When checking your oil and it is not at the top of the stick where it should be for “full” how low down on the stick should it before you add oil to top it back off to full. There is that “area” on all dipstick range wise and wondered should it be in that area or not worry about it till it’s below that marked area.
Just add enough to bring to the full mark and find something else to worry about.
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There is a full line and an add line. Let it go down to the add line. On most cars, you then add one quart.
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It’s perfectly safe to let it go down to the FILL line. That’s what the line is there for.
I’m OCD about it, so I bring it back to the FULL line when it gets about 1/4 to 1/2 qt. down, but it isn’t necessary. I’m retired and have little better to do. 
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I put in a quart when it’s at the ‘quart low’ mark.
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The difference between the Full and Add marks on the dipstick is ONE QUART. That’s by design to make it easy for owners to check and add when necessary. In metric countries it is one liter.
When you stomach is half empty at 3 pm there is no need to eat half a meal; wait till 6 and have a whole meal!!!
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Don’t need 1/2 meal. That is why Cookies, Cake and Donuts were invented.
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I do the same as mountainbike does, but–as he said–if the OP wants to allow the level to fall all the way to the “add” mark, that is okay.
Just don’t let it fall below the “add” mark.
Just my 2 cents but I’m of the opinion that the oil level should always be kept at the FULL mark.
If you’re driving around one quart down on a 5 quart capacity car that means you’re 20% below normal. That in turn means the motor oil is taking a much more severe beating which in turn can lead to the oil having more of a tendency to sludge, oil consumption issues, etc.
Getting rid of heat from the motor oil is why some cars (SAABs, some Mustangs, police Crown Vics, etc) have external oil coolers.
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LOL, well said, my man. 
okay works for me, my follow up question is does oil type matter? I am referring both to like 5W30 over 10W40 and whose on the label. Is generic store branded oil just as good as the more expensive “name” brand? My car says use 5W30 which I ususally do but my dad has some 10W40 in his garage for his car which he doesn’t have anymore and wondered would it hurt to use it to top it off? Also what is the shelf life for oil be it opened or not?
Use what’s specified for your car. And I’m happy paying a bit more for the name brand. Cheap insurance.
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Generally, the bottom line is the “add a quart” line. As long as the oil is above that line, you’re fine. It doesn’t have to be at the top mark. Anywhere between them is safe.
If you insist on always having enough oil to be at the “full” mark, you’re going to have to experiment to figure that out for yourself by adding a little, checking it, and then repeating as necessary.
I use store brand oils in my car. They meet the same API engineering specs (like SH or SJ), cost less, and do the job just as well.
As for oil viscosity, the easiest thing to do is use whatever is printed on the oil cap and/or the dip stick. However, if you want to deviate from that, you should check your owner’s manual or shop manual to see if it has a chart similar to this one:
Based on this particular chart, the best oil to use for this particular machine (a 2003 Honda Nighthawk 750 motorcycle) in all conditions is 10W-40, but if I lived in Canada, 10W-30 would be fine, and if I lived in Key West, 20W-40 or 20W-50 would also be fine.
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There is much more to this situation than “just” the oil viscosity.
Even more important than the viscosity of the oil that you buy is its API service classification.
The newest classification is “SN”, but a somewhat older vehicle may have originally called for oil that fit the “SM” classification, or possibly even the “SK” or “SL” classifications.
These classifications have to do with both the lubricating quality of the oil and its detergent levels.
It is a good thing to go “up” in classifications, but one should NEVER go “down” in classification when it comes to the oil that you put in your engine.
If you go to a legitimate store nowadays, it is likely that you will find only “SN” specification oil, but “dollar stores” frequently sell oil with old, superseded specifications, and in fact last year, the Attorney General of NJ seized oil that dollar stores were selling which was of the “SA” classification. 
The “SA” classification was intended for engines made in the 1920s, and using that CRAP in a modern engine would be a sure way of destroying its bearings and other friction surfaces.
So–if your father has been hoarding that oil for a few decades, make sure that you look for the API service classification on the bottles, and make sure that it is AT LEAST equal to the API specification that your mystery vehicle calls for.
Read this for a wealth of valuable information:
http://www.pqiamerica.com/Labels.htm
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For me it depends. I really can’t remember when I let the cars get down to needing a full quart. Usually if it gets down to needing one half quart (pint) I will add that but it depends on how close I am to an oil change and if a longer trip is planned. I’d never start a trip down 1/2 or more. Now on small engines, keep those puppies at the full mark always.
Yes, I should have added exactly what Bing stated, to my earlier comment.
While I tend to be rather obsessive about the oil level, if I am going to have the oil changed in a week or two, I will just…let it ride…at 1/2 qt below the full mark for the limited amount of time remaining before the oil change.
I just picked up some motorcycle yesterday, and the conventional oil was API SF/SG/SJ. The synthetic oil that cost twice as much was API SH.
Bertrand, this is a vehicle that you want to trade as soon as possible so what does it matter what oil you top off with? If the oil container is unopened the shelf life is really long. Go on and mix the oil, the car will never know the difference.
Beware of oil that doe not meet your specs.
Lawsuit: Dollar General motor oil not safe for cars newer than 1980s
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