For all of you out there that have an STS4 with the 5 speed auto and V8 (05 and 06 models?), what kind of highway mileage are you getting with your cars?

We just purchased an 06 model STS4 fully loaded with the Northstar. We love the car, but I have noticed that the highway mileage isn't what I would expect.

We took a roughly 180 mile highway trip on a flat open interstate (I 40 from Raleigh to Wilmington NC) and went mostly between 80 and 85 MPH the whole way. According to the onboard computer, we averaged right at 20 MPG. The same trip, same driver (me), and at the same speed in my STS-V gets around 23. Our old FWD 99 STS would get around 28 on this same trip.

Is this normal mileage from this setup?

That is about the best you can expect. In fact, it is better than I would expect at that speed.

Thanks, Eric. I just wanted to make sure that this was normal. We're slowly weaning ourselves off of the FWD architecture and it's fantastic mileage figures.

I much prefer the way these RWD/AWD cars handle over the FWD previous generation STS and Eldorado that we used to have, but those cars really did get great mileage for how powerful they were.

For all of you out there that have an STS4 with the 5 speed auto and V8 (05 and 06 models?), what kind of highway mileage are you getting with your cars?

We just purchased an 06 model STS4 fully loaded with the Northstar. We love the car, but I have noticed that the highway mileage isn't what I would expect.

We took a roughly 180 mile highway trip on a flat open interstate (I 40 from Raleigh to Wilmington NC) and went mostly between 80 and 85 MPH the whole way. According to the onboard computer, we averaged right at 20 MPG. The same trip, same driver (me), and at the same speed in my STS-V gets around 23. Our old FWD 99 STS would get around 28 on this same trip.

Is this normal mileage from this setup?
Hi dhemrick,
that`s the price for AWD, but 20 mpg (about 11 liter/100 km) isn`t bad by doing around 85 mph.
One interesting thing for me, your STS V gets at the same speed about 23 mpg and I might trade my STS V8 export model for a V, since they now available here in Germany.
The avg mpg on my STS here in Germany is around 17 mpg but I drive speeds up to 165 mph.

Harry

I get 22MPG over a long trip averaging 65-70MPH

STS4 20 miles per gallon on Highway

One reason is the '05 (and, I think, the '06) STS4 came with a 3.42 gear and a Gas Guzzler Tax. The other N*s got a 3.23 gear and the V6s got about a 2.91 gear (I think). My '08 1SG has a 3.23. Either way, if there is a hole in the trraffic, you OWN it. As they say, It will pass anything but a gas station.

My V6 STS AWD gets 23-24 on the road, but I seldom go over 75.

Hi dhemrick,
that`s the price for AWD, but 20 mpg (about 11 liter/100 km) isn`t bad by doing around 85 mph.
One interesting thing for me, your STS V gets at the same speed about 23 mpg and I might trade my STS V8 export model for a V, since they now available here in Germany.
The avg mpg on my STS here in Germany is around 17 mpg but I drive speeds up to 165 mph.

Harry

Oh.... if ONLY we could regularly go that fast on our highways here. Unfortunately, speeding tickets are a huge moneymaker for local municipalities so we have to really watch our speed or pay the price. 80-85 MPH is about all I dare normally which really sucks when you know your car will do much more... especially the V. I've had it up to 100 a few times but not for long stretches. I miss the few drives I've taken on the autobahn. :crybaby:

19 to 21mpg is what I typically get in my '05 STS4 V8. I usually run between 80 and 90mph. Any faster and you stand out too much.

I have a 06 STS4 V8 and I get around 20 - 20.4mpg (75% hwy 25% city)

My V6 STS AWD gets 23-24 on the road, but I seldom go over 75. My V6 STS RWD gets 23-24 on the highway at speeds between 65-75. I don't understand why it's so low because my previous car was a CTS with the same engine, drivetrain and gearing and only about 250 pounds lighter and it got 27 mpg on the highway. I brought it back to the dealership after I got it last year but they couldn't explain the difference.

My V6 STS RWD gets 23-24 on the highway at speeds between 65-75. I don't understand why it's so low because my previous car was a CTS with the same engine, drivetrain and gearing and only about 250 pounds lighter and it got 27 mpg on the highway. I brought it back to the dealership after I got it last year but they couldn't explain the difference.
It's heavier, more moving parts, more friction, and higher rolling resistance.

My RWD V8 doesn't get much better...that "gas guzzler" tax that the STS4's had in 2005 still doesn't make any sense to me.

I paid gas guzzler tax on my '06 as well. The reason they charge gas guzzler tax is because it's a gas guzzler.

The RWD is not much better in the real world. One of the reasons I didn't get the AWD was beacuse of the tax. Not the up front cost on the sticker, but more because I thought it must get really bad mileage to justify such a penality. Even though the mileage estimates on the stickers between the two were not that different.

Now after having my RWD V8 for a couple years and with the mileage it is getting, and performance in the rain and snow...really wish I had purchased the AWD. Snow tires and weight in the trunk does help, but I'm sure it can't compensate for the AWD advantage in snow. Just too bad Cadillac couldn't have done something (gearing) to avoid the guzzler tax on the AWD. It just looks bad on the window sticker. And there are other cars in this class that do avoid the guzzler tax between their RWD and AWD versions.

I don't know...maybe it's that 200 pounds of sand in my trunk that's making the STS get such poor mileage. :)

Running the tire pressures up a couple of pounds all the way around helps some.