De-carbonization on Northstar

[Joe Bisbee]

My 2001 DTS has been burning oil. . .Talked to a mechanic who said the carbon build up is on going issue and that dealers have technical service bulletins that is on going. . .Anybody else had this situation. . .Car has on 27K on it

[Porter 21919]

I have read they need to be driven (accelerated) hard occasionally to decarbonize/prevent sticky rings. They are built for it.

http://www.alldata.com/TSB/08/010822FR.html

[David #19063]

All Northstars seem to use quite a bit of oil.  I think even in the glove box manual, it says that it can be as high as 1 QT every 1000 miles, depending on habits.  I have had some cars that used no oil in 3000 miles.  Our 96 Concours, the pre-DTS uses 1-2 QTs every 300 miles.

If yours uses about that, there really is not an issue.  

What gas octane do you use?

Burning premium gas will keep your valves cleaner as well and give you better performance.  The engine can adjust and run on low octane or adjust and run on premium.  You do get better performance from the premium as it is designed to adjust for premium.

David

[Rusty Shepherd CLC 6397]

Did you mean to say 1 or 2 qts every 300 or 3000 miles? If its every 300 miles, Ill try to stay out from behind you on the road. I have had two Northstar cars, both bought new..one used a quart every 1,500-1,800 miles, the other one about every 1,200 to 1,500.  The 4.9 I had before them used some oil, too, but not as much, usually needing a quart about the time of the 3,000 mile change.

[David #19063]

Rusty,

Yes, you are correct, 1-2 Qts every 3000 miles not 300.

Now, back in the late 80s, I did have a friend in college whos worn our 69 Riviera GS 430-4 blue smoke oil burner would use a qt ever 300 miles...hes just wait until the oil light came on and put in 3 qts.  The car was missing the oil dipstick and we never knew how much oil was in it.  Lucky SOB...LOL!  Most cars are toast by the time the oil light comes on.  And the car would still hang with a 5.0 Mustange GT in th 1/4 mile!

Would have like to see that car brand new!  The Riv GS came stock with a 3.42 limited slip rear.

David

[Matt Harwood]

What gas octane do you use?

Burning premium gas will keep your valves cleaner as well and give you better performance.  The engine can adjust and run on low octane or adjust and run on premium.  You do get better performance from the premium as it is designed to adjust for premium.

David

No, no, no! This is absolutely not true. Premium fuel does not have additional cleaners in it and will not affect performance unless the vehicle is specifically designed to use high-octane fuel. I seem to recall that recent Northstar motors in the DeVilles were designed to run on regular fuel. Adding high-octane fuel will not magically make more horsepower as if the car has the ability to sense the octane and tune itself accordingly. If it doesnt ping on regular, high-octane is just throwing your money away. If it is rated at 300 horsepower on regular, 300 horsepower is all youll ever get out of it no matter what kind of fuel you put in it. Octane IS NOT A MAGICAL HORSEPOWER GENERATOR OR INTERNAL ENGINE CLEANER.

This is exactly the kind of myth that gets spread about high-octane fuel--it is 100percent incorrect. Sorry, David, I dont mean to single you out, but these wives tales about octane persist because of posts like this.

Heres more (Im pretty sure Ive posted this here before):

http://www.harwoodperformance.bizland.com/1941buick/Editorial_13.htm
--
Matt Harwood
Cleveland, OH
My 1941 Buick Century restoration:
http://www.harwoodperformance.bizland.com/1941buick/index.html

[Lars Kneller 8246]

My new 05 STS V-8 states in the manual that premium is prefered for "maximum engine power".  It will run on regular and midgrade, but the engine computer adjusts the timing (valves? ignition? maybe both) and lower power output results.  I do wholeheartedly agree if the engine is made for regular (like my 77 Eldo) it provides no benefit to put anything else in it.  I do run premium in the STS.  I want to get all the horsepower I paid for!

On another subject my Northstar holds 8 quarts of oil, and comes from the factory with Mobil 1 in it, and this is the factory recommended oil.  Is this true of older Northstars?

[Matt Harwood]

Yes, if it is designed for premium and the manufacturer recommends premium, then your engine will run better than it would on regular where the computer MAY retard the timing.

