How long does synthetic last if the engine is not run??

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May 15, 2004
I have a car that I only drive 200 miles a year. I put fresh Mobil 1 10W-30 in it 18 months ago and have driven about 300 miles since then. How long can I safely leave this in at this rate. Should I change the oil at some point just due to age?

I know I could get an analysis done, but I'd like to know more about the theory of deterioration of oil and additive packages and how that affects shelf life.

You're probably good to leave it in all year. Even though it isn't necessarry, you may want to change the oil just to keep the drain bolt from sticking :-D

I hope you crank that engine every 2 weeks and run it or store it properly... I've found many engines tend to not like sitting up for long periods. What kind of vehicle is it?
Pour Point additives (cold weather flow enhancers) can be steadily depleted simply due to exposure to cold temperatures, but I would guess that your engine is otherwise just an oversize "bottle" that won't deplete or contaminate its oil significantly when the engine isn't run. But condensation inside the engine brought about by simple ambient weather/temperature changes can slowly contaminate engine oil as well, leading to acid build up. But once again, with only 200 mi/yr, these processes are basically neglegible for you. I'd probably take an opposite approach in oil choice. With only 200 mi/yr, I'd pour in the cheapest name brand "SL" oil I could find and change it out once/yr or 18 months. To say that ANY oil put in that ride is not being stressed would be the understatement of the year. Your biggest problem in my opinion would be tire flat-spotting, something I've dealt with in the past. Drive it, put it on jacks, or roll it 18" every month. And as Dominic suggested, engine oil seals sometimes harden from lack of driving. Curious...what kind of ride is this?

[ May 16, 2004, 09:26 PM: Message edited by: TC ]
Fortunately a synthetic has less pour point additives than a dino oil would. Most likely doesn't have or need any at all.

You would be very safe changinf out annually. Send a sample in for analysis at two years and you will probably find the oil still usable.

[ May 16, 2004, 11:19 PM: Message edited by: mormit ]
I'd like to have more info before recommending anything. Does the car sit in a closed garage in a mild climate? Or does it sit out on the street a block away from the ocean, in a widely varying climate?
I think the real ? is what is the nature of use when you do drive it? Is it leisurely driving, or hard, heavy foot driving?

When you do put the 2-300mi on, is it done in ALL trips over 15-20 miles? If so, the oil most likely gets up to full temperature, and condensation will evaporate out. If no, and its on shorter cruises, Id beware of acid formation, and change it more often.

You might want to consider a HDEO diesel spec oil, which has more basic reserves (prvided your engine will take a 5w-40 or 15w-40 oil OK).

When you do drive it, make sure you get up to full operating temp and at least drive for a few more miles after that. That should burn off all the crap produced at startup and while running before it heats up.
I use M1 10W-30 in my 90hp Honda outboard and change every 50 hr. That is typically 18-24 months. The UOA results have always been stellar with the oil suitable for continued use. So I wouldn't worry at all. Particularly if your occasional use gets the oil hot enough to drive off moisture.
Thanks for the input so far.

The car is a 1984 Volvo 245T - 2.1 liter, 4 cylinder, intercooled turbo.

Whenever the engine is started, it is never run for less than 30 minutes. It has an oil temp gauge and I use it to ensure 180 - 200 degrees is reached and sustained for at least 10 minutes. It is usually started and run for 30 minutes every 6 weeks or so, even if not driven. The car is always stored in a garage near Washington DC. We have hot summers and coldish winters.

When it is driven, it is usually highway miles, some heavy foot.

I know I can leave the oil in all year, that goes without saying. What I am wondering is, is once every three years (750 road miles plus several additional hours of idling time) about right? The oil is always Mobil 1. The filter is always factory (made by Mann). Those are non-negotiables.
Given the info you provided above, I can't think of a reason why it wouldn't last 2 years, maybe 3 years. What the heck, go 3 years and do a User Oil Analysis at that point. With so little use, I don't see how you could do much damage to it. The UOA should indicate if your plan is sound or not.

Maybe someone who has many collectible cars would have more experience with your situation than I do and could provide better insight.
only thing you have to be careful of is the pH of the oil, if it is too basic, it can destroy seals. I dont think M1 has that problem, I know pennzoil does when in storage..

Originally posted by Durrr:
only thing you have to be careful of is the pH of the oil, if it is too basic, it can destroy seals. I dont think M1 has that problem, I know pennzoil does when in storage..

I left M1 5W-30 in a car for 22 months and the TBN was still 8.5. I'd say it's safe in that respect...
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