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58K views 159 replies 90 participants last post by  the cadillac man 
#1 ·
CTS gas milage

Hello, i've got a 2003 CTS, and lately it's been getting horrible gas MPG, basically 18-20ish. I've just got the oil changed AND replaced the gas filter again, and still no change... I've alway put premium gas, as required, and still nothing better. It used to get at least 25 MPG. Any ideas??
 
#6 ·
Re: CTS gas milage

You may want to look at your driving habits. I've heard the ECU on our cars take about 100 miles to adjust to your particular style so, if you have been driving like a bat out of hell...you will probably get lower MPG for a while. My 03 owner's manual recommend's premium fuel. It says you can try the lower grade fuel but, if you get a knocking sound to go back to premium. I didn't believe there was actually a difference in the fuel but, sure enough I got a knocking sound. I think the newer CTS's recommend lower grade fuel.
 
#7 ·
Re: CTS gas milage

Thanks for the info... And I don't drive like a bat outta hell thanks, lol. And yes, the 03 was the first year, and it does require premium fuel, I got the knocking too, and returned to premium, quite some time ago. That's why I don't understand why all of the sudden the mileage, is so bad. But thanks for the info, and I guess it's just gonna be that way...
 
#8 ·
Re: CTS gas milage

Thanks for the info... And I don't drive like a bat outta hell thanks, lol. And yes, the 03 was the first year, and it does require premium fuel, I got the knocking too, and returned to premium, quite some time ago. That's why I don't understand why all of the sudden the mileage, is so bad. But thanks for the info, and I guess it's just gonna be that way...
If you've not changed the way you drive, one would think that there should be a reason for a fairly significant change in mileage.

Might be worth springing for a new air filter if you've not replaced it recently. Also check to ensure that your tire pressure hasn't dropped to the point where it may be a factor.

Of course, mileage will usually suffer a bit during winter months if you live in a wintery climate.

Are you throwing any codes that could indicate a leaking injector, whatever? http://www.cadillacforums.com/forums/cadillac-forum/t-46420.html

Good luck...
 
#10 ·
Re: CTS gas mileage

My brother has one of those machines to hook up to, to see if it's throwing any codes, that will be done this week... I did change the air filter as well a few weeks ago, that was my first thought... I think i have some fuel injector cleaner bottles in my garage, i think i'll throw them in the gas tank as well, i suppose that can't hurt anyway. Thanks!!!
 
#17 ·
Re: CTS gas mileage

Yeah, high grade is recommended for the 2003, but isn't required... Here's a cut-n-paste from page 6-3 of the 2003 CTS owner's manual pdf on mygmlink.com...

"Use premium unleaded gasoline with a posted octane of
91 or higher for best performance. You may also use
middle grade or regular unleaded gasoline rated at 87
octane or higher, but your vehicle’s acceleration may be
slightly reduced. If the octane is less than 87, you may
get a heavy knocking noise when you drive. If it is bad
enough, it can damage your engine."


Also, the 2003 without Nav is one of the easiest to read codes-on if you want to try http://cadillacfaq.com/faq/answers/codes.html - The page includes the link for deciphering the codes....

My brother has one of those machines to hook up to, to see if it's throwing any codes, that will be done this week... I did change the air filter as well a few weeks ago, that was my first thought... I think i have some fuel injector cleaner bottles in my garage, i think i'll throw them in the gas tank as well, i suppose that can't hurt anyway. Thanks!!!
 
#11 ·
Re: CTS gas milage

my 06 cts requires the lowest grade gas, the dealer made a point to me when i was purchasing my baby, that you should only put the lowest graded fuel, i was very suprised because going from a 93 honda accord to an 06 caddy, i thought i would definetly be a premium guy, to my suprise (and happiness) i dont have to.... THANKS GM!
 
#12 ·
Re: CTS gas milage

Its not your driving habits, the CTS gets really crappy mileage, but at least it runs on regular. I get about 10-12 in the city and 20-22 on regular 20-30 minute trips on the highway. Hopefully this SEVERE problem will be addressed in the next generation model coming out next year.
 
#19 ·
Re: CTS gas milage

Its not your driving habits, the CTS gets really crappy mileage, but at least it runs on regular. I get about 10-12 in the city and 20-22 on regular 20-30 minute trips on the highway. Hopefully this SEVERE problem will be addressed in the next generation model coming out next year.
ILLMATIC - I think you need to get your car in for service because I've never heard of anyone getting 10-12 MPG in their CTS.