A lot of folks think that high octane fuel somehow burns hotter and makes more horsepower--NOT TRUE! It only lets an engine run at its potential. If its already running at its full potential with regular, premium will do nothing but make your wallet lighter...

[Michael Stamps 19507]

Lars you can do as Densie did on hers and tune the timing for high test.  She gets better gas mileage and performance.

Stampie

[Kevin Parkinson 20216]

I changed the oil on my 99 Deville a few weeks ago and it took 8 quarts.

[Lars Kneller 8246]

Can you give the details on what to do?  Thanks.

[Michael Stamps 19507]

Well first I would route the vacuum advance straight to manifold.  That gives you advance at idle and around town driving for better mpg, more performance, and cooler running engine.  You can get an adjustable advance for these engines around $25.  You can set it to be all in pretty low.  You can also bump up your inital timing.  10 or so should work.  If the it fights the starter then back it down 2 degrees and you should be fine.  Denise might be able to add more.

Stampie

[Bret Scott (CLC 21765)]

Hi, Joe-

Hunting around, I found partial text from the technical service bullitin that deals with this issue (provided below).  An interesting point often missed but covered in the bullitin is that the Northstar motor distick design may lead to overfilling the motor.  Northstars of your vintage take 7- 1/2 quarts, while filling the oil to the maximum mark on the dipstick requires 8 quarts.  This extra oil is burned off, and may give an indication of higher-than-normal oil consumption.

Regards,

Bret


Technical service bullitin:

Higher Than Expected Oil Consumption (Clean Piston Rings) #02-06-01-009C - (10/23/2003)
Higher than Expected Oil Consumption (Clean Piston Rings)
 
1996-2000 Cadillac Concours
1996-2002 Cadillac Eldorado
1996-2003 Cadillac DeVille, Seville
 
with 4.6L Engine (VINs Y, 9 -- RPOs LD8, L37)
 
This bulletin is being revised to add parts information. Please discard Corporate Bulletin Number 02-06-01-009B (Section 06 - Engine).
 
VIN Breakpoints
Model Year * Model * VIN Breakpoint
 
1996-2002 * All Above * All
 
2003 * DeVille * Prior to 3U213641
 
2003 * Seville * Prior to 3U215818
 
Condition
Some customers may comment on higher than expected oil consumption. The typical customer with this condition comments on consumption in the range of 0.946L (1 qt) of oil used in 1600-2250 km (1000-1400 mi) of operation. The oil consumption rate and possible oil consumption areas, as per Corporate Bulletin #01-06-01-011 dated March, 2001, should be verified prior to performing the ring cleaning procedure below. The standard for acceptable oil economy and the method for determining oil economy are outlined in Corporate Bulletin #01-06-01-011.
 
The following text is referenced from Corporate Bulletin #01-06-01-011 for your convenience.
 
Oil Consumption:
 
The accepted rate of oil consumption for engines used in the vehicles referenced is 0.946L (1 qt) in 3200 km (2000 mi). This rate only applies to personal use vehicles, under warranty, maintained in accordance with the appropriate maintenance schedule, with less than 58,000 km (36,000 mi), or 80,450 km (50,000 mi) for Cadillac, driven at legal speeds in an unloaded (for trucks) condition.
 
Cause
Although there are several reasons for less than expected oil economy described in Corporate Bulletin #01-06-01-011, one area not covered is reduced sealing ability of the rings. Through normal usage, combustion chamber deposits may build up to the point that the movement of the rings could become restricted and prevent the rings from wiping all of the oil off the cylinder walls and allowing it to be burned in the combustion process.
 
Correction
A new ring cleaning process has been developed to restore the function of the rings. Once the possible oil consumption areas in Corporate Bulletin #01-06-01-011 have been eliminated, this cleaning process should be performed. If the oil economy has not improved to 0.946L (1 qt) in 3200 km (2000 mi) after cleaning, it may be necessary to replace the piston rings. Be sure to install the second compression ring notch side down. If the vehicle is a 2000 to 2003 with an oil consumption concern with less than 25,000 miles on the vehicle, then skip the cleaning process and install the new rings.
 
Important
It is critical in this cleaning process that the piston and ring cleaner remain in the cylinders for a minimum of two hours to fully clean the components. The cleaner solution must be removed before three hours. Additional soak time does not increase the effectiveness of this process. If solution with the dissolved deposits remains in the cylinder too long, it will soak back into the rings and cause them to stick again. If this happens, the oil economy will be reduced even further.
 
