I have a 97 STS, I purchased it with 19K, currently pushing 50K, I noticed early on that it would burn a lot of oil, about the same you are experiencing. My dealer told me to expect it to be down one to two quarts during oil changes. Other than that the car is great, I also have an older Seville pushing 200K it also has been a great car.
I have recently purchased a '97 STS with 49K miles. The car has tons of power and is reasonably comfortable. I was warned ahead of time about the oil consumption so I knew what to expect. It definitely does use it's share of oil. It does not appear to be blowing blue smoke nor is it marking the rear (plastic) bumper. It loves fuel. There is a big difference in consumption between 70 MPH and 80 MPH. The biggest complaint is with the lack of interior storage space. My old Bonneville SSE has much more storage space than this car, which does not say much for Cadillac's "best" model. It is a beautiful car and turns many heads. The body-style is a classic. I was also warned (by a friend that works for GM) that there is a strange "wiggle" that comes from the rear of the car going over larger bumps. I must say that I have noticed it, but think it is not much to be concerned about. I will say this, though, if the Germans could get their large cars priced more competitively than Caddy better get it's "stuff" together.
I purchased a 1997 Cadillac STS on a ‘lease turn back’ in 1999. The car had 32K miles at the time. Shortly before the first oil change, I noticed a very high oil consumption rate - 2 to 3 quarts low - and inquired at the dealership. They claimed this was normal. However, when I discussed the matter with one of the mechanics, he told me this was not normal, and that if I pushed the issue, GM would fix the problem. I logged oil consumption and returned to the dealership, whereupon the service writer miraculously came up with an official “GM Oil Consumption Test” form. It took another few months of logging oil changes and consumption, and GM finally agreed to re-grind the cylinders and install new rings. The mechanic had said that this would be the first thing they tried. He also said that the oil consumption would actually get worse – the Northstar engine has such tight tolerances that they had found a re-work of this nature simply does not work. All True. Another 3 to 4 months and many thousands of miles of another “Oil Consumption Test” and GM finally agreed to put in a new engine under warranty. Since then – roughly 40K miles – no oil loss whatsoever. In short, the oil consumption should not be this high (at least in the 97 model year) and GM knows it.
1999 De ville- same engine as Seville- I just went through the oil consumption bit with the dealer. Car has just 26,000 miles and also uses 1 quart in a little over 1,00 miles.
Man, does this oil consumption thing tick me off. I bought the car with 3,000 miles on it, (it was a program car in the 1996 Summer Olympics.) Got a great deal - $51,000 list and paid $37,000 for it. In 130,000 miles, I've only replaced a handful of things; a power window motor, an A/C compressor, the blower motor, and EGR valve and an O2 sensor. I'd say that's pretty reasonable for seven years of hard use, especially when compared to the service records of American cars produced in the 70's.
The oil consumption, however, has been awful. I guess GM knew all about this - that's why it holds 7.5 quarts. I, like everyone else, went to my dealer in awe of the perpetual, "check oil level," message. They said that this was, "...within specs." I've NEVER seen ANY car use oil like this. O.K. SO, I can afford a few quarts of oil and I do keep spare oil in the trunk, (like I used to with my old junkers as a teenager.) The one thing that really stinks, however, is the, "James Bond smoke screen," that I put out whenever I really step on it. Its particularly bad if I'm near the end of an oil change cycle, (which for me is every 3,500 miles.)
Cadillac Service bulletin 01-06-01-011 offers a ring cleaning procedure as an alternative to new rings or a new engine. GM cleaning kit Part Number 12378545 is a solvent that you squirt down the spark plug holes for a couple of hours. Then you suck the gunk out with Kent-Moore J-45076 induction/evacuation tool and change the oil. I haven't tried it - don't know how mileage affects the success rate.
I've also started to have a little trouble with the throttle body getting gummed up and the throttle sticking shut.
And yes, I agree with everyone else that there aren't any places to put anything in the car. When you get into much cheaper cars, there are little cubby holes everywhere, but in the STS, you travel light. The other thing that drives me nuts is the insanely long rear door panels. While the door panel is so long it hits virtually everything you park near, only half of the door panel exposes the seating area, so your rear seat occupants have a very small space, (especially for their feet,) to squeeze in and out of. The side, rear-view mirrors are also so small, they're fairly useless.
All of that being said; I'd buy the car again. It still turns heads and will pass almost anything on the road. The 11 speaker Bose system is a joy to wring out when there's nobody else in the car.
January 9, 2003
Cadillac STS 1999 purchased new now has only 16,000 miles. Uses 2+ quarts between 3,000/m oil changes. Dealer says "that's normal", but no mention of corrective possibilities. Dealer mentioned car uses less oil if driven hard. "Check the internet to see if I'm not correct" OK, did that. Bummer. No evidence of leakage or exhaust smoke. Surprised at the the number of engine replacements in these comments. Think I'll dump it before the warranty gives out.
I bought a '95 De ville Concourse (same high HP motor) way back when with 40,000 miles on the clock. Since day one, I noticed the crazy oil consumption rate. I took it to the dealer-same story, normal for the car. I almost fainted! As a mechanic, I crawled all over the thing looking for leaks or blue smoke plumes. Nothing. For the past three months I have been putting regular in her tank, and, she actually does go to 3500 miles with only a 3/4 quart loss. Go figure.
I own a 98 DeVille. One quart every 1000M. Recently switched to Quaker Synthetic. See if that makes a difference. Also, can anyone really verify that using regular gas helps the oil consumption problem and why would that be?
Allow me to add this sorry bunch. I too purchased a used 97 STS. After about a year, I was having problems with oil consumption - it eventually got as bad as 7 Liters between oil changes. At first, the dealer monitored it - said it was normal. Ultimately they agreed it was excessive and tore down the engine. It was beyond repair - piston slap, and bores out of round. Since then, the replacement engine too is burning oil. Lessons Learned: 1. Do not fall for the de-carb procedure - it makes it worst and you have thrown your money down the oil pan 2. If enough of us gripe, GM may come to its senses and realize it has turned off its most lucrative buyers - I'm in for a class-action suit 3. Fill'er up and check the gas.