tremek]

Last year when my '13 LC was stock I towed a ~2000lb car trailer and my ~4500lb Cadillac on it out to Reno and back to Denver. I towed in 4th, more or less averaged 10mpg the entire way there and back (taking 80 - less mountainous terrain than 70.) With the armor and BFGs and higher ride height etc on it now I wouldn't be surprised to see that dip to something like 8-9mpg average while doing something similar...

They're thirsty trucks, especially when we bolt all this extra stuff to them! While we're airing grievances, the gas tank is too damn small too. I picked up a 2500 Suburban last month for towing and running around the kids, and its 38 gallon tank is spoiling me.

 

[Sandroad]

Wind resistance is a real killer of gas mileage when towing. Weight is the big factor when pulling relatively slowly up the mountains, but on the level, wind pushing against the trailer is what empties the tank fast, whether the wind is created by forward motion or by actual wind blowing you back. Wind force is not linear; it varies with the square of the speed. Doubling the speed means 4 times the force. Of course, it's more complicated to calculate what happens when towing, because wind drag (friction) figures in based on the shape the trailer, etc. But, mpg goes down fast as speed increases when towing. When deciding what's "normal" for your rig, factor that in.

 

[TeCKis300]

^Right. I find it more relaxing to drive with a trailer in tow, since I'm generally with the flow of semi trucks and not trying to get ahead. In CA, with the 55mph speed limit when towing, that mean 55 - <65mph.

 

[Cruisin911]

34" tires + 3.91 gears + trailer + add on weight = dismal power when towing. My tundra had the 5.7 and 4.30s and towed WAY better than my LC (same trailer, same wheels, same tires)

 

[TeCKis300]

^That's where the new 8-speed trannies really start to shine. Lower ratios in the first couple gears, and more ratios to choose from.

Fully loaded and packied for a 10 day trip. 420 mile tow up CA today towing at ~60-63mpg. Avg 9.5 mpg per the display. Compensating for the 33.2" tires, that edges me right over 10mpg. Thirsty, but not bad considering. And I have a 3.5 gallon tote for my generator as backup, so I'm not afraid to run the range gauge near or past 0. Helps a bit, but it's still a small tank.