Mazda oil filters: 1WPE-14-302 vs. 1WPY-14-302

These filters look and fit the same. Is there really a difference between these two filters? If so, what is it?

We’re going to cut two brand new filters open on our lathe and find out.

In the past Mazda has issued service bulletins stating that even though they make some oil filters that are apparently identical on the outside, the inside of the filters are different and using the wrong one will cause engine damage.

While no such TSB exists for these two filters, we’ve been using the 1WPY-14-302 on the 2021 Mazda vehicles that call for it. They’re the same price, so there’s no reason not to use the right filter. Still, you’ve got to wonder what the hell Mazda was thinking when they made two filters that look and fit identically with nearly identical part numbers. It’s really easy to grab the wrong box.

As you can see, the boxes are pretty easy to mix up. We’ve had our dealer deliver a case of one when we ordered the other, and we’ve had to remove filters and throw them in the trash after installing the incorrect one.

Mazda oil filter chewed up on a lathe
Sometimes I don’t plan things out so well.
Eventually it worked out without harming any more oil filters.

The most obvious way they could be different is the filter element. There is a difference, but it’s very small. The 1WPY has 44 folds, which are 16mm deep and both are 50mm high. The 1WPE has 43 folds but the dimensions are the same otherwise

I cut a chunk of the filter paper out so I could measure a single layer. The thickness of the filter media is 0.72mm thick on both Mazda oil filters.

I also checked the filter paper under a microscope. As far as I can tell it’s the same stuff.

Is there a difference in the mounting flange? Not that I could find. The thread size and pitch is identical. There are 8 holes in each and the holes measure 4mm x 10.3mm on both.

It’s notable that there’s no anti-drainback valve, which seems kind of cheap, but maybe all of the vehicles have something built in for that. I didn’t do any research on this. The fact they’re identical is good enough for today’s project.

So is the center support different? Nope. Each has seventy eight 2.85mm holes

It’s possible that the by-pass valve is different. The valve and opening are the same size, but the spring may be a different rate

After a bit of thought I decided to test it like a valve spring. I don’t have a valve spring tester (and this spring would probably be too light and out of its range anyway), but I do have a scale and a dial indicator.

I set the valves on the scale to measure one at a time. While pushing the valve open I used the indicator to measure 1mm of movement, then checked the scale’s reading. If the springs are the same, the reading should be the same. The 1WPY’s spring is 3300 grams @ 1mm of compression. The 1WPE’s spring is 2200 grams @ 1mm of compression. This is a pretty big difference.

So what is a by-pass valve? A by-pass valve is a safety measure. If motor oil can’t flow through the oil filter, the pressure will increase behind the valve and will push the spring open so the engine doesn’t run dry.

Why wouldn’t oil flow through the filter? The usual reason is lack of maintenance. The oil filter captures debris and eventually the debris clogs the filter and oil can no longer flow through it.

Another reason the by-pass valve might open early is that motor oil can be thick when the weather is cold and the car is first started. The thick oil is slow to push through the filter paper so pressure builds and the valve opens.

Why would the older Mazda cars use a lower pressure by-pass valve? I don’t really know, but I’m going to take a guess.

Typically, older cars use thicker oil and more modern cars use thinner oil. Modern cars also use synthetic oil which allows for better flow when then weather and engine are cold. Thicker oil will have a harder time flowing through the oil filter when cold. One often stated reason for the use of an oil by-pass valve is that it allows oil flow on cold starts when the oil is very thick.

So here’s my theory (which is quite possibly wrong). Maybe Mazda is more worried about keeping debris out of the oil than oil flow on cold start, since the motor oil is now very thin synthetic. To make sure no unfiltered oil is delivered, they increased the by-pass valve blow-off pressure so the valve only opens when the filter is truly clogged; they’re no longer worried about cold start up.

Ok Cunningham’s Law, work your magic.