Last post on Jun 03, 2012 at 3:22 PM
You are in the Cadillac DeVille
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Cadillac DeVille, Sedan
#3 of 6 Re: Remove Carbon from Northstar engine [bolivar]
Jun 11, 2009 (8:59 pm)
You know as well as I. No dealer is going to F with a '97 model. I was hoping y'all smart guys had a solution to do it myself or take to my trusted/non dealer to do the job. I'm old and not likely to buy a new car. I like this car and don't want to blow it up or wreck it driving recklessly. It really runs very well, gets about 26mpg uses the first quart of oil immediatly and the second quart every 1000 mi or so. I normally run it a quart low.
#4 of 6 Re: Remove Carbon from Northstar engine [swwjr05]
Jun 12, 2009 (12:18 am)
So what you have is oil usage.
1000 miles / 26mpg = 38 gallons gas X $3.00/gal = $114 for gas.
In this same 1000 miles you use 1 qt oil = $4.00.
Spend $114 for gas and $4.00 for oil. Oil is cheap. Just keep pouring it in and otherwise ignore the problem.
It 'immediately uses a quart'. My guess - you are topping an oil change up to the upper mark on the dipstick. Most Northstar dipsticks are badly marked. The motor takes 7 1/2 quarts with a filter. Put this amount in, no more. It will show below the upper mark, but at 7 1/2 quarts, it is full. When checking the oil, keep it at this level, not at the upper mark.
If you top it up, you can get about an unneeded 1/2 quart in to get to top of dipstick mark. The motor will quickly suck the extra 1/2 quart out thru the PCV valve route. If you are attempting to keep the oil level at the upper mark, this is some of your oil usage.
Sorry, but the only 'cure' I've heard about, rather than a motor rebuild to replace the rings, is WOT or the factory ring degunking in the TSB I discussed in the earlier message.
Driving a Northstar around in 'Granny mode' will cause the rings to accumulate carbon and stick. The stuck rings cause oil usage. And, driving the car at 70mph on the expressway, will NOT keep the rings from sticking. At this speed the motor is still just loafing along. You may also get carbon knock. This is when a piece of the carbon breaks off and sticks to the top of the piston. It then hits the head and sounds just like a stuck lifter in a Chevy small block.
Stuck rings (oil usage) and carbon knock come from easy driving and using premium gas. Premium gas doesn't really run better, it actually is more resistant to firing. This keeps the motor from pinging. But at low rpm's this resistance leads to carbon and stuck rings.
A Northstar is a high performance motor and needs to be run to 6000rpm a few times each month. Several times. Take it out to an area with low traffic. No need to accelerate from a dead stop, just keep the accelerator floored from first gear and let it make two upshifts. This will mean you are going about 80mph, which everyone drives on any rural interstate. Do this two or three times. If the motor or tranny breaks, it was going to break in any case in the next 1000 miles. Northstar motors don't break, other than blowing head gaskets, and trannys don't break, they have sensors fail. WOT usually won't trigger either of these problems.
I've got the full TSB description and will post it here if you want to attempt it yourself. It has the part number for the degunk 'kit', and I think you would not need the special machine. You could just pour the degunk in the cylinders and suck it out with a shop vacumn. But the procedure is long and messy, requires pulling all plugs, etc.
#5 of 6 Re: Remove Carbon from Northstar engine [swwjr05]
Jun 12, 2009 (11:08 am)
As the owner of as '99 STS that carboned up, and was cleaned by the dealer, under warranty, I can tell you that WOT works best!
After a few WOT runs, my oil consumption went down. I was burning a quart about every 2000 to 2500 miles. After WOT, I would get another 1000 more miles per quart.
The Northstar is a performance engine and needs to be pushed every once in a while. As another senior citizen, I can tell you that we do too! Get in there and push that pedal down, you'll love it!
#6 of 6 Carbon buildup
Jun 03, 2012 (3:22 pm)
O.K. Guys this one is real easy.I am a master mechanic of 32 years and the old "tricks" still work best. Get a small cap of water bring the RPMs up to around 2500 slowley pour the water in to the intake the motor will bog down a bit if done right increase throtle to keep from stalling.only use about 4 OZ of water after this the motor will run perfect.And I do this to my customers cars without charge.A little know how goes a long way, Hope this helps some of you out there.