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

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Sorry to say, on higher mileage vehicles (in particular) it is a crapshoot. The soot in the tailpipe test is invalid when it comes to vehicles that have 150k miles or more on them (and in some cases, on some vehicles, far fewer miles), they ALL have some soot in the tailpipe. Also, many used vehicles on the market have been started and moved many times in a short period of time, never warmed-up, and running rich at every cold start. These vehicles will often display considerable soot buildup in the tailpipe.
IMO, the best advice that has been given is to get some help to drive the vehicle for you while you follow and observe. You can tell a lot about a vehicle by just observing it when it is going down the road.
 
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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.
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.
So if you change the oil before selling, people think you're a scammer, but if you don't, people think it's never been maintained. You can't win.
 
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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.
Supton is the man, buying is a gamble, just don't overpay and plan on money to fix up your new girl, she will love you forever
 
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Bring a set of ramps with you when you go look at it and ask if the owner minds if you take a look underneath the car. At least you could see if any oil leaks have been wiped away. The owner's answer might even tip you off that they're hiding something.
 
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This is a great question, and unfortunately tough to answer.

I have personally owned an oil burner, and there were a few things it did/showed. One, smoke on hard acceleration. Two, if you pulled a spark plug they were either oil soaked or showed signs of oil burning. Three, tailpipes looked like a coal furnace.

Other than that? Check the oil usage history of that style engine/car through a google search. If historically they’re oil burners, guess what? The car you’re buying either is an oil burner, or soon will become one. I know some will say...not all (of whatever) oil burners will become oil burners. And they may be true, but chances are it will and there’s not much you can do about it.
 

LucasDK

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Thanks for all your answers.

I would never accept an oil consumption of 1 liter/1000 km even though manufacturers claim its within spec.
 
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Only thing you can do is check oil level, look under for leaks, smell for oil smoke and lastly hookup a scanner to check for codes or last time codes were cleared.
 
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I’ve done the ramp thing buying a used car. The owner had no problem driving it up on ramps I brought. I don’t thing many would let you wrench on it, but up here it’s normal for the seller to deliver it to a garage on your own dime to have a mechanic take a look at it. It all depends on how cooperative the seller is. It kills me that internet car purchasers will buy a car virtually sight unseen.
 
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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.
What kind of monster does an oil change right before selling? It's supposed to be over the OCI by at least 2k with oil black ... 😂
 
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While in neutral, plaster the go pedal to red line, the drop it in drive while plastering the brake pedal, then immediately switch off the ignition...then have someone look at the tail pipe while you do this....if there is purple smoke or green or lavender colored smoke, then its a burner...
 
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While in neutral, plaster the go pedal to red line, the drop it in drive while plastering the brake pedal, then immediately switch off the ignition...then have someone look at the tail pipe while you do this....if there is purple smoke or green or lavender colored smoke, then its a burner...
First post in 3 years and it's some nonsense like this? If you try that with some people, you'll be leaving by ambulance.
 
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Thanks for all your answers.

I would never accept an oil consumption of 1 liter/1000 km even though manufacturers claim its within spec.
My Volvo used oil from brand new, not as much as that but still noticeable.

I kept it for 18 1/2 years and 285,000 Km. It never increased.

My conclusion - Some engines use oil, and some don't.
 
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laser heat gun, as it idles to warm up, shoot around the cylinders and look for even heat. shoot the radiator and look for cold spots (plugged flow).

plug an obdc II and get fusion app for ios or torque for android (ios/fusion needs more expensive modern bt dongles, but fusion might give more sensors)

Set it up to record to a csv file everything, then you can open it later on your pc and look at how everything ran, how the engine coolant temp ran up. the o2 feeds, the fuel trim and air fuel ratio it should all make sense compared to the engine load and rpm numbers.

look for bubbles in the radiator reservoir, gooy or dirty engine coolant. Any any signs maintenance was skipped on other simple things, like even no dam windshield fluid. people won't put a dime into a car with bad oil burning, look for signs of 'screw it' i'm not fixing/doing that on less expensive mainenance or repairs that one would do i they felt the car had life left in it. And any one with a single quart bottle laying around anywhere, most folks have a mechanic change the oil, or a diy would use a 5 qt jug.

Lasty never buy a red KIA.
 
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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.
I guess I would pull the plugs on my Focus if someone really wanted to see them? It's pretty easy to do. On the subaru, no, its not happening.
 
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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.
Agree on both. I don't think there is practical way to detect this during the purchase period.
 
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New Orleans La
Put the car in drive and apply the brake, or the emergency brake, even put the AC on. Let the car idle at the lowest possible RPM for about 15 minutes or more. The engine vacuum will be at it's highest. If there are worn valve seals it will probably pull oil in and smoke. Possible if the rings don't have a good seal hopefully it's pulling in oil too. But still there is no guarantee.
 
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