VEvolution

Does oil in the oil pan have a "shelf life" expiration time? Yeah, I know oil on a shelf doesn't, and I also heard oil hanging out in an oil pan for too long will eventually build moisture within itself if I remember correctly. And the time for that was about 6 months.. Is this true? If not, about how long can you safely keep oil in a pan? Cause I know people using synthetic for example don't even do over 5k a year on their oil, so is it okay for them to do an oil change once a year? Could they even wait 2 years?

chrome91

iTrader: (1)

IIRC for the most part oils life is gone after around 5 months, i usually dont hit the 3000km intervals so i change my oil every 4 months and i use synthetic. you could maybe wait longer but for how little of a bother doing a oil change is i dont care lol

VEvolution

5 months even for synthetics? I heard they are more resistant to moisture. It's just my car takes 7 quarts($$$), and I'd like to change it once a year if I could.

I think I will change it before the winter, and send it out to blackstone labs and see what they tell me about it. Better not find no coolant in there lol

asand1

iTrader: (1)

As long as you drive long enough distances, moisture wont be a problem. The engine heats up an moisture is driven out via the pcv. What you need to wiry about is acids building up from unburned hydrocarbons.

VEvolution

Hm, good info. How long do you think those acids need before they start causing damage?

iDuty

Are we referring to engine oil sitting in an unused vehicle? If so, its shelf life is long enough that the vehicle will have much bigger problems from sitting than the oil.

If you are driving very short trips every day and no long trips, especially in the winter, then you get accumulation of moisture and gasoline from the engine running cold most of the time. Both of those contaminants shorten the life of the oil.

If you're accumulating miles slowly simply because you only drive once or twice a week then I would not hesitate to use the oil for a whole year.

VEvolution

I was referring to used and unused.. Didn't really matter. Just wanted to know how long you could leave the oil in there as long as your not passing the 5k mile mark for synthetic and 3k mark for conventional.

talkinghorse

iTrader: (121)

The OEM's oil change recommendation is typically miles or time (e.g. 3750 miles or 6-months) whichever comes first. As pointed out above, condensation will accumulate in the crankcase and form acids and corrosion. The additive package in the oil neutralizes the acids and combats this process.

As with petroleum oils, all sythetics are not created equal and unless the oil you are using is specifically formulated/recommended for extended service life (e.g. AMSOIL which contains a more robust additive package and carries a 1-year max life) I would recommend you not exceed the OEM's time recommendation regardless of your mileage.

T_Behr904

Synthetic oil can be safely kept and used in a car for 2 years, not including mileage. Porsche for the last few years with their DFI (direct fuel injection) has their service intervals of 2 years/20,000 miles, or whichever comes first, or when the car tells you it's time for service. Before that with the non-DFI, it was 1 year, but can't recall the mileage, or whenever the car tells you it's due. The non DFI cars service intervals were then called an "annual service" since in most cases it only had to be done once a year.

The main reason for the longer service intervals is because synthetic oil doesn't break down and lose it's viscosity as quickly as non synthetic oils. Most auto manufacturers now that use factory fill synthetic oils have these new extended time/mileage service intervals.

nibs

I think you are best following the recommendation of the manufacturer or company that makes the oil. Most synthetics on the market in the U.S. are not really true synthetics anymore, but hydro-cracked oil that came out of the ground, just like normal oil.

Nissan's recommendation is 3 months for severe service and I think not being driven often is severe service. Cars are made to be used, not to sit around.

If I were you I would follow the little table below. I used Mobil & Amsoil products as comparison points only. I'm sure other oil manufacturers also recommend time-based drain intervals, and you should be able to find them if you look.

Conventional: 3 months (or miles)
High Quality Conventional: 6 months (or miles) [Mobil Super is guaranteed for oil changes up to 6 months.]
Normal Synthetic: 3 months (or miles)
Better Synthetic: 6 months (or miles) [Amsoil XL says is good for 6 months / 10,000 miles. Mobil 1 Super Synthetic is is 6 months / 7,500 miles.]
High Quality Synthetic: 1 year (or miles) [Amsoil Signature Series 12 months / 25,000 miles. Or Mobil 1 Extended Performance 12 months / 15,000 miles.]

nibs

I think you are best following the recommendation of the manufacturer or company that makes the oil. Most synthetics on the market in the U.S. are not really true synthetics anymore, but hydro-cracked oil that came out of the ground, just like normal oil.

Nissan's recommendation is 3 months for severe service and I think not being driven often is severe service. Cars are made to be used, not to sit around.

If I were you I would follow the little table below, without a used oil analysis. You seem to be a good candidate for a UOA, as I imagine you would be able to get more than the manufacturer's recommendations in terms of months. Mobil & Amsoil products as comparison points only. I'm sure other oil manufacturers also recommend time-based drain intervals, and you should be able to find them if you look.

