This seems to be in mind a lot lately, mainly because with my 8 hour oil change intervals and two oil filters to change each time; the cost is racking up. But who wants to gamble with your own engine experimenting with ways to save some cash? I don’t like the idea of a limbo dance with ever cheaper oil and filters, how low can you go… before you have to replace the top end?

 

Maybe there are other ways of testing an oil filter beside using your own engine as the exotic £1000+ sacrificial budgerigar – “Is it dead yet? OK then, try again.”

Well yes, you can look at the oil after it has done some service in the engine, and there are a lot of tests you can do to the old oil, look at the viscosity, the colour, separate the impurities, look at it under a microscope and measure the side and shape of the particles suspended in it, test for conductivity and PH, use a magnet to try and test for steel fragments and so on. But which of these tests is worth doing? First you have to decide what it is that the oil filter does, well fundamentally oil filters physically remove solid particles above a certain size – like a net with certain size holes will catch fish bigger than the holes and let all the smaller ones though, they keep a certain oil pressure as they restrict the flow of the clean oils though the motor – this is basically related to how restrictive they are (how small the holes) and how much filter paper is used (if more of it is folder into the filter the oil has more holes to pass though and the easier the flow), this changes as they get more and more blocked with use. To some extent the paper ones are hydroscopic and help take some of the water that may have got into the oil, this is because cellulose paper will soak up a little water and hold it.

These days manufactures are under pressure to make the oil change intervals as long as possible, this means the filters need to be big so as not to block up and stop the oil flow, especially as the oil gets older and dirty, the other way to make the oil filters last longer is to make them less filtering, i.e. if they have larger holes they will be much harder to block, but that means that the bigger holes will let many more particles though and ones that are more likely to do damage…one thing that helps is that as the oil gets older it gets thiner or less viscus, this helps a little as the thinner oil passes through the filter easier, this counter acts the blocking of the filter over time to some extent.

 

Still, what to do?

Original filters-best oil-leave it in a little longer?

Cheaper oil-good filter-change often?

Stainless filters-buy once-remove wash and replace?

Budget filters-budget oil-change oil under specified hours?

not an easy one, especially if money is important…