View Full Version : Another (slightly different) Northstar oil consumption question.....

02-09-12, 04:10 PM
Background......2001 STS, with 163,000 miles. Purchased in 2007, when it had 51K miles. Oil consumption was in the 1200mile/quart range, dropped to less than 500 miles a quart, due to the prototypical "upper/lower shortblock seam" leak. Lived with it, knew I'd have to deal with a head gasket problem eventually. (Put a "Pratt and Whitney-Dependable Engines" logo on it, as I'm used to P&W radials and jets throwing oil).

Head gasket went blooey last February, @ 133,000 miles. Had my local Caddy dealer do the "head stud" mod, also fixed the upper/lower shortblock leak, among other major/minor items. Car has been running fine (well, no drivetrain related issues), no codes, no driveability problems, oil consumption was down to somewhere between 1200-1500 miles/quart.. until it turned cold in December. Oil consumption now back down to 450 miles/quart. Put the car up on stands last night, no leaks/stains evident anywhere.....dry as a bone.

So.......anyone got any ideas where it's going? Only clue/anomaly evident is that it seems to put a lot of BLACK smoke out during hard acceleration.....as in Cummins diesel quantities. It's always done it some, but it always looked more like an excessively rich fuel calibration during acceleration to me.

Valve stem seals on the intake valves? If so, can they be changed without pulling the intake cams, and/or pulling the timing chain and gears? Also, I understand this engine doesn't have a PCV valve

02-09-12, 04:50 PM
Black smoke on startup ?? Fuel pressure regulator. Under the beauty cover, rear run of the fuel rail. Start the engine, let it idle. Pull the vacuum connector off the FPR nipple - ANY gas ?? If so, change the FPR.

There's a test port on the fuel rail, covered by a black plastic cap. Same as a tire valve stem. Bleed off the rail, pull the hairpin clip off the FPR and lift it out - make sure the lower O- ring comes with it. Oil the O-rings on the new FPR with engine oil, pres it in and install the clip and vacuum line. Key ON for 5 seconds, OFF for 15. Do this 3 times to prime the fuel rail and injectors.

(Valve stem seals have nothing to do with the winter fuel consumption - that's in the oil consumption territory, but burning engine oil is blue smoke. Have you run the dog snot out of the car lately ?? Sedentary Northstars burn a lot of oil - drive it like you stole it. Go up ^^^ to the black bar and study the entire Cadillac Technical Archive, especially the articles on Northstar oil consumption and "Occasional full throttle operation is good .........")

You MAY have a PCV rattle valve, under the beauty cover, in the right (rear) cam cover. Sometime in 2001 they went to a fixed orifice that does NOT easily come out of the cam cover. PCV dirty air goes into the passenger end (front) of the intake manifold tunnel. Clean air comes from the atmospheric side of the throttlebody casting into the left (front) cam cover. Valve stem seals - an unholy bitch to replace. Essentially calls for a complete top overhaul, heads off the engine.

02-09-12, 06:00 PM
No problems with "fuel consumption".......(well, other than I wish this thing got 35mpg.....:D.......) For what kind/size of car it is, and as fast as I drive it, I really can't complain. (21-23 mpg highway @80-85mph, depending on the wind. Have occasionally seen 25mpg plus when driving it like grandma)

I'm driving it 70 miles to work/day (each way), 4-6 days/week, at 75-85mph. I hammer it pretty good out of the toll gates, traffic and cops permitting. No, it doesn't sit around much. Probably why the rest of the car runs/works as good as it does.

Haven't seen/noticed black smoke on startup, only when accelerating hard out of a tollgate. Exhaust tips have some black soot, but don't see any oil reside on them, or on the back of the car. Like you say, if it was burning oil, I'd expect to see blue smoke.

02-10-12, 11:33 AM
Curious, because the tips on my car are polished stainless steel - they're as clean today as they were 5 years ago when I installed the exhaust system, and my gas mileage is close to yours (24.7 long term, 70 mph) - but never a hint of black smoke on WOT acceleration. My engine goes more than 4,500 miles per quart and it has the PCV fixed orifice.

Mark D
02-11-12, 02:15 PM
A possibility, but really slim possibility... It could, but not easily, be a leaky injector or injectors that allow too much fuel through during idle at the toll booth. It clears in the form of black smoke as you accelerate out of there.
You might want to do a simple test to see if this is a possibility. find a fuel pressure gauge somewhere if you don't have one. Attach it to the test fitting on the far end of the fuel rail, as mentioned above. Turn the key on to let the pump run, then off. Do this a couple times. Read the pressure on the gauge. Watch the gauge. If it drops more than a needle width or so, there is probably at least one injector leaking.
The only other thought that occurs to me is the PCM commanding a very rich mixture during idle. But that should be accompanied by some sort of DTC being set, and you don't mention the SES light being on. Still, you might want to display your codes and see if you have anything interesting going on. Yet, anything related to engine performance should light the SES.
Mark D.

02-17-12, 04:38 PM
No - the black smoke is blowby from the PCV system that has collected in the intake manifold - it gets sucked out of the intake manifold during WOT runs - usually only one or two of them - then you won't see that black smoke again unless you drive conservatively for a week or two, and then get on it hard again. Your rings are probably worn some, increasing the blowby. Also, if you drive it hard all the time, you will not see that black smoke at all -that's why Sub never sees it LOL!

02-17-12, 05:03 PM
how did this thread turn from oil consumption to an mpg/fpr thread?

02-17-12, 05:54 PM
how did this thread turn from oil consumption to an mpg/fpr thread?

Black exhaust smoke questions.


-that's why Sub never sees it LOL!

Not quite - My engine uses less than a quart of oil in 4,500 miles - Post # 4. The inside of my intake manifold and throttlebody are perfectly clean.

It would take a LOT of oil pooled in the lower log of the OP's 2001 intake manifold to allow it to be sucked into an intake runner - and the causative blowby would be evident with the engine idling with the oil filler cap off - you would see vapor blowing [not drifting] out the filler neck.

EDIT: Blowby. Start the engine with the beauty cover off. Pull and plug the PCV clean air line grommet at the left (front) cam cover - don't plug the line, plug the cover. Remove the oil filler cap and place the palm of a hand over the opening. Does the PCV system very gradually pull a vacuum on your hand ???

04-14-12, 01:22 PM
I'm checking in because I have a similar problem with a 2001 Deville that i just bought. Seams to be using way too much oil. Its has 169,000 on the motor. Did you find your problem?


04-14-12, 03:15 PM
I'm checking in because I have a similar problem with a 2001 Deville that i just bought. Seams to be using way too much oil. Its has 169,000 on the motor. Did you find your problem?


Welcome Aboard !!!.......:highfive:

Go way up ^^^ in the black bar and study the entire Cadillac Technical Archive. There are articles on oil consumption, engine exercise, and oil life monitor in there.

GM's Northstar engine guidelines have been revised to accept about a quart every 2,000 miles as 'normal' consumption. If your car is a sedentary city driver, it may be time to work out the engine. All covered in the Archive ^^^.

Douglass Harroun
04-16-12, 10:13 PM
Did you take the pistons out with the last repair? If not, I bet you have gummed up / stuck oil rings