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#1
Old 06-04-2013, 12:14 PM
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Auto Mechanics: how much is too much oil?

All references I've seen say not too put too much oil in the engine. How much excess is too much?

I just got a used car with a new oil change, and the (dealer's) service people put what looks to be about 1/4 - 1/3 quart over the max line, and am wondering if I need to drain some or can let it go.
#2
Old 06-04-2013, 12:44 PM
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The "high" and "low" marks on the dipstick provide a substantial safety margin, so being a few ounces over the top mark isn't a big deal. If you were able to drive it home from the dealer, then you're probably fine.
#3
Old 06-04-2013, 12:46 PM
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You don't have to drain it, but watch it carefully, which means check it repeatedly for a while.
I'd be very leary if you bought the car from a non-brand used car lot. They may have over-filled it because they know the engine burns or leaks oil
Just how are you determining that's it an extra 1/4 - 1/3 quart?!?
#4
Old 06-04-2013, 01:02 PM
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Too much would be when the crankshaft and piston rod ends are hitting the oil in the crankcase. This would cause the oil to foam and be full of little air bubbles. Air bubbles aren't a good lubricant.

For this to happen would be at least one quart too much and probably much more than that. An exception would be a car capable of high speed turns where the oil would slosh up the sides of the oil pan. Such vehicles have baffles or even dry sump oil systems to prevent this problem.

Too much oil is far superior to too little. I wouldn't sweat it. If you are worried, check the engine immediately after driving a few miles. See if there are a lot of bubbles on the dipstick. A few aren't anything to worry about, but if it looks like the foam on a poured beer, that's not good.

BTW: Way back in the day automotive engines were lubricated by having the crankshaft and piston rods splash the oil in the crankcase. There would be little scoops to push the oil into the bearings and even splash the cylinders. You can still find such systems on things like small lawnmower engines.
#5
Old 06-04-2013, 01:06 PM
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Quote:
Originally Posted by Machine Elf View Post
The "high" and "low" marks on the dipstick provide a substantial safety margin, so being a few ounces over the top mark isn't a big deal. If you were able to drive it home from the dealer, then you're probably fine.
Thanks - that's reassuring.

And leads to another question, in the other direction. I own a couple of cars which call for 3.9 quarts of oil. Frankly it would be easier and simpler to just pour in an even 4 quarts. Question is whether it's worth the effort to avoid overfilling by 0.1 quart.
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Originally Posted by HipGnosis View Post
I'd be very leary if you bought the car from a non-brand used car lot. They may have over-filled it because they know the engine burns or leaks oil
It's a possiblity I've thought of, but I doubt it. (They just got it in a trade last week - per CarFax - and I don't think they would be running that level of tests on it.)
Quote:
Just how are you determining that's it an extra 1/4 - 1/3 quart?!?
Based on how much above the full line it is. The space between the min and max lines seems to be a bit over 1 quart, and I'm assuming the same ratio above the line.
#6
Old 06-04-2013, 01:22 PM
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Originally Posted by Fotheringay-Phipps View Post
Thanks - that's reassuring.

And leads to another question, in the other direction. I own a couple of cars which call for 3.9 quarts of oil. Frankly it would be easier and simpler to just pour in an even 4 quarts. Question is whether it's worth the effort to avoid overfilling by 0.1 quart. It's a possiblity I've thought of, but I doubt it. (They just got it in a trade last week - per CarFax - and I don't think they would be running that level of tests on it.)

Based on how much above the full line it is. The space between the min and max lines seems to be a bit over 1 quart, and I'm assuming the same ratio above the line.
Don't sweat the 0.1 of a quart. Pour it in.

You're probably right about the dip stick unless the oil pan is V-shaped or something strange like that.
#7
Old 03-29-2014, 10:08 PM
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Reviving this thread, my car requires about 5.5 quarts when an oil change is done. I think the engine was overfilled by 0.5-1 qt at my last change. When I pull the dipstick when the engine is cold the oil is about 1/2"-1" above the full line. Is that going to cause any kind of damage? Everything I am reading says unless you get so much oil it causes a frothing then you should be fine.

Will the extra oil cause extra pressure that could damage gaskets or cause leaks?

Will the car just burn off excess oil?

Last edited by Wesley Clark; 03-29-2014 at 10:09 PM.
#8
Old 03-29-2014, 10:40 PM
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Quote:
Originally Posted by Wesley Clark View Post

Will the extra oil cause extra pressure that could damage gaskets or cause leaks?
This would be my primary concern as well. Hopefully one of our resident mechanical wizards can clarify.
#9
Old 03-29-2014, 11:05 PM
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Quote:
Originally Posted by Wesley Clark View Post
Reviving this thread, my car requires about 5.5 quarts when an oil change is done. I think the engine was overfilled by 0.5-1 qt at my last change. When I pull the dipstick when the engine is cold the oil is about 1/2"-1" above the full line. Is that going to cause any kind of damage? Everything I am reading says unless you get so much oil it causes a frothing then you should be fine.

