My mechanic overfilled the motor oil; will this be a concern?

http://boards.straightdope.com/sdmb/showthread.php?t=692869

A quart too much is a lot too much.

I’d bring it back to the mechanic and have him rectify it. I also don’t think I’d be using that mechanic any more. Did he admit to the mistake?

How are you judging by the dipstick? This is an important question, because if you’re checking a warm engine you won’t get the accuracy of a reading from a cold engine (with the vehicle on a flat, level surface and the engine obviously turned off).

Otherwise, yes, if the oil level is too high you risk damaging seals and leaking oil while the engine is hot, which will be messy at best, and smoky and potentially more damaging at worst.

½ quart may not be a problem but 1 quart might be too much. The oil level on most engines is right at the top of the oil pan. Remove the oil dipstick, mark where the oil is now, then hold the dipstick up to the dipstick tube and see where the oil level is in relation to the top of the pan. If the oil is above this level, have some drained out.
(FYI Why is high oil level dangerous to my engine? If the oil level is too high, the crankshaft will strike the oil as the crankshaft rotates. This extra vibration/resistance can cause the crankshaft to crack, or break.)

Depending on how much, it could be a serious (as in “engine killing”) problem. And I’d say a quart is probably enough to get into dangerous territory.

It starts with frothy oil that won’t lubricate bearing and maybe a blown rear main seal that drips. To quote one source, “You’ll know bearing damage when you get it. The engine smells like a garage mechanic cooking over an open flame and the noise coming from the engine is the sort of thing you’d normally hear in vaudeville plays when a piano is pushed down a flight of stairs.”

Then it progresses to blown front mains, a.k.a. “pissing oil all over the place”. This assumes you don’t bend/break a connecting rod or something first. Also, some of that oil will probably wind up in the bore and thus burnt and shot out the tailpipe; that isn’t good for your catalytic converter.

Read this if you want testimonial though. The TL:DR version is that a quick-lube place overfilled the guy’s truck by 3 quarts and it died 5 days/175 miles later. Common story though.

In no way will any good come of this.

Update.

@jca I took the car back to the mechanic, and he admitted that it was overfilled. He removed the extra oil, which he said amounted to ½ quart, but did not apologize for the mistake.

@CWOTUS My understanding is that the oil level should be measured after the engine is sufficiently warmed up. I then park the vehicle on level ground, wait 5 minutes, and then measure the oil level with the dipstick. Is this not correct?

My estimate of 1 quart excess oil is based on this dipstick observation. There are two very small holes on this particular dipstick. If the oil level is at the top hole, then my understanding is that the oil level is at “full”. If the oil level is at the bottom hole, then it’s down a quart. Well, the oil level was above the top hole by an amount equivalent to the distance between the two holes. In other words, if the distance between the holes is ½ inch, the oil level was ½ inch above the top hole. This estimate would be correct only if the sides of the tank are parallel all around. I don’t know is that’s the case, so my estimate could be wrong (I hope so), and the mechanic’s estimate of ½ quart could be correct. Hopefully the mistake was caught in time, and @jerv‘s fearsome scenario won’t happen!

@2davidc8: Will you be returning to that mechanic?

On most cars I’ve had, the difference between the Min and Max lines is about a quart, and the marks are about an inch apart, so that’s not a bad estimate. But yes, the shape is not consistent, so best to double-check just to make sure.

@2davidc8 you’re allowed a certain amount of leeway in checking your oil levels. That’s what the hash marks mean at the top of the dipstick measuring point: “your level should be in this area”. Because obviously, if you’re driving across country and want to stop for fuel and check your oil, you don’t want to sit there for four hours (okay, 20 minutes in New England at this time of year) for the engine to cool to get a “cold” reading.

The fact is that oil, like many materials and fluids, expands a bit as it warms, so your level will change based simply on the temperature of the fluid. In addition, as you operate the vehicle the oil is moved through its cycle to lubricate the various pieces and parts that it has to lubricate, so a recently-run engine is going to have a certain amount of oil – because of its viscosity – still draining into the pan. (In point of fact, the warmer oil is also somewhat less viscous than cold oil, so you’ll want to drain “warm” oil from an engine in order to change it, because that way you’ll be draining the highest quantity of used and contaminated oil.)

I’m not going to tell you to do anything against the advice of the vehicle manufacturer, who will undoubtedly have perfect technical instruction on how to measure your oil level. But as you gain experience you’ll also know that there are many acceptable methods: before operating the vehicle and while it is “cold” will give you one reading, and by using the method you described will give you a slightly different reading. (Try both ways over a period of time to get an idea of the difference that “the same level” may indicate. This is also a good way to become familiar with your car under the hood when “cold” and when “hot” and how to recognize what is normal in both cases. Be careful while under the hood with a hot engine; some parts retain more heat longer than you might expect – and hotter, too! – and can cause significant injury. You should also be aware – and surely your owner’s manual will mention – that certain electrical and mechanical systems in your car may operate unexpectedly, such as electric fans that may continue to operate, or turn on and operate by themselves, in a recently switched-off vehicle.) Definitely read your owner’s manual: RTFM.

Your way of measuring is just as valid as mine, but if you only take one cold reading and one hot reading you may think there’s a problem when all you’re really seeing is the normal variation between “hot” and “cold” of the same – perfectly normal and acceptable – level of lubrication ability.

PS: While you’re looking at your dipstick also look at the color of the oil. Although oil is popularly considered to be black, if you look at new lubricating oil poured into your oil reservoir you’ll see that more often than not it’s a mellow, brownish-to-golden honey color. If your dipstick is showing “black” oil, then it’s probably time for an oil change.

@CWOTUS ” If your dipstick is showing “black” oil, then it’s probably time for an oil change.”
Even that is a little variable. If that were strictly true, most of the cars I’ve had would be ready for an oil change about every 8 minutes or 4 feet. After 25 years and 150–250k miles, most engines will discolor oil and turn it dark brown almost instantly; dark enough to look almost black. While you are correct that black oil should be changed, I feel I must point out that there is a difference between “black”, black and BLACK. If you’re going to go by color, check it in light no dimmer than a clear, sunny afternoon.

@jca That shop has done excellent work for me in the past. Lately, though, I feel that the quality of the work has slipped, and I’m starting to lose confidence. Prior to the motor oil incident, I noticed that the gas mileage that I was getting was significantly lower after they replaced the distributor. I had them check the timing, and indeed it was a bit off.

@CWOTUS The manual for every car I’ve owned has always specified a “warm” motor oil reading, as far as I remember. So, I’ve always followed the protocol that I described. Typically, the oil level is just a tad higher when the engine is warm. I suppose if I’m consistent when checking the oil, I’ll be OK.

When it comes to changing your car’s oil, being black isn’t a reason. What breaks down is the oil’s corrosion inhibitors. The black stuff is carbon, which is an excellent lubricant.

Hot or cold I always get the same reading on the dip stick . Now the trans is to be checked cold for the best reading.

@fredTOG Every car I’ve had except one specified measuring the transmission warm, or “normal operating temperature”. That one exception had two sets of marks with a considerable distance between the “hot” and “cold” sets.

@jerv yes that’s right I meant to say hot. oopsy .