Buying a used car: How to detect excessive oil consumption?

Joined
Jun 14, 2011
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Denmark, Europe
Hi,

Lets assume the following:

You reacted to a classified add for a used car and now you are on your way to see the car at the private sellers place. You arrive and the car runs great. No smoke. No weird noises. Oil dip stick OK. No mayo in the coolant. The whole nine yards. You buy the car and start driving it. After a while you realize that it has an excessive engine oil consumption in the range of 1 liter pr 1000 km, I guess that is 1 pint for every 600 miles.

How could you have detected that excessive oil consumption before buying it? What test could you have done?

Lucas

PS: Of course the seller will not admit that oil consumption and of course he has topped up the oil before showing you the car.
 
Joined
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All I can think of is to have someone watch from behind the car while you drive it, accelerating, decelerating, etc. Many times they might be able to see the smoke from behind the car, while you could not see it watching the rear-view mirror while driving.
 
Joined
Oct 11, 2020
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Wear a white glove and take a swipe inside the tailpipe. If you see lots of soot, then question the engine health. When my TL was burning oil before the warranty piston work, my white bumper above the tailpipes had a dark coating that was difficult to take off.

 
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That white glove test is kind of invalid on any direct injection car. Both my VWs are DI, burn no oil between oil changes and yet have sooty tailpipe interiors. Nature of the beast.
Agree. DI cars naturally emit high amount of soot. I was thinking of older non-DI engine cars.
 
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Most oil burners won’t emit blue smoke, not until ridiculous levels.

IMO its a gamble. Just make sure you don’t overpay, that way you won’t feel bad if you have to add a quart every 1k. Unless if it causes issues with inspection or otherwise at the garage, then it just goes with the territory. There’s a reason why cars deprecate.
 
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Jun 15, 2003
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Drive down a hill so you've got fuel cut-off then nail the gas. If you have an automatic, use manual 2nd gear. Stick shifts can use 5th. The extra oil will be drawn past the rings or valve seals and either coat the spark plug or build up on the piston crowns.

When you hit the gas, you'll feel a little hickup from the fuel shut-off turning back on. But if you feel a bigger hickup it's the car pulling timing from the low octane of the burning oil or from clearing the plugs.

The problem with this test is you have to know what your car feels like, so it's only good if you're driving a comparable car to one you have experience with.

You should also have a feeling for how much road grime should be on an oil filter vs how dirty the oil is, assuming you can see the filter, and assuming the seller didn't slap a new filter on "to set the next owner up for success."

Similarly, there are subtle differences in the appearance of used oil: Sooty 5k oil mixed with virgin top off oil looks different than a full load that's gone 2500 miles. But again different cars soot their oil up differently.

The easiest way to see if a car consumes fluids is to look in the trunk, sometimes they leave a bottle there! Also look to see if fingerprints have gotten to the road grime on the dipsticks and fill points of everything under the hood.
 

CKN

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Pull the spark plugs and check for burnt oil deposits on them.
Probably the best suggestion (for really detecting an issue)-but also the most unpractical. Any private part owner isn't going to let you do this.
 
Joined
Apr 2, 2022
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Another way to think about it is compared to how much fuel is going to cost you for driving 1,200 miles a quart of oil is not a lot of additional cost.
 
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Joined
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You arrive and the car runs great. No smoke. No weird noises. Oil dip stick OK. No mayo in the coolant. The whole nine yards.
Then why are you concerned if it uses some oil? Sound like a healthy engine. The amount of oil consumption you describe wouldn't even be considered a warranty case on a brand new car.
 
Joined
Jan 22, 2011
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If it is being sold by a private owner, I am always very cautious if a fresh oil change was just done.
 
Joined
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I just check in and around the tailpipe for oily, sooty deposits.
This has worked for me, for 30+ years.
My current GDI engine had a little soot in the pipe, but it's dry.
 

JTK

Joined
Aug 14, 2003
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Buffalo, NY
Much of the above can be covered up with an attention to detail, good cleaning, fresh oil change, new spark plugs, etc.

Like said, there is always a risk when buying something used.

To me, best you can do is check over the interior and exterior the best you can. If it's all clean with mostly original parts/pieces, that says something. If the interior is beat, the car was likely not maintained either.

Is it the original owner or multiple owners? How does the carfax look. Is there maintenance records?
 
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That white glove test is kind of invalid on any direct injection car. Both my VWs are DI, burn no oil between oil changes and yet have sooty tailpipe interiors. Nature of the beast.

I get what you're saying however sometimes it's even vice versa: My GTI is a DI turbo (non-GPF) and the tailpipe remains surprisingly clean while both my Mini Cooper and my old Porsche (both port injection) are kind of sooty. None of them burns considerable amounts of oil btw..
DI has come a long way compared to its earlier generations. Vastly inceased fuel pressures (1500 psi > 2900 psi > 5000 psi), improved injectors etc..

Yes, it's hard detecting oil consumption when buying a used car, but I'd still check the tailpipe(s) with a towel, while of course taking into account what's common for that particular engine. Also check oil level, service history, overall condition.
.
 
Joined
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Maybe look at the oil filter. If it's old and rusty the owner probably never changed the oil and instead just topped it off.
 
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