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Mileage STS/CTS


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What is the milage of the 3,6l CTS in highway driving (75mph)

I'm wondering because i will sell my STS and buy a 02-03 STS (with lower miles) or a -05 CTS

My STS has taken 10,8 liters/10km (18,65gallons/100miles?) counted of the latest 42000 miles.

What I hear it is a very little difference in highway mileage between STS and CTS and if it is I will continue to drive STS.

I have also heard that ethanol prices is decreasing in USA, has anyone tried to go on 85% ethanol in a Northstar engine? Or do you have to improve the compression and change the injectors to get it proper?



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With regard to the compression ratio, its already 10.3:1, quite high

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2002 Cadillac Seville 16 mpg city, 25 mpg highway; 14.7 L/100km City and 9.4 L/100km highway.

2005 CTS 3.6L auto also 14.7 L/100km City and 9.4L/100km highway.

In my real-world experience the 05 CTS 3.6L gets 3-4 mpg (15%) highway better mileage than the 96 Northstar STS I had. During the years that Cadillac produced the STS and SLS models together, they would submit the SLS for mileage estimates and confirm the STS by similarity. So the estimated mileage tends to match more closely to the SLS than the STS.

NOTE: the EPA has revised the older model estimates to match the current test methodology. For comparison, the 2005 CTS was rated 17/27, but now is rates 16/25 mpg city/highway.


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Thank you all for replay

I think I will get a "new" STS again. In Germany the prices goes down very quickly on STS.

New prices is about $100,000 here and you can get a 02-03 with 30,000 miles for $25,000

The CTS seems to be more popular and are more expensive as a second hand car. The prices will be about the same as for STS.

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My owner's manual and the 1997 FSM says that all bets are off if your fuel has more that 15% ethanol. Anyone try E85 in a 1995-1997 Northstar?

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My owner's manual and the 1997 FSM says that all bets are off if your fuel has more that 15% ethanol. Anyone try E85 in a 1995-1997 Northstar?

Maybe it's just me..... but I wouldn't even "CONSIDER" putting E85 in my Northstar. If I happened to be somewhere where I couldn't find ordinary gas and ran out... I would hitchhike...walk to a station...call road service.... SOMETHING..ANYTHING.. to keep from putting E85 in my Cadillac.

Heck, it don't even like the 10 percent crap we have in this area. On some of my trips, I have found a couple of stations... out in the middle of nowhere, where I think I got REAL GAS with no ethanol.

The car ran so much better and got fantastic gas mileage... but just till I put gas in it again. Dang it. Then it was back to normal.

Just my opinion.

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My 1999 STS @ 72 -73 mph gets 25.5 mpg on a bad day (which would include at least 1 WOT) and 27.5 on a good day.

Don't even think about using E85 in a Northstar, they were not designed for it. And IF you do find a car that IS designed to use E85 (they will be clearly marked as FlexFuel) expect about a 20% REDUCTION in fuel economy! This would be the quickest way to turn an economy car into a gas guzzler that I can think of!

Never underestimate the amount of a persons greed.

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