An oil economy test should be performed after the cleaning process is completed. Before starting this test, the full oil level on the dip stick should be noted and shown to the customer. The correct oil fill is 7.1 L (7 ½ qts) with a filter. The dipstick should not be read for at least 15 minutes after the engine has been shut off for an accurate reading. Typically, the oil level shown on the dipstick is in the second or third section above the add mark. If the indicated oil level is at the MAX mark, there is approximately 0.47 L (½ qt) too much in the system and it will be scavenged by the PCV system quickly. When performing this test, the most accurate results may be obtained by having the customer drive the vehicle until the CHECK OIL LEVEL message appears and then returning the vehicle to the dealership to determine the oil economy. No damage will be done to the engine by operating it until the Check Engine Oil Level message is displayed. There is 4.7 L (5 qts) of oil still in the system.
 
Field feedback has indicated that vehicles that have been operating at a high consumption rate (0.946L (1 quart) of oil in 1600 km (1000 mi) or less) for greater than 32,000 km (20,000 mi) may need a second application of the piston and ring cleaner to adequately clean the rings. If a second application of piston and ring cleaner is necessary, it can be done immediately after vacuuming out the first application.

[Chip Hodges, CLC #20536]

I am sure glad I came across this discussion on de-carbonization of the Northstar.  

My 2001 De Ville has developed an engine knock at idle, and I have been pretty concerned about it.  The dealer told me just today that it is caused by carbon buildup, and has scheduled the car to go in next week to have the engine pumped with some type of chemical, and then flushed out.  The service manager claims this will take care of the problem, but I am still somewhat skeptical.

Has anyone out there had a problem with engine knock due to carbon buildup?  Yes, I do run it on regular, perhaps I should switch to premium.

Chip

[Porter 21919]

Would like to hear your thoughts.

TIA,

Porter

[Porter 21919]

My 90 & 93 ETC required premium or they would ping.

All the old high compression engines required high octane gas.

I used to run premium gas, octane boost and lead additive in my 66 327 Vette with ignition advanced two degrees.

Maximum performance and Mustang destruction.

LOL,

Porter

[David #19063]

Hello Chip,

I hope that dealer is doing this carbon removal for free...call them and find out.  Dont let them talk you into paying for anything.

If not, skip it for now and start using premium...all the time.

Also, some dealerships and shops have a product call B&G 44K.  It is a fuel additive.  Cost about $13-15/can.  Call around and find some...right away.

Put one in prior to a premium tank fill up.  I think B&G only recommends you do this once or twice between oil changes.  This is the best stuff ever.  It does wonders for valves and injectors.  And I have used it in my older carb cars as well.

Please let us know your results.

David

[Chip Hodges, CLC #20536]

David,

Thanks for the advice about the B&G 44K.  I will try to locate some tomorrow.  Good timing, as the car will need gas tomorrow. I will of course use premium this time, and in the future.

Fortunately the dealer had already told me that they would not be charging me for the de-carbonization procedure. I made it clear to them that I did not feel that this falls under the umbrella of routine maintenance, as the problem appears to be due to a design flaw with this type of engine.

I am concerned about one thing.  Someone in this discussion of de-carbonization stated that the de-carbonization chemical brew should not remain in the engine for more than three hours, but the service manager told me that they would be leaving it in the engine overnight prior to flushing it out.  I hope they know what they are doing.

I will let you know next week how everything turns out.

Chip

[David #19063]

Chip,

You could always put off the decarb at the dealer until next week and see if a tank or two of premium and the 44K makes a difference by itself?

It may need the decarb after all this time, but at least this way, you would know for sure if it needed it.

How long will it take you to burn up a tankful of premium?  Can you do it within a couple three days?

Just a thought.

David

[Chip Hodges, CLC #20536]

I was thinking the same thing.  I will be making three trips into town between today and next Tuesday, which is when I have the appointment to take the car in.  I will nearly have used a full tank of premium and the 44K by that time.

I will listen for the engine knock on Monday evening, and if it has improved, I will postpone the de-carbonization until I have used a second tank of premium.

Chip