Driving habits and "sport mode" definately play a role in your gas mileage. I used to keep my car in "sport mode" all the time and would average around 18-19mpg in the city. Recently I turned sport mode off and slowed down my driving a little bit and now I'm getting 20-21mpg in the city. On the highway cruising at 75-80 I average around 25mpg. I've seen as high as 30mpg average on a trip to West Virginia with an average speed of 60-65mph (county roads).

I always run premium gas and use Mobil1 oil (changed every 5000 miles). I've tried regular gas and though I didnt hear any knocking I could definately feel a difference in throttle response and accelleration.
 
#16 ·
Re: CTS gas milage

What do you mean by a knocking noise? I have something similar in mine but it almost sounds like a lifter noise. Could this be the same thing? Oh, I've always used regular (cheap stuff) in mine. My other car is a supercharged Z24 Cavalier. So premium in one car is enough for me! :)
 
#20 ·
Re: CTS gas milage

I took it to the dealer. Nothing's wrong with the car. The 10-12 mpg i get is in the city. I live in NYC and theirs a traffik light every couple of blocks. On the highway i get anywhere between 18-22 but to in all fairness my highway trips are very short 20-30 minutes tops. I've only been on the road longer than an hour on two or three occassions.
 
#21 ·
Re: CTS gas milage

I took it to the dealer. Nothing's wrong with the car. The 10-12 mpg i get is in the city. I live in NYC and theirs a traffik light every couple of blocks. On the highway i get anywhere between 18-22 but to in all fairness my highway trips are very short 20-30 minutes tops. I've only been on the road longer than an hour on two or three occassions.
Man youre missing out on one of the best features of the CTS, long haul road-trip comfort.
 
#22 ·
Re: CTS gas milage

I don't know my ride over the last 5k miles averages 18.2 mpg. I drive about 100 miles a day and 70 of those are on the highway. I usually drive between 75 and 85 on the highway. The CTS isn't great on mileage, but considering my driving habits it isn't that bad.
 
#23 ·
Re: CTS gas milage

I tell ya the gas mileage in the CTS is a whole lot better than what I got with the Ford Exploder that I used to drive. When I first got it as a hand-me-down from my dad it had about 40,000 miles on it and averaged about 14mpg in the city and 17mpg on the highway. By the time I got rid of it at 120,000 miles something must have been seriously wrong because the gas mileage had dropped to 8 or maybe 10mpg in the city and 11-12 on the highway.
 
#24 ·
Gas Mileage Low??

Whats up everyone. I have a 2007 CTS with the 3.6l engine and automatic trans. I have had it since new for about 7 months with 4700 miles. Recently I have been noticing with the past 4-5 tanks of gas that according to the trip odometer my gas mileage is under 200 miles to each tank. When I filled up today it even said I only had 190 miles until empty right after I filled up. I drive 5 miles round trip to work and have a remote start so I let the car warm up for 10 minutes prior to driving. I drive the car as normal as anyone else getting on the gas occasionally. My question is, is the trip odomoter and remaining miles gauge accurate? My previous car was a 2001 Trans am with a 5.7L engine getting 20 mpg so this doesnt seem right to me. This tank of gas I am going to check by the actual odometer. I am also wondering if not having the oil changed yet is harming this but I am still in th 40% range with oil life and the dealer said to change it around 10%. Any help from CTS owners with this engine will be appreciated. I have searched the forums without finding a definite answer. My father is a mechanic for over 30 years so there is nothing mechanical that we have seen or felt wrong. Let me know what you guys think. Thanks alot.
 
#25 ·
Re: Gas Mileage Low??

Where do you drive? City or highway? I pay more attention to the avg mileage than the estimated range, and even more to the math I do in my head when I fill up. I noticed I get about 28-29mpg if I relax and cruise on the hwy, once I got 32mpg and the odometer/fillup math seems to support it. The next time you go for a decent hwy drive reset the average, drive consistently and then check the average as you get off the highway.

You may also want to check your gas source, maybe switching to a higher grade of fuel for a tank to see if that makes a difference.
 
#27 ·
Re: Gas Mileage Low??

I'll bet you've had a stretch of colder than normal weather. When the car hasn't warmed up and is still in open loop the mixture is determined from a lookup table rather than feedback. The car can really suck up the gas during these conditions.
 
#31 ·
Re: Gas Mileage Low??

Thanks for all the responses. I do mainly all city driving. The average mpg has not been reset in some time and it reads in the 11mpg range. No codes have been set off. I am bringing it in to the dealer friday for the rearend recall, my first service, and I will explain the problem to them. I do use regular gas which I thought I could use but I will try a higher grade to see what happens
 
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