Evaluating a Used Car - DipStick (Oil) Reading

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I'm looking at a 2002 Dodge Grand Caravan 3.3L with 57,000 miles. I pulled the dipstick and the oil looked dark and smelled a bit cooked. The vehicle had been taken in trade at a [Dodge] dealer. The salesman
showed me the shop work that had been performed on this vehicle to ready it for resale. Among other things such as brakes and stabilizer bushings, the engine oil and filter had been changed. The van had about 50 miles on it since the oil change.
Although I put a deposit on the 2002, I am concerned about the care that the engine was given by the previous owners.
Why would the oil be dark so quickly?
What inspections or tests can be performed to determine the overall health of the engine?
When I change the oil in my current van (1994 Dodge Grand Caravan 3.3L with 180,000 miles), the used oil is very dark, nearly black at 5,000 miles. The fresh oil is nearly clear and it takes a few hundred to a thousand miles before the oil is dark again.
I also have a 1997 Corolla. I changed the oil last week and have driven over 1,000 miles since the change. I check the oil level today and the oil is still clean and clear!
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They oil may be contaminated due to excessive blow-by caused by worn out piston rings among many other things -- this would be a very bad thing as it would mean engine rebuild. It may also be an issue with something not working on the emissions side of things, which might be cheaper/easier to fix. Definitely, if the oil was indeed changed, it should NOT look black after 50 miles.
To check the condition of the piston rings you can have compression test done on the engine, which effectively will tell you whether the rings are good or not to some extent.
Hope this helps,
Alex
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To separate the blow-by hypothesis from the other things, could it be as simple as removing the oil filler cap and seeing how much smoke comes out? A compression test might be better, but the smoke test is fast and free.
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Blake wrote:

    You can't separate the "blow-by hypothesis" because that theory is incorrect. If you change the oil often enough you can keep the inside of any engine clean even if it burns a quart of oil every 50 miles and it has compression of 50 lbs. and leaves a trail of blue smoke wherever it goes.     It may well be that because the oil wasn't changed often enough the rings are more worn than they otherwise would be. And/or it may well be that because the engine used a lot of oil the previous owner thought that the oil didn't need to be changed very often because they were always adding oil. So there may well be a correlation between the appearance of black oil and blow-by. But the cause of the oil being black is not blow-by. It is either they didn't really change the oil as the salesman said or the engine has a history of the oil not being changed as often as some people do. In my opinion its unlikely that they skipped the oil change if they were seriously trying to sell the car. As for the other theories that they didn't drain all the oil or didn't change the filter - it is much more likely that the previous owner was the one doing those things. The dealer probably changed the oil and filter properly.
-jim

-
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It's hard to say. Likely as not, they falsified the work report. I bought a car from a Dodge dealer just a few weeks ago, and they had records showing they did work that was obviously not done. Who knows.
3.3's are pretty tough.
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Joe wrote:

My first thought also. It would be rather hard to *truly* damage a 3.3 in only 57k miles. Yeah, extreme, extreme neglect would do it, but that should be fairly obvious in other ways. I bet they just didn't change the oil.
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obviously impaired state, wrote:

Doubtful on the oil, from your description. Since the oil change info is suspect, I'd figure that the rest of the service invoice is bogus as well.

I hope it was a refundable deposit.

Only reasons I can think of is that the oil filter wasn't changed, or the old oil was not completely drained out, or you were present with a fraudulent service invoice. My impression is the latter.

