Does motor oil go bad sitting in a can on the shelf?
#16
#17
Join Date: Feb 2002
Location: Greater Austin, Texas
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I'm a chemist, but not an oil chemist, so this has me curious - why is it recommended to change oil every 3k miles OR 3 MONTHS? If it doesn't go bad over time, why not just every 3k miles, even if they are spread out over 10 years?
#18
That is mostly intended to sell more oil. I've been changing the oil in my vehicles every 5K miles for 20 years and never had an engine failure. However, once the oil is in your motor and exposed to the combustion gasses, the additives do break down over time. Sitting in the can is completely different.
I put on about 1,200 - 1,500 miles a month, so when I was running natural (non-synthetic) oil I changed oil every 3,000 miles, even though I was spreading those miles between two different vehicles and it took 4 - 5 months for either one to hit 3,000.
By the way, back to the zinc additive, I've heard the reason for removing it was that it hurt the life of catalytic converters. Something that might be worth considering before running it in roller tappet engines.
#19
but I'm no chemist, just an armchair internet jockey
#20
I picked up a partial bottle of full synthetic SuperTech oil the other day that had been sitting on a shelf for probably a year. In the bottom it looked almost like mayonnaise had separated from the oil. According to what I've read from - Bob is the Oil Guy - Bob is the Oil Guy SuperTech is as good as any "regular" synthetic. This separation is making me wonder.....
#21
#22
That lower left pic is after I shook the hello out of it. It's going into the waste oil unless I decide to set it back and see what else happens to it.
#23
Yes, that's why lots of short trips are hard on oil. The heat/cool cycles are where you get the condensation. An engine just sitting there for 3 months doesn't do that much (if at all). Oil just sitting in an engine doesn't go bad either.
#24
It is the oil that determines ratio, Opti is one of them that recommends about a 70 - 1 mix. This is tough to get used to at first. Using it for years now. This way avoids having to keep two or three cans in the garage with two or three different mix ratios for lawnmower/snoblower/etc
The Amsoil stuff is at 100-1. Seems spooky using oil that thin.
#25
#26
Just got a new Stihl chain saw. They are doubling the warrantee if you buy a 6 pack of their synthetic at the time of purchase. They are calling for 50-1, but still seems weak. I guess if the manufacturer will tell you that.
#28
Personally in my vehicles that I only put a few hundred miles on over a course of a year. Not enough for an oil change per miles but overdue per "timeframe" And I still run them without changing the oil.
Cost you a little more in the extra oil used.
I don't run anything higher than a 40-1 regardless if they say it's ok.
Mainly because a mix of older and newer chainsaws so I just mix it at 32-1 for peace of mind. I run synthetic too so I'm probably pissing money away but it's better than a seized jug in my saws.
Its keeps the bugs away too sometimes
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