Does oil go bad?

[btan219]

I drive 3k-3.5k every 6 months, my daily driver, no track or racing. Does oil go bad? I'm wondering if I should change it every 6 months regardless of how little I've driven, or can I change it at 5k even if it takes a year to get to? I check my oil level often, but I'm wondering if it's still a good amount after 6+ months if I should hold off on changing the oil.

[JD001]

I manage about 2.5k a year, its serviced once a year and that's it. The big issue I had was that the original battery just couldn't keep a charge, all changed when new battery was installed under warranty.

[Tcoat]

It has to be changed at the time or mileage interval whichever comes first in order to maintain warranty.

I have always thought the time interval for cars is a bit of a scam nowadays. Way back in history when they still used actual oil it could indeed lose some of it's properties just sitting in a car. The modern synthetics will stay good forever if not use or contaminated in some manner.

Follow the schedule until warranty is up and then change at the appropriate mileage.

[nikitopo]

Originally Posted by Tcoat

It has to be changed at the time or mileage interval whichever comes first in order to maintain warranty.

I have always thought the time interval for cars is a bit of a scam nowadays. Way back in history when they still used actual oil it could indeed lose some of it's properties just sitting in a car. The modern synthetics will stay good forever if not use or contaminated in some manner.

Follow the schedule until warranty is up and then change at the appropriate mileage.

Never thought of this. I am still under warranty and the dealer changes the oil every year. In the last service the oil had just 1k miles and the dealer changed it. When the warranty is over, I'll keep the oil longer ...

[mav1178]

If you are not testing your oil on a regular basis, then the answer is yes, they do "go bad". They don't suddenly break down but oil health is like bloodwork, it tells you a lot of detailed info about the health of your engine internals.

Oil change intervals should be lengthened only with the use of oil test results that have a known time or mileage interval... otherwise you're just making good guesses with no basis in fact. You should swap out the fluid if you're even under recommended mileage intervals, because you have no way of knowing how much additives were consumed already up to that point.

[Tcoat]

Originally Posted by mav1178

If you are not testing your oil on a regular basis, then the answer is yes, they do "go bad". They don't suddenly break down but oil health is like bloodwork, it tells you a lot of detailed info about the health of your engine internals.

Oil change intervals should be lengthened only with the use of oil test results that have a known time or mileage interval... otherwise you're just making good guesses with no basis in fact. You should swap out the fluid if you're even under recommended mileage intervals, because you have no way of knowing how much additives were consumed already up to that point.

Much of that depends on how you are using the car. Not many people get analysis done. Oil sitting in an undriven car is not any different than oil sitting in a jug. It is not breaking down until the car is running. Swapping out early based solely on a set period of time has no real advantage. Test or no test the oil needs to be used to break down. Now of course changing early doesn't hurt anything either.

[Ernest72]

Fuel dilution can happen over time, small amounts of fuel get into oil and you can lose viscosity. I would change every year for sure. Even every 6 months cost nothing.

[Overdrive]

^^^ This is true. While I get where Tcoat is coming from, the oil doesn't just drop back into the pan unchanged, but it also isn't going to get completely broken down from fuel and water sitting in it. Fuel and water sitting in there long term can wear the oil down over time while the car sits, but it'd have to be a really long time to really break it down. It's not going to turn it into useless sludge in a year, but in the case of the OP's car, you're basically a low mileage case even with daily driving. Is that due to short trips? If so, the oil probably isn't always getting up to operating temp, and that can eventually cause issues by not burning off the moisture and fuel that gets into the oil. Again, is it going to kill the car in six months or a year? No, but you wouldn't be doing the car any harm changing the oil once every six months or once a year given your low miles for a year. What you drive in a year I do in less than 6 months, so I'm pretty much bound to change out my oil twice a year because I drive a lot. You could, as cheap insurance, just change out the oil filter at six months, then the oil and the filter after a year's time. The way our filter is oriented you can swap it out easily without making a mess or having to really top up your oil level as you would in other cars. Just the same, changing it out every 6 months, especially if you DIY and keep receipts for your parts for any warranty purposes, is still cheap insurance that you'll always have fresh oil. You could also send samples of your used oil to a place like Blackstone Laboratories and find out how your oil is doing in your low-mileage case. If it's still in good shape after 6 months, you could go longer before having to change it.

Oil doesn't really break down in a year's time unless it's put through some really heavy use, though. You can be sure the jugs you buy in the store weren't bottled yesterday, and probably spend several months just sitting in warehouse storage before they spend another potential several months on store shelves waiting to be bought. In your car they certainly won't last forever, but won't go bad to a dangerous level in a year's time either unless you're doing track days in sandstorms on 120 degree days as a part of that 3,500 miles of driving you do.

[Tcoat]

Originally Posted by Ernest72

Fuel dilution can happen over time, small amounts of fuel get into oil and you can lose viscosity. I would change every year for sure. Even every 6 months cost nothing.

If you are getting that much fuel in your oil when driving 6k a year you have bigger issues than an oil change.

[Overdrive]

Exactly. It's a valid concern, but more like one you should have when someone barn-finds a BRZ Series.Blue in 40 years......of course by then the price of an oil change and a tank of gas will probably each have a comma in them.

[nikitopo]

Originally Posted by Overdrive

of course by then the price of an oil change and a tank of gas will probably each have a comma in them.

There are many more oil & natural gas reserves than we might think. The issue is that the big energy companies are extracting the ones that have currently the lower cost and other political reasons. When these reserves will gradually drain out, companies will move to the other (known) reserves. There might be a price increase, but there is no way to have a comma between.

[Overdrive]

...It was a joke? Goodness...

[Ultramaroon]

Originally Posted by Overdrive

...It was a joke? Goodness...

Jokes are different in a galaxy far, far away.

[humfrz]

Originally Posted by btan219

I drive 3k-3.5k every 6 months, my daily driver, no track or racing. Does oil go bad? I'm wondering if I should change it every 6 months regardless of how little I've driven, or can I change it at 5k even if it takes a year to get to? I check my oil level often, but I'm wondering if it's still a good amount after 6+ months if I should hold off on changing the oil.

Well, yes, the long chained hydrocarbons can be broken, if your engine temperatures reach above about 1,400°F .....


humfrz