Conventional: 3 months (or miles)
High Quality Conventional: 6 months (or miles) [Mobil Super is guaranteed for oil changes up to 6 months.]
Normal Synthetic: 3 months (or miles)
Better Synthetic: 6 months (or miles) [Amsoil XL says is good for 6 months / 10,000 miles. Mobil 1 Super Synthetic is is 6 months / 7,500 miles.]
High Quality Synthetic: 1 year (or miles) [Amsoil Signature Series 12 months / 25,000 miles. Or Mobil 1 Extended Performance 12 months / 15,000 miles.]

SilverMax_04

This is a good question, and the replies in these posts above are fairly accurate:
4, 6, 8, & 9.

I worked for an oil company for 35 years and know a little about this topic - I retired in 1998. We need a little history and a little science to understand why motor oil has a life - why it needs to be replaced and when.

Before about 2002 or so (I don't know the exact year, but this is close), the federal government had a fairly lax standard for the sulfur content of gasoline, and some gasoline was (relatively speaking) loaded with sulfur - because there is sulfur in most grades of crude oil and it takes refinery processing to remove it. That year the government mandated an extra-low sulfur content for gasoline sold in the USA (some very small refineries in the Rocky Mt area were given some extra years to meet this tighter specification). Because of this mandate, refineries had to build new de-sulfurizers or expand their existing units. It is the sulfur in gasoline that is the major culprit that causes acid to build up in the motor oil. Lets look at the chemistry of that build up.

When a gallon of gasoline is burned in your engine the combustion process produces almost a gallon of water - most of which goes out your tail pipe as water vapor. (You may have noticed that your muffler and tail pipe have a longer life than they did before ultra-low sulfur gasoline. This is the major reason they last longer, although some car companies have improved their quality as well.) The combustion does not burn the sulfur, and it ends up in the water vapor. When your engine is cold, this vapor can condense in your engine and some of it ends up in the motor oil in the sump below your engine. The additives in the motor oil are designed to neutralize this acid - until they are completely used up doing their job. If your engine gets hot enough and stays hot enough long enough, the water in the motor oil will evaporate - reducing the volume of acid. However, the sulfur does not leave when the water evaporates. Less water is good, but higher concentrations of sulfur are bad. But extra low sulfur gasoline is the major improvement in all of this. (There are very little unburned hydrocarbons that get to your motor oil - the gasoline evaporates much faster than water. If any gasoline does get there, any sulfur in the gasoline will still be in the motor oil when the gasoline evaporates - but this is very minor.)

Well, with extra low sulfur gasoline, there is much less sulfur than there had been in the past - thus less sulfur to form acid in your motor oil. Although the oil companies and motor oil companies knew this fact, none of them made it widely known. They wanted you to continue to change your motor oil every 3 K miles or so - so they could sell you more product. I don't know why the car companies have not picked up on this gasoline fact, although the discussion above about Porsche may be an indication that some have - as well as Nissan setting a maximun OCI (Oil Change Interval) of 7,500 miles.

As nibs points out in his post, you need a "used motor oil analysis" to really know what condition your motor oil is in when you change it. Or you can simply continue to change at 3 K mile intervals and not worry - except for the very likely good quality oil you are discarding. And generally speaking, the color of the used motor oil is not a good indication of its condition.

While my Nissan warranty was in effect, I changed oil at their maximum OCI of 7,500 miles. Since my Nissan warranty ran out due to both time and mileage, I have been changing my synthetic motor oil every 10 K miles or so and getting an anlysis of that used oil from Blackstone Lab. The lab tells me I can safely run my oil longer than this, but I don't like to run a quality oil filter past this mark - and don't want to change filters without changing oil. Here are the comments Blackstone gave me when I changed last fall with 113 K miles on the Max after pushing the oil and oil filter to 12.3 K miles:
"Thanks for the note that you'll be switching oil brands. You have a nicely wearing engine so just about anything you can find on a store shelf should work for you. You could try whatever ends up to be on sale wherever you're shopping, and it wouldn't even have to be a synthetic. Even with the cheapest brand you can find, you'll probably still have no problems running 12,000 miles (or more) on your oil. At any rate, we only bring this up for lack of other problems to talk about. Your engine is wearing like a champ and the TBN is still fine at 3.0. Try 14,000 miles."

I will not go longer, and will probably go back to about 10 K miles when I change oil this fall. So, on a time basis - I don't pay any attention to time - I am changing oil about every 10 to 12 months - no problems. Also, in addition to the additives to combat acid, you still want the motor oil to properly lubricate your engine - and even systhetic motor oil will eventually break down and not lubricate as well.

You may wonder why I spend money at every oil change (about once a year) for a lab analysis. The answer is my Dodge pickup truck. The first analysis I had done on this truck showed there was antifreeze in the motor oil. Turns out there were cracks in both heads that were allowing the antifreeze to leak into the motor oil. A lab analysis is cheap compared to replacing the whole engine. All I had to do, because I caught this problem in time, was to replace both heads.

I've rambled on about this topic long enough. Oh, the oil change the lab mentioned is changing from Mobil 1 10W30 to Pennzoil Synthetic 10W30. I had a lot of Mobil 1, but eventually used it up. And after buying the Mobil, I got a real good price on the Pennzoil and stocked up on it.