Time to do that was BEFORE you put down a deposit. You would have done that by taking the car to a reputable garage and asking them to check it out for you.
--
Ray Sirois
SysOp: The Lost Chord BBS
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That is a severe inconsistency. I'd not believe anything they say, even the mileage, and would pass on this one.
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snipped
I might think twice about paying them to do an oil change in the future too. - sounds like someone may have been paid for a job he didn't do.
--
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If the oil was not changed often enough or never changed, you will get a build up inside the motor. When you do replace it and start driving the old build up (dirt) blends in with the new oil. That makes it black and will take out the bearings down the road. I always change mine between two and three thousand miles.
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HKEK wrote:

If the oil gets dark after 50 miles of driving at 180K this is pretty much normal for any car that has had the oil changed at extended intervals of say 5000 to 7000 miles. Had the oil been changed more often it would take considerably longer for the oil to become dark. Basically what is causing the oil to become black is grime that has accumulated inside the engine.     The engine may still be in good shape. Check the tail pipe. If it is coated with black soot then the engine is probably beyond hope. But if the engine runs well and is still in good shape you can clean it out by changing the oil whenever it gets dirty. That may mean changing it at 50 miles for the first oil change, but the next one will be longer (maybe 500 miles). After following a regimen of changing the oil whenever it gets dark for a while you should be able to get it back to where it will stay clean for thousands of miles.
-jim
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I can have the vehicle inspected and the deposit is refundable if my mechanic finds any serious issues.
It has been suggested that some shops do not drain the oil during changes but pump it out instead through the dipstick tube. It was further suggested that this practice may leave enough used oil behind to contaminated the fresh oil being added.
When I drain oil for a change, I drain it hot and for an hour or two if not overnight.
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If they're not getting underneath the car to drain the oil, then they might also be not changing the filter...

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Correct.
That's how I do it. The shop I go to does remove the drain plug for about 15 min.
Over the years I've noticed very very dirty oil in some rental cars with over 15K miles on the clock. I'm sure they only change the oil just before selling the rental. How to shorten engine life! I'll not mention the worst rental car oil I've noticed, not wanting to be sued! <:)
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After doing a little test, I believe the oil had been changed before I put a deposit on this car.
I had the dealer change the oil and filter and I drove the van around for about 15 miles. I then collected some of the oil from the dipstick into a glass vial. I repeatedly insert the dipstick into the crankcase, withdrew it, and wiped into the glass vial.
The dealer saved some of the original oil in a glass jar.
I also got a sample of the fresh oil, which was Citgo 5W30.
Well, the original oil was very dark and smelled a bit like gasoline. The fresh oil was very clear, a bit yellow, and had little scent. The oil that had been in the crankcase for 15 miles looked about half as dark as the original oil and also smelled a bit like gasoline.
Does this mean anything of significance? I think the previous owner(s) ran the car beyond the recommended service intervals (oil & filter change) and I believe the fresh oil, with its detergents, is cleaning up deposits on engine surfaces.
I will have a compression check run on the front 3 cylinders (the back 3 are require removal of the intake plenum).
If I end up buying this one, I will probably change the oil at extremely short intervals (~100 miles or weekly) until the oil stays clear.
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On Wed, 23 May 2007 19:01:11 -0700, HKEK wrote:
<snip>

Correction - if you end up buying it, you'll be an even bigger fool than you appear to be now.
--
"Ubuntu" -- an African word, meaning "Slackware is too hard for me".


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HKEK wrote:

Hi..
The real question is how fast can you run? And how quickly can you start?
Take care.
Ken
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Just fill the crankcase with diesel fuel instead of oil and run it at temp for five minutes or so. Diesel is a good lubricant, so no harm to the engine, but it's also high detergent, so it'll clean. Then drain & fill with motor oil. Do that at your next two regularly scheduled oil changes and your engine ought to come clean unless it has other problems. No need to waste a bunch of motor oil and filters. I always put a quart of diesel fuel in my engine a day before I do an oil change to keep everything clean. On lawnmowers I'll actually fill it up with diesel and mow a lawn.
--
B.B. --I am not a goat! thegoat4 at airmail dot net

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Sounds like the oil is filling with gas. This will 'fast' destroy the engine if it already hasn't done so.
A compression test will not tell you about all the dead crank and cam bearings, only the rings and valves which aren't parts killed fast by gasoline diluted oil.
You really need an oil analysis on it or to just walk away now.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
HKEK wrote:

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The "Dark Oil Myth"...
http://www.nordicgroup.us/oil.htm#The%20Dark%20Oil%20Myth
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