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I had an engine shudder during my idle after startup yesterday morning. I checked my oil level and was a full X cross hatch height below the min oil line. I added 1.5 qts to get up to the max line. It made me curious how low does the oil have to go before the oil light comes on? Seems like I was 0.5 qts below min.

UPDATE: the engine shudder was ultimately due to a clogged PCV hose that got replaced.

  • I downvoted all three answers because they are dealing with the oil pressure light while in the title you specifically asked about the "low oil light" (which not all cars have, e.g. i.stack.imgur.com/4hpyr.png). If you actually meant the oil pressure light (which all cars have, e.g. i.stack.imgur.com/kQ7oC.png), you should say so. – AndreKR Sep 28 '17 at 12:19
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    I meant the oil can symbol in your second linked image; but the question was flawed by my understanding of what triggered it and what it actually represents. @JPhi1618 caught and explained the subtlety. I was previously unaware of the three oil related indications/measures you might find in a vehicle: level, pressure, and temp. – jxramos Sep 28 '17 at 18:15
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    Yes, Question Askers get grilled for not already knowing everything there is to know before they ask the question. Not exactly sporting, is it? In this case, the Answerers took a beating as well, through no fault of their own. Great. – user29824 Sep 28 '17 at 18:21
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    On my BMW there is a single light that is either orange or red. The orange indicated low level, and happens at 1 qt. low reliably. The red light comes on when the oil pressure is low, thankfully that only came one once when the sensor was unplugged. But the light worked! – Ukko Sep 28 '17 at 19:05
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    @nocomprende - that's why it's good when askers give the make/model of their car, then those that answer can give more specific answers like "In your XXX car, that light warns you about oil pressure, but in some cars (like YYY and ZZZ), there's a separate warning for oil level" – Johnny Sep 28 '17 at 23:54
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The approximate answer for the cars that I have driven that take the standard 5-6 quarts is "about 2 quarts low". Maybe more, maybe less. Normally, you'll notice the light come on when taking a sharp corner as the oil sloshes to the side and the oil pump sucks air for a second.

But, the major point here is that the light means "low oil pressure", not just low level. That's important because low pressure means oil is not pumping through the engine properly, and serious damage isn't far behind after that. When the oil is too low to cover the pick-up tube from the oil pump, it sucks air, resulting in low pressure and "less than optimal" engine lubrication (to say the least).

If you see the light come on when taking a corner, find the nearest place to buy oil and add it. If you see the light come on when driving normally, pull over and turn off the engine as soon as safely possible. Don't drive the car until oil is added.

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    What the light may mean actually depends on the vehicle. I have an oil level light and an oil pressure light on my Subaru Legacy. – Ellesedil Sep 28 '17 at 4:19
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    @Ellesedil that’s cool to know. I haven’t seen an oil level light so I assume they are more rare, but neat to know it’s in a Subaru. Thanks. – JPhi1618 Sep 28 '17 at 4:54
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    @Ellesedil good to know that someone has expanded the detection beyond a single threshold. With all the other sensors proliferating in newer vehicles I've never understood why the oil one hasn't gotten a ubiquitous you need to check your level more frequently because you have a minor problem level that would fire when the engine needed a significant topup but was nowhere near the catastrophe level and then split the existing one into low pressure add more asap and no pressure stop the engine immediately levels. – Dan Neely Sep 28 '17 at 15:22
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    @DanNeely "Check Engine" light? Covers all cases. – user29824 Sep 28 '17 at 16:04
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    @DanNeely I guess we need some kind of a screen which would clearly explain what is going on. Nah, then I would not have to go to a shop and pay $200 just to have the fault code read by some expensive proprietary machine that only shops can afford! It would destroy the entire economy! – user29824 Sep 28 '17 at 16:38
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Typically, the oil light does not indicate a low oil level, but low oil pressure! Meaning that the anwser as to how low your oil level would have to be before the light turns on, would be "too low!".

  • Wow, that's a very different interpretation from what I was guessing; so it sounds like there's no direct relation to the min and max levels etched on the dipstick I take it then. – jxramos Sep 27 '17 at 19:18
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    Thats why some trucks have a light, an oil pressure gauge, an oil temperature gauge and an oil level gauge which is just like a fuel tank gauge .... – Solar Mike Sep 27 '17 at 20:02
  • This is not true of half the engines I've taken apart. You're right that low pressure is a sign if imminent failure, rather than an early warning (but I don't think that is easy to read from your answer). – Sean Houlihane Sep 28 '17 at 9:49
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    It might be useful to expand on your answer a little bit. The purpose of the light is to warn people that the engine will be destroyed if they don't act within a few seconds, not to warn them that they will be stranded if they don't act within a few days. – supercat Sep 28 '17 at 15:52
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    @supercat every car should have a warning label: "This car will fail and leave you stranded, if you drive it or own it long enough." It should be next to the label that says "All disk drives eventually fail. Make backups." (And the obligatory one: "Hot beverage may be hot.") I like the one for humans: "We're all gonna die!!!" – user29824 Sep 28 '17 at 16:02
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It really depends on the car. My MINI Cooper doesn't have a low oil light, just a low oil pressure light. My engine was 3 quarts low and the light hadn't come on yet (and it only holds 4.5 quarts!).

  • Maybe you need a warning light that the oil light was burned out? – user29824 Sep 28 '17 at 12:27
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    I just wish BMW gave me a readable dipstick that could be checked when the engine is cold. Everything in this car is needlessly complex. – Spivonious Sep 28 '17 at 13:25
  • mine was 3 quarts low too and still no light. I am worried my engine is ruined. Was your car okay after that? – S Perry Jul 20 '18 at 21:11
  • No problems yet. It was making such a racket that I didn't push the engine too hard while it was low. It was low for about 1000 miles. – Spivonious Jul 22 '18 at 17:27

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