: Gas miles -- Standard DeVille vs DTS



K0UZE
08-08-04, 10:05 AM
My wife and I rented a standard DeVille (2004) on a recent trip. We liked it well enough to buy an '02 DTS with about 15K and the 100K 6 year warranty. It was very easy to get about 25 mpg in the rental vehicle. I was a bit unhappy to find that the DTS does about 20 to 21 when driven similarly. Then I had the DTS in for some minor warranty work and the dealer gave me another standard '04 DeVille. Again, 25 mpg pretty standard. I mentioned the lower mileage to the dealer and they recommended a fuel injector cleaning. It made no appreciable difference. So what's the story? Do the '04 models get better mileage than the '02s...or does the standard DeVille do better than the DTS? And in either case, any theories on why? I love the DTS but I am not too happy about giving up 4 to 5 mpg. Any observations will be much appreciated. Thanks.

Ranger
08-08-04, 09:28 PM
What engine does the DTS have? If it has the 300 Hp then it will also have the higher final drive ratio and the milage you are getting is about right for that engine and final drive.

Ralph
08-08-04, 09:32 PM
Driving my Dad's 2003 DTS home (maiden voyage) it averaged 25-27 highway, about the average for my 1991 4.9 also.

K0UZE
08-09-04, 08:19 PM
It's the 300 hp version. Logically, one would expect a slight degradation in mileage with the more powerful motor, but that still doesn't square with Ralph's report of 25+ mpg on the road. Like I say, I get about 21 or so. Perhaps they fiddled with the engine management programming to get better mileage starting with the '03 models.

I have not been able to find the final drive ratio in the owner's manual, either.
Of course, lower gearing could also adversely affect mileage.

This is certainly a small gripe, because otherwise the car is really great.

Thanks for the feedback.

gserep1
08-09-04, 08:36 PM
Are you using the same type of gasoline? I understand that the newer versions of the Northstar use regular gasoline, while older engines use Premium. I have a 98 STS, and cannot use regular gasoline without sputtering and loss of power.
GSEREP1

Ralph
08-09-04, 09:50 PM
Could viscosity of oil be affecting the mileage? Tire pressure? It's my general understanding that thicker oil reduces mileage. Just a thought.

Ranger
08-10-04, 12:25 PM
Are you using the same type of gasoline? I understand that the newer versions of the Northstar use regular gasoline, while older engines use Premium. I have a 98 STS, and cannot use regular gasoline without sputtering and loss of power.
GSEREP1
You can use reugular. I use it in my '97 and don't even notice the difference. The knock sensors will retard the spark as required. If you are going to race it and want absolute best performance, that is another story but for general driving you should have no problem with regular.

gserep1
08-10-04, 06:05 PM
EVEN in a 98 STS? It would be nice if I could run regular gas. I am going to do a top end cleaning before I change the plugs and wires. Hopefully this will help decarbonize the heads and allow the use of regular gasoline. I'll give it a try, but if performance drops off significantly, or fuel mileage drops too far, I will switch back to 89 or Premium.
GSEREP1