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I have a car on which the filter is fiendishly difficult to access (Alfa GT 3.2) and as I want to keep the car running for many years (and drive it quite hard) I want to supplement the manufacturer's recommended service interval (12K miles) with an additional oil change.

Given that changing the oil itself is fairly simple but the filter is very complex, I'm considering only changing the former (between services) but I want to know if there's actually any point in this if the filter isn't changed.

Just to avoid any confusion, the question here is:

Either change oil and filter at 12,000 miles

Or change oil and filter at 12,000 miles and change oil at 6,000 miles.

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    Honda did this for years before moving to full synthetic, their filters (honeywell) were rated for 10k miles but they were using synthetic blend and recommending changing it at 5k. So at 5k you just got an oil change, and at 10k you got an oil and filter change. That's probably the largest experiment you could ever ask for. – finleyarcher Mar 13 '18 at 0:23
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Either change oil and filter at 12,000 miles

Or change oil and filter at 12,000 miles and change oil at 6,000 miles.

I too have a car with a hard-to-reach oil filter and routinely go for the latter, changing filter very 24k km and oil every 12k km.

Rationale: in almost all cars oil pump is volumetric, gear type. This means that the amount of oil reaching engine internals is NOT influenced by how dirty the filter is. Only the "effort" made by the pump to push oil thru it changes (and a bypass valve saves engine and pump in case of excess pressure) so you know that your engine will be having the oil flow it need. Moreover, in a perfectly working engine the amount of dirt "caught or trapped" by the filter is very low anyway and little influenced by the driving style. So no big deal in running it for the "full term" specified by manufacturer.

Oil, on the other hand, really gets "trashed" by older engines and sport driving (higher piston blowby) so there is a clear advantage in changing it more often. If you want to go "full science" on it you can install a differential pressure sensor across your filter and send you oil to a lab every ~3k km and find out what its wear pattern is.

Personal experience: after 12k km of hard driving the oil from my W10 engine smells like gasoline and has lost (empirically tested) viscosity in a noticeable way. After 16k km the wear is so bad that after replacing it the engine sounds different (not unexpected on that engine).

  • Why don't you try replacing the filter with a dummy and see what happens to the wear? Filters do an important job and are effective... – Solar Mike Mar 12 '18 at 12:31
  • I am aware of how important the oil filter is, stil especially on an older engine like the "beating" on the oil is noticeably higher that new, so a lower change interval is a good thing. The dirt that the filter has to catch is around the same as new or less so no big deal in running the filter for the manufacture specified life and the oil for half of it. Honda by the way says change filter every other oil change. Anyway, a filter is so cheap that there are no big reasons not to change it every time oil is changed... – Caterpillaraoz Mar 12 '18 at 13:08
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    This was your statement and why I commented : "Moreover, in a perfectly working engine the amount of dirt "caught or trapped" by the filter is very low anyway..." – Solar Mike Mar 12 '18 at 13:13
  • Yes I could have expressed my idea in a clearer way. What I mean is that the dirt being filtered it very damaging to the engine, thus the fundamental importance of the filter, but the the amount of that dirt that the filter can stop before starting to "clog" is rather high. Or better said, a filter gets clogged at a slower pace than the oil degrades. – Caterpillaraoz Mar 12 '18 at 14:18
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If you plan on changing the filter at the recommended interval and changing the oil more frequently that will be fine.

Perhaps, if changing the filter is that difficult, it would be worth getting it changed by a shop...

I went the opposite route when I was using Mobil 1 5W:50 oil : I changed the filter twice as often and doubled the mileage on the oil.

  • To be clear, I'm not planning on doubling the service life of the filter - it's getting changed at 12K miles whatever I decide. This is about whether or not to bother changing the oil at 6K miles without also changing the filter. – Matt Bowyer Mar 11 '18 at 18:46
  • If the filter is changed at the standard interval it should be fine, and if you are planning on changing the oil early then that's fine. I'll have to edit my answer... – Solar Mike Mar 11 '18 at 18:48
  • The question isn't so much whether it's fine (as I can work out that it would be) - it's whether it's actually helpful! – Matt Bowyer Mar 11 '18 at 19:02
  • So, for any non-opinion based answer then you should send your used oil after it has been used for the full service interval for chemical analysis and then send a sample of oil that has only been used for half the service interval... But, logic would say yes as it is carrying less pollutants etc, but is that reduction worth the cost ? – Solar Mike Mar 11 '18 at 19:05
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    @MattBowyer As Fred has said and I said : send two oil samples for testing, one from the full service interval and one from half... which is the only way to be sure. – Solar Mike Mar 11 '18 at 19:13
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This isn't a direct answer, but I'm certain somebody makes a "remote" oil filter arrangement to relocate the actual filter element. This really isn't anything more than a filter substitute housing, with some Aeroquip braided lines to bring it somewhere more convenient.

This would also allow you to use an advanced filter like an Oberg unit with a washable 60 micron screen. Although this requires more maintenance, it's a simple (albeit dirty) process and would protect your engine far better than any pleated paper product. And the expense is somewhat mitigated in that it's the last filter you'll ever buy.

Just a thought.

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Having an Alfa Romeo myself I suggest that you change the filter every 6,000 km along with the oil. If you want to drive it hard and keep it on the road a long time, you start to service it right. This is only if you "cruise" it and change gears at 4-5,000 RPM / Gear.

If you drive it in the city (2-3rd gear mostly) then you can change the oil and filter once / year (12-15,000 km). I also recommend changing the other filters too every year (fuel, air, pollen).

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