: Sudden Increase in Oil Consumption 2003 DHS

10-18-13, 10:31 AM
I have a 2003 Deville DHS with 84000 miles on it. It has always (IMO) used a lot of oil, about a quart per 1000. But this time, at 925 miles since the last oil change, the oil light came on and it took two quarts to bring it back to the full mark. This is concerning. There is no smoke and no leaks. What might be happening? Is oil consumption a known problem with this engine?

10-18-13, 12:08 PM
Some Northstars in this forum have been known to use a quart of oil - in your case, 5W-30 - in 600 miles. Unacceptable but true. GM's stated acceptable "target" for the engine is 1 quart in 2,000 miles.

With no noticed leak or smoke problems, you might want to read the oil consumption and related articles way up ^^^ (top black bar) in Cadillac Technical Archive - and the article titled "Occasional full throttle operation is good ......." in the Archive also.

10-18-13, 02:48 PM
Northstar Performance is possibly working on a solution on this subject

10-18-13, 09:48 PM
A qt per 1000 is a lot, but I think GM actually considers a qt per 800 acceptable.

That said, follow Sub's advice. Then take it out and drive it like you stole it.

10-19-13, 09:45 AM
That was some fascinating reading. I will be on the freeway today with intent to evade fictitious law enforcement rallying for my immediate arrest. I'll leave 'em in a cloud of carbon dust and hope I see my oil consumption respond positively. Thanks for the help guys.

10-19-13, 03:47 PM
Remember, speed is not the important factor here. It's high RPM and a nice long deceleration. Both accomplished by the use of 2nd gear. If necessary, you could accomplish the same thing within the posted speed limit.

10-19-13, 04:28 PM
yep .......... The idea is to load the engine to max power in 1st and 2nd gear, and just before the shift to 3rd you flip your foot off the gas and let the engine brake the car to less than 20 mph - forced deceleration. You do the whole procedure with the shift stick in 1 or 2 - the transmission WILL NOT let you break anything - you can go to vehicle speed limiter cutoff with the stick in 1 - but you'll need to have the gas pedal smashed to the floor the whole time.

Those numbers on the shift stick mean "This is my preferred gear" and the engine/transmission will stay in that gear until safe limits approach, then the drivetrain will shift up or down, depending on whether you want acceleration or deceleration - your gas pedal foot.

The OP's DHS is probably speed limited to 112 or 118 mph - determined by the speed rating of the original tire - on the door sticker.

10-19-13, 08:11 PM
The OP's DHS is probably speed limited to 112 or 118 mph - determined by the speed rating of the original tire - on the door sticker.
112. I can personally vouch for that.

10-20-13, 12:21 PM
We are in the Bay Area right now and with three hours on the freeway yesterday, I only had one or two opportunities to hit 6000 due to heavy traffic. I would have had better luck if I had known I could do the same thing in 1st gear. Will go out try that today which will be much easier to do.

10-20-13, 01:21 PM
It will be hard to do in 1st. 1st gear will wind up to redline and shift before you know it and then at such a low speed, the decel will be short. It's gonna be hard to accomplish in the Bay Area.

10-20-13, 02:11 PM
Haven't gone out yet but I was wondering about how I was going to handle the quick to redline issue. And now I am not clear on where the primary benefit is; the acceleration to redline, reaching redline, or the decal from redline. If for example it is the decal, then finding a long downhill stretch would be best. What am I truly shooting for here?

10-20-13, 03:02 PM
All of the above.

Maximum power acceleration loads the pistons and rings to the max; forced decel raises manifold vacuum to the max, unloading the piston rings which rotate in their grooves, thus shedding carbon and (hopefully) regaining some sealing ability. (These are low-tension rings, so any help is beneficial.) FWIW, forced or extended decel in these engines shuts off the fuel injectors so there's NO fuel used under the decel operation.

If you can pull it off, put the stick in 1, make sure that all traffic is clear, then from a rolling start stick your foot through the firewall and leave it there. The car will accelerate to redline, shift to 2nd, and continue accelerating in 2nd. At the speed limit or 6,000 rpm (in your car that's well over 80 mph, so let your conscience be your guide) flip your foot off the pedal and let the engine decel the car to <20 mph.

Lots of black smoke on the first try ?? Do it again.

Did you ever go up ^^^ to the top black bar - Cadillac Technical Archive - and read the article "Occasional full throttle operation is good ........" ??? There's other necessary info for you there, too.

Just as an aside, a VIN Y car taken to engine redline in a gear (no speed limiter) would hit close to 45 in 1st, 88 in 2nd, and well over 130 in 3rd. (VIN Y = 3.11:1 final drive - economy cruise gearing. VIN 9 = 3.71:1 final drive - performance gearing) Our 4T80E transmission uses 3rd gear as 'top gear' - the 1.00:1 gear. 4th is a 0.68:1 overdrive.