Suppose one is looking at a used car that has little or no documented history of oil changes. Would a compression test or (any other test) be indicative of proper maintenance? Frankly, I’m surprised there isn’t a sensor that trips each time the oil level goes to zero and records the event. Or is there?
In my experience and what I see on Youtube, the best quick test would be to pull the valve covers off and look for sludge.
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I’m not aware of any verifiable way other than dealer records from the owner’s visits.
I try to use other indicators when buying used. If I’m buying from an individual I try to get a good look at their home. If possible, I claim a need to use the restroom so I can get inside too. If everything else is in good repair, they probably took good care of the car (or boat, etc.) as well. If there is evidence of shoddy care and unrepaired elements of the house/fence/yard, then I pass on the vehicle. It will be last on the list, and probably hasn’t been maintained as it should.
It’s not a perfect system but I think those are good indicators of an owner’s maintenance habits.
A compression test, or the (even better) cylinder leak down test, is typically done to see if the head gasket is blown or a valve is bad. I don’t think it’s a good test for determining premature wear of the rings due to infrequent oil changes. Though I suppose if they’re very worn it might give a low reading.
Unfortunately I don’t think there’s a good, simple test for determining how often the engine oil has been changed in a used vehicle. But I’m certainly not an expert in the area, so will be watching this thread.
Don’t mean to hijack, but do people actually let you, a total stranger, into their house? That’s not something I would do.
A neat-looking exterior and a reasonably well-manicured yard would be good enough indicators for me to determine if the person takes pride in their possessions.
/endhijack
Brand new oil can also be a red flag. Likely an attempt to hide dirty oil, metal particles or water in the old oil.
I recently got a new vehicle, and I was shocked when the dealer drug out this huge list of every maintenance activity I’d ever had done at a commercial facility for my old truck. Like every oil change, tire rotation, new tires, etc. over 18 years. Of course, it didn’t include the home oil changes and similar stuff (spark plugs, etc.).
I think in fact, it was Carfax. So you could try that to get an idea of what commercial maintenance was done.
I always check the oil as a matter of course. I look at level, cleanliness, and the presence of foam. (More on the latter below.) Another thing to look at is the oil filter, if it’s easy to access.
- Does it look like it’s been on there for many years?
- Note the brand, then ask them where they take it to for the oil change. Does that place use that brand of oil filter?
- Some oil filters will also have a date code.
- If the oil is very clean, and the oil filter looks like it’s been on there for a long time, then that’s a definite red flag.
If someone says they change the oil themselves, then the oil filter should be a brand that is typically sold by retailers. I’ll also ask them the capacity (in quarts or liters) and viscosity they use. If they can’t answer that, it’s a red flag. (If they can answer that, I’ll ask them what the torque spec is on the drain bolt, and they will get major bonus points if they’re able to answer it.) I will then ask them how they’re able to track the number of miles between oil changes. Note pad? Spreadsheet? I’d like to see it.
That’s a different issue (blown head gasket), but one that should also be looked at. Remove the oil filler cap. Look at the underside of the cap, and look into the opening. Is there thick foam? Check for foam on the oil dipstick, too. Also look at the color and density of the smoke/mist from the exhaust when the engine has been running for at least 15 minutes.
If oil goes to zero, an event is recorded. The recorded event is that the engine seizes up and has to be replaced. Some cars will have dash sensors that come on when oil is low. That’s usually when it’s just a quart down. That may be stored in the car’s computer, but there likely isn’t much history. Once the oil has been topped off, I think the low oil event is cleared.
Is there a particular reason you’re worried about oil changes on this car? I would expect that many cars would have spotty oil change histories with services like CarFax. For instance, I take my cars to an independent mechanic who’s not affiliated with those recording services. I’ve done regular oil changes, but they won’t show up on a CarFax for my cars. None of the maintenance I’ve done will show up. The only place the repairs are recorded are in the large debits in my checking account 
Which is fine. I do my own maintenance, which is also fine.
But how do you know when it’s time to get your oil changed again? Is there a small mileage sticker on the windshield? Do you keep a record of oil change mileage in a notebook or spreadsheet?
These are questions I will ask a seller who does not have oil-change records from a shop that subscribes to one of those databases.
I own a lot of old cars. I keep a detailed spreadsheet of every maintenance item I do on them. If I were to sell one, I would provide them the spreadsheet.
(Of course, someone could produce a fake document/fake records. But I doubt very many people would go to the trouble of doing that.)
This might be the case on newer cars, as some have oil level transducers. But older cars simply have an oil pressure sensor or oil pressure switch. On these cars, if the “oil light” comes on, it’s a serious event. As in, turn off the engine, now.
Yeah. Big difference if we’re talking a used 1990s car, a used 2010s car, or a used 2020s car.
Do rings wear anymore? I thought they were looser than they used to be (I forget the term for these types of rings, low tension?)
