Fuel Economy Tanked

[Jayhawkeye3]

Over the last two highway trips (60 miles round trip), I’ve noticed my fuel economy has tanked dramatically. It was around 26-28, but as you can see in the pictures, it’s dropped down to 19ish.

Any ideas what causes this? Maybe because it’s still new and burning in?

Yes I know my level and bigger tires impact on coming, but not this much. I’m actually getting BETTER economy in city driving 35-50mph speeds).

For this trip example, there was no wind, beautiful morning weather and fairly flat highway stretches.

I also did notice one evening my vehicle was dripping something that was falling onto a hot surface - hear the hiss in the third attachment. Edit I can’t get the video to upload, but every 30-45 seconds I would hear a drop then a hiss onto a hot surface.

 

[Fless]

TYF can't host videos, so use YouTube or another host and post the video link here.

 

[DuraYuk]

I wouldn't worry about it. You need to be looking at a bigger average spread like 450 miles. And compare 450 to 450.

Those short trips can be strange. Especially if it regens during the trip will kill short term milage but regains it thru the average.

The water is AC condensate. Normal

 

[2024 White Tahoe]

Over the last two highway trips (60 miles round trip), I’ve noticed my fuel economy has tanked dramatically. It was around 26-28, but as you can see in the pictures, it’s dropped down to 19ish.

Any ideas what causes this? Maybe because it’s still new and burning in?

Yes I know my level and bigger tires impact on coming, but not this much. I’m actually getting BETTER economy in city driving 35-50mph speeds).

For this trip example, there was no wind, beautiful morning weather and fairly flat highway stretches.

I also did notice one evening my vehicle was dripping something that was falling onto a hot surface - hear the hiss in the third attachment. Edit I can’t get the video to upload, but every 30-45 seconds I would hear a drop then a hiss onto a hot surface.
View attachment 468588View attachment 468589

Who took the first picture while driving 75 mph?

 

[Scarey]

I thought the babymax redlined at 5k not 6.

 

[Jayhawkeye3]

Who took the first picture while driving 75 mph?

lol. Wifey from passenger seat.

 

[swathdiver]

A heavy rainstorm and or a headwind can tank your instant economy.

I remember once driving along and watching the instant economy and we hit a torrential rainstorm and the truck lost 3 mpgs immediately.

Start a log recording your engine hours and odometer reading. Remember, distance and time equals speed. Once you know the average speed of a tank of fuel, you can get a correlation to the percentage of city and highway driving and more accurately, how many gallons an hour you are burning at a certain average speed.

 

[Stbentoak]

I wouldn't worry about it. My 2025 is all over the map. I'll go along for days, and it'll average 24 to 26 miles per gallon, and three days later we are under 20 for a day or so. How I judge it's doing is when I make a 150-mile trip to my daughters. At 75 miles an hour I'm still averaging 28 miles per gallon. That tells me that she's running pretty good. City driving is way too variable to have a lot of expectations.

 

[Jayhawkeye3]

Today’s drive:

Warmed her up for 15 minutes.

Super cruise at 78 for 25 miles.
46 degrees no wind hardly any traffic.

16 mpg

 

[DuraYuk]

Today’s drive:

Warmed her up for 15 minutes.

Super cruise at 78 for 25 miles.
46 degrees no wind hardly any traffic.

16 mpg

Dude 25 miles? Stop looking at short trips or you will go crazy. Look at your 450 average.

 

[JayceeP]

Unless your trip is hilly you shouldn’t be seeing anywhere near 16mpg over 25 miles of highway. Should be able to hit 20 minimum in good weather.

 

[972sparky]

The 15 minute warm ups sure won’t help fuel economy especially on short trips, will also cause sooner DPF regens that pull down the short term average as well due to the fuel injected into the exhaust system to help burn out the soot buildup. I get regens about every 250 to 300 miles on combined no towing driving.
I’ve watched mine go from 28+ down to 20 during regen but comes back up fairly quickly when it is done.

 

[Jayhawkeye3]

Dude 25 miles? Stop looking at short trips or you will go crazy. Look at your 450 average.

17.8 average 2k miles in.

 

[dkad260]

15 minute warm ups sure won’t help fuel economy especially on short trips

This.

OP....I'm not sure exactly how you are calculating your fuel economy, but you cannot factor in any warmup time. Get the vehicle ready to go, and reset at the start of the long road trip or when you fill the tank. Now that it's colder outside, any remote starts for extended periods will bury your AVG MPG.

Now you have big tires which likely have a higher rolling resistance, cold dense air is also harder to push through.

What about driving habits....any full-throttle launches? Only takes one or 2 to make a good dent in AVG MPG.

 

[Stbentoak]

This vehicle really doesn't need much warm up. It warms up faster than any vehicle I have ever had. My needle starts moving up within about a minute of driving down the road.

 

[dkad260]

This vehicle really doesn't need much warm up. It warms up faster than any vehicle I have ever had. My needle starts moving up within about a minute of driving down the road.

We also need to factor in the area where the OP lives/ conducting these MPG tests. If the ambient is much colder, short drives with cold fluids, cold dense air, possibly lower tire pressure if the OP hasn't compensated for the cold air, etc all play a factor. Also OE tires compared to larger tires with an aggressive tread and what also looks to be a slightly lifted vehicle.

What time frame and ambient air temps is the OP comparing these new MPG's to? If anyone has flown a plane, knows that 80-90 deg humid air is FAR different then 30-40 deg cold dry air...especially with a 152..lol.

Will it make this much difference in these findings......I don't know for sure. I'm just throwing out very likely variables.

 

[Jayhawkeye3]

Economy still leaves a lot to be desired at 3,500 miles.

Drove about 600 miles the past several days and haven’t gotten better than 17ish on the highway. Yikes.

Today for example:
- see picture, 100 miles at 70-80 mph
- rpms around 1400-1600
- cruise control on
- no wind, 55 degrees out
BELOW 17 MPG

I do have big 35” nitto grapplers, but no way those should reduce mileage by ~10.

Like I said, yikes.

 

[dkad260]

100 miles at 70-80 mph

Safe bet 70-80 is a huge factor. Did you also lift the body?

I do have big 35” nitto grapplers, but no way those should reduce mileage by ~10.

Which model Grapplers do you have? I assume new wheels also? If so what's the weight of the new wheel and tire compared to the old?

Cold dense air plays a factor.
Larger tires, especially if they have an aggressive tread plays a big part.

All combined it's very likely to hurt your MPG's.

Do you have the original tires and wheels? If so put them back on and do a hundred mile cruise at about 60 miles an hour and see what you get.

My MPGs at 60 MPH is much different than at 80 MPH with my 2012 6.2, 19-20 MPG compared to about 15-16 MPG.

 

[Jayhawkeye3]

Thanks! I think you nailed it.

The new grapplers. Terra I think?
Had it leveled too.

My mileage around the city suburb streets is like 20

 

[Yukonmax]

Economy still leaves a lot to be desired at 3,500 miles.

Drove about 600 miles the past several days and haven’t gotten better than 17ish on the highway. Yikes.

Today for example:
- see picture, 100 miles at 70-80 mph
- rpms around 1400-1600
- cruise control on
- no wind, 55 degrees out
BELOW 17 MPG

I do have big 35” nitto grapplers, but no way those should reduce mileage by ~10.

Like I said, yikes.

Sounds about right my Yukon took a 10 mpg hit with mickey thompson 35s