Following time or mileage interval for low mileage car?

[Ohio Enthusiast]

Since I bought my BRZ almost 6 months ago, I only drove it 1,500 miles. Obviously the COVID pandemic is a part of it, but even without lockdown I won't drive it that much.

Maintenance schedule is always given in miles and months. Obviously it makes sense as some items degrade with time, even without use (such as fluids and rubber parts), but I'm not sure if other items really require time based replacement. I'm specifically talking about air filters (cabin and engine), but I guess some other items would qualify as well, such as spark plugs.

In the US maintenance schedule table (from the shop manual), air cleaner element and A/C filter are due for replacement both on mileage and on months (30 months or 30,000 miles for the air cleaner element and 15 months or 15,000 miles on the A/C filter).

However, in the UK maintenance schedule table, although the air cleaner element is in the table under 36 months and 45,000 KM, a remark says "Replace every 45000 km". The A/C filter doesn't have such a remark, though, only asking replacement every 24 months or 30,000 KM.

Setting aside the differences between the US and UK/European intervals, does it make sense to replace a paper air filter based on time?

Just to be clear, I don't really care about the cost or convenience. I asking for a real explanation for this. I'll probably replace the filters based on time anyway, as they are simple to change and cheap to buy.

[Ohio Enthusiast]

Noticed the same for spark plugs - UK interval has a remark about replacing based on mileage only (66,000 miles), vs. the US interval of 60 months or 60,000 miles.

[skylinekin]

I would use months for things like fluids (incl. oil filter) if the car doesn't get driven much. Mileage is more appropriate for hard parts and filters like you mentioned, but the cabin filters and air filters are not really very expensive and easy to replace so its up to you? I think you will get a bunch of opinions in this thread, what do you feel comfortable with?

[thomasmryan]

oil will absorb moisture so i would drive it 30-40 minutes once a month to cook that off.

[JD001]

This year my car had its 6th year service, the "big one" as my service garage put it. My car has only done 13miles.. averaging 2.5k pa. This year less so, not used much due to the virus.

I get my car serviced every year as per the Subaru service schedule..

[nikitopo]

Originally Posted by JD001

This year my car had its 6th year service, the "big one" as my service garage put it. My car has only done 13miles.. averaging 2.5k pa. This year less so, not used much due to the virus.

I get my car serviced every year as per the Subaru service schedule..

Why only 13k miles? Are you comuting to work via public transport?

[JD001]

Originally Posted by nikitopo

Why only 13k miles? Are you comuting to work via public transport?

Yep, public transport and walking. Prior to using trains/buses I had company cars so again the mileage on my private car(s) was very little, weekends and holidays.

Since March I think I've done about 100miles, I don't envisage this going up much as we may face another lockdown.

[Spuds]

I do the regular service to include oil change tire, rotation, etc. every 6 months, along with inspecting most items in the checklist for wear. The major stuff like spark plugs will be by miles, unless something is wrong with them.

As for filters, I would just do them by miles. I have a reusable engine air filter so I just clean it at least once a year. I think I replaced my cabin air filter a few years ago, probably due for another.

[sygfrid]

We all know that the PMS is a GUIDE so that nothing is forgotten esp. for the non-car peeps. For more experienced motorists, we do them when deemed necessary (more frequently &/or earlier than what the sched says).

IMO, it's better to clean or even replace cabin filters yearly or even 2x a year. Why? Because decaying organic matters, dusts, molds, viruses, & other contaminants can get trapped in them & are harmful when they've propagated in excessive quantities. 2x a year when I take the cabin filter out, I usually see dried leaves & even dead bugs getting trapped in it considering I only take my car out on weekends. What more if it's DD?. Imagine the kinds of bacteria that these carry & can get blown to into the cabin. Worst if you live in a humid place &/or use the AC often which is a suitable condition for mold cultivation.

Same thing with intake air filters, they can get clogged with debris, esp. dusts & bugs, depending on the area where you usually drive on. It's advisable to inspect, clean, and/or replace them often esp. if you're in a dusty area like the beach, dessert, unpaved roads, or environments with lots of bugs, etc. Aside from the contaminants getting trapped, perhaps another factor is the structural integrity of the paper's weaves too as they can get damaged from particles hitting them & the air pressures going through them.

For both, I've invested in washable air filters since I clean them once a year (perhaps I would have stayed with paper for the intake since they are already very efficient stock but my FRS already came with aftermarket).

Other items are time sensitive especially rubber components like door seals, tires, bushings, & even the shock absorbers. Tires are recommended to be changed after 6-8 years as they have a shelf life of 10 years as the oil in the rubber dries up & the material gets brittle even if the tire was never used & kept in storage. Shock absorbers/struts typically have 8 years shelf life even if the car's not used often or just sitting in the garage (premium ones like Bilsteins last longer).

[Bonburner]

Originally Posted by thomasmryan

oil will absorb moisture so i would drive it 30-40 minutes once a month to cook that off.

What?
Oil is hydrophobic, not hygroscopic.

[Grady]

Originally Posted by Bonburner

What?
Oil is hydrophobic, not hygroscopic.

Yes, but moisture will build up inside the engine with ambient heat cycles. It will not mix with the oil but will be in the oil pan separate from the oil and on hard parts in the engine. Getting an engine to temperature for extended periods of time or changing the oil is the only way to get it out. This is why a time limit is listed. Location has an effect also, Florida would be a lot worse than Arizona. If you are in Florida type environment I would stick to the manufactures recommendation. AZ you can probably go 2 years with less buildup than 6 months in FL.

[Dadhawk]

Originally Posted by Grady

Yes, but moisture will build up inside the engine with ambient heat cycles. .

You are also likely to get condensation, and thus water, in your fuel tank if it sits for long periods of time and not full. Happens more with metal fuel tanks but I imagine non-metal ones could do the same.

[Dadhawk]

Originally Posted by sygfrid

For more experienced motorists, we do them when deemed necessary (more frequently &/or earlier than what the sched says).

Once out of warranty, I'm in this camp. The only thing I change on a regular schedule is the oil. Everything else is based on inspection and performance.

[Tcoat]

Originally Posted by Dadhawk

You are also likely to get condensation, and thus water, in your fuel tank if it sits for long periods of time and not full. Happens more with metal fuel tanks but I imagine non-metal ones could do the same.

Very, very, very little moisture will accumulate in a modern sealed fuel system. It is so little when the system is active that it is almost unmeasurable. There is zero when it is just sitting as there is no air exchange.