Does motor oil "go sour" or have an expiration date?

[Tractor-Holic]

Saw a strange thing yesterday at my friends car repair shop--he was doing an oil change for a customer,and the guy brought in his own oil--some regular Castrol 5W-30 he'd had hanging around in his garage, for perhaps as long as ten years..figured he might as well use it up,no sense in buying more if you already have oil ,right??..we saw no reason not to use it--after all,who knows how long oil sits on a store shelf or in the backroom before it ever gets sold anyway??..I never heard of oil "going bad",or having a "use by" date ..

We were adding the "new" quarts of oil,which by the way were never before opened,the plastic seals on the lids were still intact--we noticed near the bottom of each oil can the last few ounces came out like it was gelled,and a darker color than the rest of the oil,which looked perfectly normal in every way!..we thought maybe it could be condensation,but it didn't appear to be water,it didn't look like mayonaise like water and oil does..

We thought "maybe it's just that one bottle"--nope,all 5 quarts did the same thing!...the cars owner was called over,and we had him watch as we added the last quart,and told him "just wanted you to see for yourelf WE didn't add anything BUT the oil YOU brought!..he asked if we thought we should flush that oil out and buy more new oil,but after he found out it is now over 3 bucks a quart,he said "screw it,I'll just run it and see what happens!"--he kept the empty bottles ,just in case he has to call Castrol with bad news!..these bottles had price tags with "1.29" on them,so that should tell you how old they were!..I'd guess around 1997??..

I have no clue what is the deal with that oil--looked like straight 50W at the end of each bottle,and like egg whites in consistency..maybe the additives and viscosity improvers settle out after many years??..should be interesting to see if any engine woes arise after he runs it awhile..so far it seems perfectly normal..

I always liked Castrol,used their 20W-50 for years in my vehicles, and never had any engine trouble whatsoever..when I see things like this,it makes me wonder...anyone else see oil "spoil"??..

Robert

[Bill Kapaun]

The "additive package" probably separated.
I think I would have shook the last bottle to see if it remixed OK.

[Tractor-Holic]

We did shake one of the bottles up some,and it still seemed like the goop at the bottom didn't want to mix well with the rest of the oil--but I'm sure after the crankshaft whips it around, and it goes through the oil pump gears a few zillion times,it will probably be "homogenized" again!..(we hope!)..

Robert

[bontai Joe]

Here is a link to some good info on oils, what they do, and about half way down, they discuss the shelf life of oil, (around 4 to 5 years under the best of circumstances):

http://www.carbibles.com/engineoil_bible.html

[Mr Jimi]

I use aged oil all the time, I shake it like I would a can of spray paint
No problems yet
Think about this ! If It did expire it would have a date on it like food or beer = no brainer

[comp]

the ten year old old wasn't tested like new oil so it wasn't up to todays standards
about the longest i have ever had any was a year so it wasn't a problem

[abner]

"The "additive package" probably separated.
I think I would have shook the last bottle to see if it remixed OK."

I agree with Bill. Gelling also can happen when incompatible oils are mixed: additive package chemicals react with each other.
I suspect the chemicals can break down over time also, and change the additive package makeup, separate then possibly gell. Just guessing here, though.

Joe