I've recently noticed a case of vanishing oil on my 97 Grand Prix GT. 3.8l NA rebuilt with 40k on the engine since then. I use full synthetic Mobile 1 oil and I've noticed over the course of say, 2 months give or take I'll go through about half a quart or a little more. I have heard that these engines tend to just do that but I don't really believe that. I don't see any leaks (on the ground anyways) or smell any burning oil. Ideas?
97 Grand Prix GT Case of mysterious oil disappearance.
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You'll want to check your top-end gaskets (valve covers, lower/upper intake, etc.) along with the usual culprits like front/rear main seals and oil pan gasket. Also, see if the PCV valve is drenched in oil, and just get a general idea of what the current condition of things are. This may be a drawn-out diagnosis to make sure you only end up having to fix whatever the exact issue may be.
The PCV was replaced not too long ago and the lower/upper gaskets don't have any oil around them. Unless the gaskets are leaking internally... The oil pan gasket looks a little nasty but there's never any oil on the ground. I'll check out the valve covers, main seals, and I might pop out the PCV valve sometime. Gotta wait for it warm up outside a little more though.
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If your engine is anything like mine (3800 Series 2, NA) then that sounds pretty normal to me. I run full synthetic too at the viscosity recommended by GM (10w30) and I easily go through a quart to a quart and a half between 3,000 mile oil change intervals. Like you, I have zero oil leaking on the ground and I recently replaced both valve cover gaskets when I did the upgraded LIM gasket and UIM gaskets about 2 years ago. The engine is clean as a whistle and there's nothing on the ground where it's parked. I do know that if I REALLY get on it, it'll smoke a little bit from the tailpipe. I normally drive my car pretty much like a grandma, so that could just be carbon build-up. That said, I think GM might have designed it intentionally to have oil blow-by a little on the high side. Given how long these engines last when treated properly, it's probably OK. While extra oil blow-by isn't exactly environmentally friendly, it's definitely engine friendly IF that's what the engineers had in mind by design. Don't forget too that these 3800 engines are just like their smaller 3400 V6 cousins - GM specifically engineered them to where the piston rings will actually contract quite a bit to allow more oil to blow-by in the upper cylinder chambers when the engine is started cold. The obvious drawback to this design is increase oil consumption. My advice would be this: if she's running good and healthy and not giving you any problems or leaking any oil - just keep an eye on your oil level, be nice to the ol' girl, and keep on truckin'.
I've heard it's a common thing. It runs fine and still pulls good so I'm not too worried about having to check the stick every now and then. If that's how it's supposed to be then so be it.
Could be, they're fairly new still though. None on the outside of the gaskets but if that is the issue then it would be internal.
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Have you looked and smelled the coolant in the overflow bottle?
Yeah, doesn't smell of exhaust/oil or look contaminated at all.
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Could be oil pan gasket, back valve cover, possibly ops. Hope it's not heads
The oil pan gasket seems a little nasty, I've yet to see if it's just buildup and grime or oil seeping out. It's on my list of replace once I figure out how to get to the one damn bolt that's blocked off. With the rebuild it's unlikely it's anything internal.
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You gotta take that bracket on the right side that affixes to the pan. I had some seepage on the very bottom of my pan. Come to find out I had a slight crack. Aluminum pan sucks and not cheap but replaced it, new sensor and no more. Are you having to add oil at all?
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