Will the extra oil cause extra pressure that could damage gaskets or cause leaks?

Will the car just burn off excess oil?
The oil just sits there in the pan until it gets sucked up by the oil pump and circulated around. Having more oil in the pan doesn't really affect the pump pressure. Or at least not until you get to the point that the crankshaft is whipping air bubbles into the oil, at which point you'll get lower (possibly catastrophically lower) pressure. It also won't just burn off, or at least not any faster than usual (if it's like one of my cars).

On a car with a 5.5 quart crankcase, a half a quart over is probably okay but I'd start to be worried about a full quart. You might consider draining a bit out or taking it in and having them do it.
#10
Old 03-30-2014, 10:42 AM
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ITCSAMTTM, why can't "they" make an oil level meter? Granted, it would probably only be accurate when the engine is cold, but still, it would be more convenient than an oily old dipstick.
#11
Old 03-30-2014, 12:02 PM
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Quote:
Originally Posted by Son of a Rich View Post
ITCSAMTTM, why can't "they" make an oil level meter? Granted, it would probably only be accurate when the engine is cold, but still, it would be more convenient than an oily old dipstick.
Some cars do have oil level gauges. They add cost, complexity, and leak points while providing questionable benefit.
#12
Old 03-30-2014, 12:18 PM
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Quote:
Originally Posted by GreasyJack View Post
Having more oil in the pan doesn't really affect the pump pressure.
True, but it does affect air pressure inside the crankcase. I remember someone telling me that this could affect something else that relates to crankcase pressure, but it's all hazy now. EGR perhaps? I don't understand how airflow in the crankcase works, but IIRC, it's not as trivial as one might think -- that is, it's not just a dead air space.

I was told this when I asked someone I trusted the same question: overfilling oil. The answer was that overfilling a little is no big deal, but way overfilling can cause problems (most notably the frothing).

That said, I know I've occasionally overfilled a lawnmower, and never had any specific reason to regret it. The engine is always the last thing to fail. (I now have a cordless electric, we'll see how that goes.)
#13
Old 03-30-2014, 05:56 PM
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Quote:
Originally Posted by Learjeff View Post
True, but it does affect air pressure inside the crankcase. I remember someone telling me that this could affect something else that relates to crankcase pressure, but it's all hazy now. EGR perhaps? I don't understand how airflow in the crankcase works, but IIRC, it's not as trivial as one might think -- that is, it's not just a dead air space.
The PCV system vents overpressured crankcase gasses into the intake stream and lets fresh air circulate in. If you REALLY overfilled the crankcase, the system could start sucking oil out and running it into the cylinders, but considering that the PCV valve is usually mounted high on the valve cover, you'd almost have to fill up the engine until oil was overflowing out of the filler hole.
#14
Old 03-30-2014, 10:54 PM
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I've driven about 200 miles since I had the oil done, if I haven't had problems yet am I in the clear?

Also, would the engine overheat if there was too much oil? I'm not noticing that.
#15
Old 04-01-2014, 08:02 AM
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Quote:
Originally Posted by Learjeff View Post
True, but it does affect air pressure inside the crankcase. I remember someone telling me that this could affect something else that relates to crankcase pressure, but it's all hazy now. EGR perhaps? I don't understand how airflow in the crankcase works, but IIRC, it's not as trivial as one might think -- that is, it's not just a dead air space.
The issue is that the pistons going up and down can alter the volume of the crankcase airspace. The degree to which this is true depends on the engine. If you've got a 4/6/8 cylinder engine, then generally for every piston that's traveling upward, there's another one coming down. A piston's motion isn't perfectly sinusoidal, owing to the gyrations of the connecting rod, but for the most part, a piston moving up and another moving down pretty much cancel each other out as far as changing crankcase volume is concerned.

Where it can be more of an issue is in BMW boxer engines and single-cylinder small engines. In BMW's boxer-engined motorcycles, both pistons hit TDC at the same time, and also hit BDC at the same time. So crankcase volume fluctuates over a range of 1.2 liters every time the crankshaft completes a revolution. Four-cylinder and six-cylinder boxer engines don't have have this problem because the two/three pairs of pistons all reach TDC at different times.

Single-cylinder engines have the same problem, inasmuch as there's no second piston to cancel out the crankcase volume changes caused by the one piston.

