Oil consumption

2006 CADILLAC CTS
79,000 MILES • 3.6L • V6
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GARY DREYER
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Even when it was new it used about a quart of oil in 5,000 miles. Now it is using a quart of oil in 1,000 miles. It doesn't smoke or leak, but there is black soot around the exhaust tips. The oil has been changed regularly and always used synthetic. Any idea what might be going on? And how much it would cost to fix? Would I be better off just adding a quart every 1,000 miles or spend the money to fix it? I do love this car and other than oil consumption it is in perfect shape and runs great.

Thanks, Gary D
Mar 29, 2017 at 1:31 PM
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CARADIODOC
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I wouldn't pursue anything yet until you switch to regular petroleum-based oil, unless the manufacturer requires synthetic. Any time there is a leak or a consumption problem, it seems to be worse with synthetic oil. Also, don't go 5,000 miles with regular oil. It's the detergents, seal conditioners, anti-foaming agents, and other additives that wear out. Those additives rarely last much more than 3,000 miles. If the oil is able to be whipped into bubbles, (foam), that is real easy for it to sneak past the piston rings and be burned, then go out the exhaust. The black soot is evidence of that. You can verify that's where the oil is ending up by adding a small bottle of dark purple dye to the oil, then check a day or two later with a black light. That dye will show up as a bright yellow stain. If you find it inside the tail pipe, it is coming past the piston rings or the valve guide seals.

If the oil usage was a problem since new, it is not likely to be caused by the valve guide seals. Instead, if you switched to synthetic oil too soon, the engine may have never become broken in. The piston rings won't wear to seat and seal properly, and that will lead to excessive oil consumption.
Mar 29, 2017 at 2:17 PM