Thee trend is a bit disturbing but how's the crankcase breather working and what oil are you using?

 

Don't know...what is a "crankcase breather"?

Oil is 5W30 full synthetic high-mileage....

 

@Big Buford

May I ask if the .76 qt is representative of the miles driven prior to 146955 and therefore:

149109 - 146955 = 2154 @ .93 qt call it 1 qt per 1k is ~2 qts.

151220 - 149109 = 2111 @ 1.07 qt call it 1 qt per 1k is ~2 qts.

So leakage is bad but not worsening. I realize the variables cannot be calculated. I only mention it because it might help identifying where to look.

No exhaust indicators. Presume one spark plug was pulled to verity.

It's oily underneath meaning you need to get the car up with bright 120v light sitting on ground and all 4 wheels on safe stands and get under it. Look for a spread direction. Just laying there generally gazing up at it will often reveal a flow pattern. You need to allow your brain to take driving forward into account.

Then while it's safely up, start at back wiping oil off with dry rags and look for places where oil is higher-up and tag area with tape after wiping and proceed with cleaning all the way forward.

The front structural members will often gather pools of oil that drip into then from above then travel to the member's low spot. So next check is any gaskets area above a front structural member.

If that doesn't reveal leak source(s) then leave a big tarp or a single uncut cardboard or some such under it while on the stable stands. At that leak rate it should reveal in ten minutes or so. But leave it on the stands overnight if able. The tarp etc should have drip marks. Measure for grid or crawl under and look above each drip.

In your case I think this is a better investigation than using fluorescent oil leak additive. That loss quantity often indicates multiple leak points. And being a stable leak rate over thousands of miles usually indicates wear rather than damage or a large failure.

Imo during your clean-up do what you can to clean at the valve covers. If inconclusive, change valve cover gaskets.

If intake gaskets had failed then performance would usually present telltale indicators. But do a visual anyway, best able.

I hope you'll tell us what you find.

.

 

May I ask if the .76 qt is representative of the miles driven prior to 146955 and therefore:

149109 - 146955 = 2154 @ .93 qt call it 1 qt per 1k is ~2 qts.

151220 - 149109 = 2111 @ 1.07 qt call it 1 qt per 1k is ~2 qts.

So leakage is bad but not worsening....

146955 ~0.76
149109 ~0.93
151220 ~1.07

The oil usage is normalized, so it's in units of quarts of oil used per 1000 miles. Just changed the oil at 151220. The previous oil change was at 149109. So the miles driven was the difference, which is 2111 miles. During that time it used 2.25 quarts of oil. So that would be 2.25 quarts/2111 miles, which is ~1.07 quarts/1000 miles. Unfortunately the trend is worsening....

 

@GrivChev, Thanks for the investigative strategies laid out nicely...will consider those. For now, the Impala is with my daughter away to college.....I get to see the vehicle sparingly....like when it needs gas....then only for a few minutes. Got my hands on the Impala long enough to change the oil yesterday and did the sad calculation wrt oil leakage. Will keep those investigation techniques in mind.....

 

Yep I get it. My math should be correct based on what you've posted. There's no start mileage to match end milage 146955 ~0.76 so from posted info cannot know how many miles were driven ending at 146955. So cannot trend that. And the other two are identical considering you can't really account for exact quantity added unless you used a measuring cup and even that and you can't rely on the dip stick unless all measurements are taken at same temperature. So it's reasonable to do the math the way I laid it out. It's so close the the same miles for about the same quantity.

Anyway it's moot. Fluorescent additive will be challenging and is likely to leak from multiple places (oil must be shedding on the road while hot or there would me a mess on the parking surface).

These things are interesting. I look forward to hearing back about the solution!

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