Single-cylinder engines typically have a reed valve that prevents backflow into the crankcase as the piston moves toward TDC, thus assuring that the crankcase never sees positive pressure, which could compromise seals and cause pressure-driven oil leaks, as well as pushing oil up past the piston rings during the intake stroke.
#16
Old 04-01-2014, 08:08 AM
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One might ask the same question about the automatic transmission. Does overfilling create damage?
#17
Old 04-01-2014, 09:40 AM
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Originally Posted by crucible View Post
One might ask the same question about the automatic transmission. Does overfilling create damage?
Good question. While an automatic transmission usually holds much more fluid than an engine, it had a relatively small oil pan. Unlike automotive engines where the vast majority of the oil drips down into the crankcase and oil pan very quickly, a lot of the oil in an automatic transmission is trapped in places like the torque converter, transmission cooler, lines, clutch packs and actuators. If you pull the oil pan (or a few that have drain plugs), you seldom get half the oil out.

As the automatic transmission's oil pan is very small and close to the valve body, it wouldn't take much more that a quart to possibly interfere with the transmission's operation. Also keep in mind that the transmission doesn't burn oil like an engine, so an overfilled transmission could well stay that way for many thousands of miles.

Even worse though is running an automatic transmission low on ATF or using the wrong kind of ATF. There's many more variations in transmission fluid than engine oil such as Dextron, Mercon, Type F, SP-III and many more. However there are some synthetic formulations that match multiple standards.

For most automatic transmissions the method of checking the fluid level is different than engine oil. While you want both to be on a flat surface while checking the levels, you want the automatic transmission to be warmed up after a long drive and have the engine running in Park or Neutral when checking it. This is different than engine oil where you want the engine not running for a few minutes beforehand. Some automatic transmission dip stick do have cold markings, but still need the engine to be running.
#18
Old 11-21-2017, 08:50 AM
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Problem

Hey all,

I would like to ask you - (I unintentionally overfilled the engine with oil) could it be the reason why my engine is weird?
Symptoms: shaking much more than usual, doesn't sound the same, doesn't properly accelerate even more so /proportionally/ with rising RPM.
And is lightly(very lightly! almost unnoticeably) smokey.
Additionally, my coolant fluid is below minimum although my engine temperatures are fine.

I haven't driven the car anywhere yet as it's acting so weird and I don't want to destroy anything on it. I'll release some oil of it soon to make it to Max.

It's an old Mazda 626 2.0 2001 with 270K(km) / 170K miles

Last edited by sano262; 11-21-2017 at 08:51 AM.
#19
Old 11-21-2017, 09:09 AM
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Quote:
Originally Posted by sano262 View Post
Hey all,

I would like to ask you - (I unintentionally overfilled the engine with oil) could it be the reason why my engine is weird?
Symptoms: shaking much more than usual, doesn't sound the same, doesn't properly accelerate even more so /proportionally/ with rising RPM.
And is lightly(very lightly! almost unnoticeably) smokey.
Additionally, my coolant fluid is below minimum although my engine temperatures are fine.

I haven't driven the car anywhere yet as it's acting so weird and I don't want to destroy anything on it. I'll release some oil of it soon to make it to Max.

It's an old Mazda 626 2.0 2001 with 270K(km) / 170K miles
yes. if it's way overfilled the crankshaft is sloshing oil around, it may not drain back from the cylinder head fast enough which can cause oil to get past the valve seals. Also the crankshaft may be throwing excessive oil up onto the cylinder walls and getting past the piston rings.

Drain it all out and try again.
#20
Old 11-21-2017, 09:10 AM
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How much over? I would also top up your coolant as well. What colour is the smoke? If it's blue you're burning oil, if it's white-ish you may be burning coolant.
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#21
Old 11-21-2017, 09:31 AM
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At 170K miles, I would suggest a complete tune-up ... change everything that needs to be changed regularly ... jz78817 mentioned valve seals and piston rings, if you haven't replaced these then they're probably shot anyway, the extra oil is just making the problem worse ...
#22
Old 11-21-2017, 03:10 PM
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Quote:
Originally Posted by sano262 View Post
I would like to ask you - (I unintentionally overfilled the engine with oil) could it be the reason why my engine is weird?
Yes. Based on the fact that you overfilled it combined with the symptoms you list, I would say you need to drain the oil and fill it again to the proper level, NOW.

If you have too much oil, instead of draining down into the oil pan it gets up into the moving parts of the engine and gets whipped into a froth. When you have frothy oil, it doesn't flow where it should, and it's basically about as bad as having no oil at all. If you haven't ruined your engine already, you are in severe danger of ruining it if you continue to drive it. So get this taken care of ASAP.
#23
Old 11-22-2017, 10:07 AM
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Back when I drove race cars at a local short track, we ran the engines 1/2 to a full quart over the full mark. This was to keep the oil pickup in oil during hard cornering and acceleration. We ran stock engines and were not allow dry sump oiling systems that are used on most racing engines. The only engine I ever had a problem with running over full was a 350 Buick engine. Removing the oil pan and adding a home made windage tray solved the problem of the oil getting whipped into foam by the crankshaft.
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