Northstar Engines and System Technical Discussion Discussion, Northstar Oil Consumption in Cadillac Engine Technical Discussion; I have a 99 STS with 60,000 miles. The oil consumption seems high to me, over one quart per 3,000 ...
One quart in 3000 miles is well within spec. The actual tolerance limit is one quart per 1000 miles. This is due to the aggressive and deep hatch pattern on the cylinder walls, to promote good high speed oiling. Downside is increased consumption over a "normal" design. Upside is you'll probably never have to have your Northstar oversized due to cylinder wall wear.
Some engines use more than others -- this is due to the depth of the hatch lines in the cylinders. New stones are installed after every so many engines have passed through the machine. There will inherantly be a variance between the first engine on a set of stones (deep hatching, very good oiling, most consumption) and the last engine on a set of stones (moderate hatching, still good oiling, least consumption). Sounds like your engine was towards the middle of the pack. Mine is too -- I use a quart about every 2000-3000 miles. I also run the snot out of it regularly -- and that adds to the consumption as well (makes sense -- more rpm = more oil consumed).
That's odd. How do you drive the car? Is it mostly at light throttle (just cruising around), or do you run it up to redline a few times a week? The rings like higher speeds to keep lubricated. It's conceivable for the rings to stick if the engine is constantly driven below 2000 rpm or something like that.
I'd suggest doing some 20-80 mph full throttle runs to blow all the junk out of the engine. You'll probably notice a lot of smoke out of the tailpipes, but this is good -- you're getting any carbon/caked oil out, and making room for good lubrication again. This may unstick the rings, if they are indeed stuck.
Then again, 1 qt/3000 miles is a pretty average-to-good rate for a Northstar -- I wouldn't do anything other than doing a few full throttle runs to satisfy my curiousity. Other than that, you probably have nothing to worry about.
George, has your leak been properly diagnosed? Many times, if it's a bad leak, it's something other than the case-half seal, like an oil filter adapter seal or oil cooler o-rings (for the 1995 and earlier cars). Has your dealership put the dye into the oil to see exactly where the leak is? The case-half leak usually does not leak but a drip each day or so. If it's a puddle each night, it's probably something else. Not saying that it can't be your case-half seal, but it may also be something else, something much cheaper and easier to replace.
Just a few tidbits from good old me. The acual capacity of a northstar is 7 quarts. 6 crankcase and 1 in the filter. The oil consumption that you are talking about is very normal, northstar had alot of problems in the early stages with real oil consumption 2-4 quarts in 3000 miles or worse. If your burning a little oil then the engine is running correctly. If you are getting the oil indication from the OBD2 on your display then you may have a bigger problem. In OBD2 your "check oil level" indication will only come on when the oil gets at least 2 quarts low. If you are recieving this then you may well have a bigger problem. The biggest thing is make sure whoever does your oil change does it correctly. I've seen the jiffy lube type places only put 5 quarts in before. This is a common problem becasue who really looks at thier dipstick after an oil change, you may have lost 2 quarts by the minimum wage worker only doing half his job. Caddi dealerships are no different they pay better than minimum but still the oil change guys are not technitions. Just some food for thought take a look at the oil after it is changed, also look at your PCV valve. If its stuck then your crank case is not being ventilated properly, this may cause oil consumption problems by blowing back into the intake or air filter. All in all your problem is not really a problem as everyone else has stated. I hope this gives some perspective on the matter.
I've lowered the limit on searches so that we can type in 3 letters now. Sorry about that. I need to get that F.A.Q. section going... Would someone mind merging this topic with the other Northstar Oil thread?