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Synthetic lubricants, rarely driven AWD -- how long?

I drive the Subaru 2003 maybe 800-1400 miles per year, on a few long trips up to the mountains. Bought the vehicle used with 20k miles, when it was 4 years old. Did the 3 year/30k mile service and put in Mobil 1 synthetic oil; synthetic transmission fluid (because it’s rarely driven but when used it’s freeway then half steep forest service roads in hot weather).

How long do these lubricants last?

Aside: Yes, I do have to get out the hand clippers to mow the grass around the tires! I don’t move the vehicle sometimes for literally months at a time. I do use a smart battery charger every month or so.

I recommend changing engine oil once per year, minimum, even with low miles driven.

As far as the other fluids go, I’d follow the “Severe Service” maintenance schedule that came with the car.

On the fluids besides the engine oil and automatic transmission oil, I would not worry much about your differential fluids especially with synthetic. I also would not worry much about (if) manual transmission fluid.

Read the owner’s manual. Make sure you read the part about Severe Service and that you remember that it list time and miles, which means which ever comes first.

I asked Subaru locally, and also asked a local performance shop that races Subarus. They agreed the manual’s intervals assume petroleum, not synthetic, and said the synthetic lubricants have better oxidation control and less volatility and should be good for much longer than the recommended (petroleum) intervals, but didn’t have an idea how long. So I appreciate the advice to follow the manual, but I’ll leave the question here a while.

I’m hoping someone knows of experience putting vehicles in ‘ready use storage’ (military, maybe) – or can recommend a lab that can test and compare to fresh Mobil 1. I’d rather find out than assume handling it like petroleum, as I have months til I’ll be using it again.

I do know to drain and replace the gasoline, by the way. Anyone know if any of the additives for that actually do any good to stabilize fuel?

No offense, I did RTFM and know the severe use miles/time; it’s because I found out that those assume petroleum products that I started asking about this.

PS, this is not directly relevant, but it’s the closest I’ve come to useful information so far:

(AOL has broken their file system so it’s not really there; you may be able to hunt up the PDF somewhere; I just used the HTML version available from a Google Scholar search result, see below; that omits some of the graphics but is readable)

Brief quote:

6. Inactivity - Motorcycles are typically used less frequently than automobiles. Whereas automobiles are used on a daily basis, motorcycle use is usually periodic and in many cases seasonal.These extended periods of inactivity place additional stress on motorcycle oils. In these circumstances, rust and acid corrosion protection are of critical concern.

It is apparent that motorcycle applications place a different set of requirements on lubricating oils. Motorcycle oils, therefore, must be formulated to address this unique set of high stress conditions.

The purpose of this paper is to provide information regarding motorcycle applications, their lubrication needs and typical lubricants available to the end user. It is intended to assist the end user in making an educated decision as to the lubricant most suitable for his or her motorcycle application.

The testing used to evaluate the lubricants was done in accordance with American Society for Testing and Materials (ASTM) procedures. Test methodology has been indicated for all data points, allowing for duplication and verification by any analytical laboratory capable of conducting the ASTM tests. A notarized affidavit certifying compliance with ASTM methodology and the accuracy of the test results is included in the appendix of this document.

This document reviews the physical properties and performance of a number of generally available motorcycle oils. …

(including Mobil 1. Found using this search:“Mobil+1”
(the blog software breaks at the first quote mark; cut and paste to use that)

Given your limited miles/synthetic I would change out the manual transmission and diffs oil every 3-5 years whatever makes you sleep better at night.

The manual is useless in this case as I believe severe is something like every 15k miles/15 months. However your driving does not resemble severe in my eyes especially given the lack of mileage. If you drive normally the spec only states inspect the fluid.

My family(direct, in laws etc) has 10 Subaru’s and four of them have 150k-200k with any differential oil changes. No differential or manual transmission failures and none have changed the fluids.

One clarification, my vehicle is a 2003 automatic transmission, basic Forester.
Yep, we do get the inspection done; the mechanics, though, don’t go past ‘looks and smells brand new, no surprise with so few miles’ – that’s why I’m looking for more.

We get many “I use synthetics,I use my vehicle very little, how does this affect my service interval” questions.

I feel people want to hear that their service interval is extended.

Who would you have to be,what would your education need to be,what tests would have to be performed to give anything but a opinion?

The question is easier in that it doesn’t involve denial of warranty.

I don’t feel comfortable giving any advice simply because I am not qualified.

The OP seems to have reasearched his concern and has himself gathered enough data to make his own call.

 Oil is cheap engines are not.  How much is it going to cost you to follow the instructions in the owner's manual?  Skip a cup of fancy coffee and follow the owner's manual.