I always do my own oil changes and track it on an Excel sheet with date and mileage (I aim for oil changes every 5K miles). I include air and cabin filter models when I change them along with the oil and filter specifics. 4.8qts of Pennzoil Platinum 0W-16; WIX 10332 filter. I suppose I could be accused of forging that info but honestly, who would bother forging that info?
29 ft-lb. And here’s my torque wrench I use.
I told you, Excel spreadsheet. I gave you a copy. Are you going to buy my car or not?
The sludge from infrequent changes plays hell with the VVT.
There really isn’t a noninvasive way. I guess I use the overall appearance as a guide for the previous owners’ diligence. That’s hardly any better than someone’s verbal assurances but about all one can do without external documents.
Heh, don’t see that every day.
I assumed that if the oil goes to zero while the engine is running, its catastrophic and would be recorded. Obviously, the engine is not running during an oil change. It would seem to me that it would be trivial to have some sort of level sensor that works along with all the other stuff that don’t require the engine to be running to receive power. Carfax is a big help but some places like Jiffy Lube don’t share their data with them.
The reason I’m asking about a “test” (or whatever) is that I’m seeing vehicles, mostly at dealers, that look, on the surface, like they were taken care of but have almost no maintenance history on Carfax. Clean or recently changed oil and a new filter at dealer that is selling a used car is almost a given from what I’ve seen.
Maybe I’m overthinking the whole thing but I have the time to do so. Meanwhile, I can keep waiting for the “unicorn” of a car to come along, private or dealer.
One last thing - the price range I’m looking means that timing belt replacement, for those that have one, is a consideration. I’ve looked any many Carfax reports and have never seen timing belts mentioned - just “Recommended Maintenance”. Fortunately, the service places mentioned on Carfax don’t seem to be reluctant at all to say whether or not they did the timing belt. So far, none have, even though "Recommended Maintenance’ appears at the appropriate mileage.
Thanks for the input.
my workaround: look for cars with timing chains, that need not be changed … timing belts is a normally quite expensive mainainance procedure (high triple to low quatruple $$$).
That way I ended up with a Honda Fit … and a Volvo V60 station (with the belt change recently done (but otherwise quite a dog of a car)).
Unless it has chain guides that disintegrate, cause the chain to jump timing, and the engine destroy itself. In many ways I’d rather have a belt that’s been replaced on schedule, than a “lifetime” chain, that nobody has ever looked at.
I think the best thing to do is buy a one owner car from some old guy who’ll give you a folder full of receipts going back to new.
If the oil looks preternaturally clean, test drive the car, then look at the oil again. If it was changed for the first time in years just to look good, it’ll have that honey look when you first look at it, but then after the test drive, it’ll be noticeably dirtier. So remember, too, to check the oil before and after the test drive.
Also, look at the filler cap. If turning it recently to fill the oil pan has cut a circle in some built up grime on the top, then it not only probably isn’t changed often, but it’s leaking somewhere under the hood where it can contribute to that grime.
A lot of people don’t use a torque wrench on the drain bolt, but if the answer is that they finger tighten as much as they can, then use a wrench until they get resistance, then give it one more quarter-turn, that’s a reasonable answer that is something someone who really changes oil could do, AND it is something that is fine for threads on the bolt and pan.
On the other hand, someone who says they use an electric or impact wrench, is either lying, or doing something that has likely already damaged the threads. Ditto anyone who says they get the bolt as tight as possible with a socket wrench.
Another question to ask a self-changer is where he disposes of the oil and filter. He should say he takes it to a parts store that has disposal, or he takes it to some recycling/hazardous waste center. Or he might say he pours the oil out in the woods and the filter in the regular trash-- heh, heh.
If he looks puzzled by the question, or says he throws it away with no indication that he knows he shouldn’t, he’s probably lying altogether.
Yea, as someone who has done hundreds of oil changes over the last forty years, it’s pretty easy for me to determine if someone is lying or not if they claim to change their own oil. Here are a few questions I’ll ask, most of which have already been mentioned:
Do you get under the vehicle to do it? If so, what tools do you use to do that? (If they’re getting under the vehicle, I am looking for words like jack, ramps, etc. If I’m feeling bold I might even ask them to show me these things.) If they claim they pump out the oil from the dipstick tube, I will ask about the pump.
How many quarts do you add? What viscosity?
What brand oil filter do you usually use?
What do you do with the old oil?
If they drain the oil from engine’s oil pan (as opposed to using a pump), I’ll ask how they tighten the drain bolt.
How many miles per oil change? How do you keep track of these miles? Notepad or spreadsheet? I would like to see it.
If they claim they change their own oil, and seem to be stretching for answers on these, then that’s a red flag.
And as repeatedly mentioned in this thread, always check the oil. The level should be somewhere between “full” (max fill line) and “one quart low.” If it’s one quart low, and they claim to have just changed the oil, then that’s an obvious red flag. If the oil is significantly above the max fill line, then that is also a red flag: why would it be so high? In addition, adding too much oil to an engine will damage it, so a dipstick that shows an excessive amount of oil would be a deal-breaker for me.