: Cruising RPM Seems high



caddie07
05-24-13, 09:26 PM
This is the first Cadillac I have owned (or driven). My 07 STS seems to run high RPM when cruising. At 55-60 it hovers around 2000, and at 70-75 it's at 2500+. This has the 3.6 5 speed auto. All the gears seem to shift fine. I have had a couple bonnevilles (3.8) and the comparable RPMS were 300-500 lower. Mileage is no better than 20 on the highway. To me this seems a little high and not possible to get near the 27mpg that is claimed. Is it normal to run this high?

ddgm
05-24-13, 10:26 PM
The 3.6s have 3.42 rear ratios which is the lowest offered in our STS, the other 2 being 2.73 and 3.23. I'm not sure what the 2008+ 3.6s had. Maybe with the 45 H.P. increase they didn't need that low ratio. Being a Snowbird I was putting on 1500 miles one way driving to our winter home in Florida. I was looking into swapping the rear carrier but now that I have decided to fly, I don't think I'll bother. I was getting around 25 MPG on the trips at Interstate speeds ( 70-75 MPH). So I would say your RPMs seem to be right. I don't think any car gets the claimed mileage. These cars are heavy and mileage is very dependent on how they are driven. Have a good tuneup done, plugs, filters etc. and see what happens.

Doug

caddie07
05-24-13, 11:28 PM
Thanks for the response. We took a recent trip to Florida a couple months back and had the cruise set at 70-75 and were seeing about 20. The car only has 40,000 so not sure a tuneup would help much. It runs fine with the exception of when it shifts from 3rd to 4th on normal acceleration. It acts like a manual would when you shift too soon. Guess I am just used to my bonnie getting close to 28mpg. Was a little disappointed after we bought it only because of the mpg. Thought for sure I would get the 25 or close too. I keep my foot out of it too. I was just a little concerned about the rpm's. I am used to seeing the torque converter kick in and it drops again. Guess these don't do that.

EChas3
05-25-13, 12:42 AM
Doesn't the 2007 have the 6-speed trans or is that only on the V-8's? Most members with V6's report somewhat better mileage than that. The DIC may not be accurate. I know my 2006 underestimates fuel used.

My wife's 2007 V8 (2.73) once got 25 mpg @ 80 MPH (2krpm) on rock-hard Michelin Energy tires (a full tank calculated-not by DIC). Those tires bordered on dangerous and it now enjoys Blizzaks Nov-April and Conti DW's.

Ever change the air filter or clean the throttle-body? It's not too soon.

Ludacrisvp
05-25-13, 08:52 PM
Doesn't the 2007 have the 6-speed trans or is that only on the V-8's?

Correct, only the V8 got the 6spd in 07.

caddie07
05-25-13, 09:28 PM
So 2000 rpm at 55 seems fine then? I was using the dic for comparison. I do know I get a little over 300 per tank. Guess I was expecting better given a v6.

Ludacrisvp
05-25-13, 09:42 PM
So 2000 rpm at 55 seems fine then? I was using the dic for comparison. I do know I get a little over 300 per tank. Guess I was expecting better given a v6.

2000 RPM might be expected since it is the 5spd at 55mph. For comparison my AWD V8 6spd runs about 1800 at 65mph. My mileage is DIC reported between 16 and 21 at best for my mostly highway miles.

Guy.Seminerio
05-27-13, 05:58 PM
Correct, only the V8 got the 6spd in 07.
And the v6 picks up the 6 SPD in 08.

caddie07
05-27-13, 08:48 PM
So I am clear being this is my first Cadillac. 5th gear is overdrive. I won't feel or see another "shift" like when a torque converter kicks in like other vehicles.

EChas3
05-28-13, 03:05 PM
So I am clear being this is my first Cadillac. 5th gear is overdrive. I won't feel or see another "shift" like when a torque converter kicks in like other vehicles.

With the 5-speed, we have 5 distinct gears plus lock-up torque converter. All AWD's (V6 & V8) have the 3.23 gear. (I believe only the performance RWD get 3.42 gear.) I have the 18" wheels and 2,000 rpm is 60 MPH.

caddie07
05-29-13, 11:47 AM
I guess that's where I am getting confused. Other vehicles I can see the rpm go down when the torque converter kicks in. I guess these don't do that.

EChas3
05-29-13, 11:19 PM
Sure they do. Cruising down the road at 60, I'm turning 2,000 rpm. If I lightly press & let off the go pedal, not enough to downshift but enough to vary my speed, I'll see rpm's about 100 higher.

If you don't, maybe your trans clutch is weak and needs service.