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Oil Filters - What's the Best One?When it comes to oil filers you have a lot of choices.
A while back we asked ourselves - "What filter is best filter for our Miatas?"We decided to check out some of the filters the old fashion way - by cutting them open.Here is what we found.In the group, the Mazda filer was the smallest - so we figured that is would have the least amount of surface filtering area. Boy were we wrong.The Mazda filer had almost three times the amount of filtering area as compared to the biggest filter - the FRAM.The Mazda filter had about twice as much as the Purolator and the AC Delco.At the time the Mazda and the FRAM were the only two to have check valves (none of the others available now - including the Fram - have check valves of any sort).So - who needs a check valve anyway? Well what the check valve does it force the filter to work as a filter. It also keeps the filter from back flushing which can happen with any sudden drop in oil pressure. The others, if they get a little clogged, or with a sudden drop in oil pressure, the filter stops filtering and is bypassed. The check valve in the Mazda filter prevents this from happening.So - if you are out looking for a better filter - it probably hasn't been made yet. Someone would have to work pretty had to make a better filter then the Mazda filter - and they would have to make a hell of a lot of them to even come close to the price Mazda sells theirs for.So instead of worry about filters - go for a drive.NEW INFO(Postscript - around late 1999 Mazda changed their filters. Last time we bought any Mazda oil filter we bought a couple of case and haven't bought any new ones yet. But here is a report from (Beau) Beauchamp Ken and Michele, many thanks for your replies to my questions about oil filters and pressure. Taking your advice, I bought a Miata filter at the local dealer here in Virginia Beach. I too was pleasantly surprised at the price, but, I see that the filters no longer have a check valve at the outlet, rather, they have an anti-drainback, silicon rubber, flapper valve covering the inlet ports. Several brands of after-market filters have this feature also. As for access to the filter from above, I could get the somewhat arthritic fingers of one hand on the filter, but could not get a tool on it to loosen it. So, I removed the belly pan, loosened the filter from below, and removed it from above. This is the hardest filter to change I have ever seen. I also was able to access the oil pressure sensor from below and changed it out at the same time (for info, after-market sensors cost 65% less than Mazda sensors), oil pressure is now much improved, 25 psi warm idle and 50 psi at 3000 rpm. Although the cold variable resistance values of both the old and new sensors was virtually identical, I suspect resistance of the old sensor was increasing with heat as the sensor aged. I only have the one Miata, but have a 89 626 and a 91 B2600i so I might just go back to using Mazda filters as soon as I exhaust my supply of Fram and Penske filters. Again, sincere thanks for your prompt replies and good advice. Jim(Beau) Beauchamp
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