We've been asked about aftermarket filter caps a few times before, and we really didn't have a good answer because it's just not something we've researched. After all we make tools not parts, right?  

Earlier this week we had a customer contact us because he was having an issue with our MX2341 oil filter drain tool. He was trying to use it with his newly purchased aftermarket aluminum oil filter cap.

Here's an excerpt from his actual email:

"When I threaded the fitting into the bottom of the oil cap it will only go halfway and it knarled the threads on the fitting and in the end of the oil cap. Is this a common issue and do you have a remedy for this?"

While we've never had this type of issue before with one of our drain tools, we needed to investigate. Of course, it's possible that there was some issue with the newly purchased oil filter cap as well, right?

So, that same day we ordered up a brand new aftermarket aluminum oil filter cap (it's a popular brand but we're not naming names), and a brand new factory Toyota aluminum oil filter cap.  

When these arrived we closely inspected both, and the difference was absolutely shocking.

Filter caps appear similar at first glance.

That's a side-by-side photo of both aluminum caps. They look about the same, right?

At first glance it would seem that the aftermarket replacement would be a reasonable choice, especially at a savings of a few dollars.

Casting line has been ground off on the aftermarket cap (left).

The first thing that really stood out was the grinding marks where the casting line (flashing) has been removed on the aftermarket cap. It appears that the line was quite heavy initially and grinding was required.  

We noted that some Amazon reviewers complained that there were metal shavings inside the cap when they received it, this is possibly the cause.  

Note the OEM Toyota cap on the right has a nice neat casting line that doesn't require grinding.

Ok, here's where things get ugly.

We removed the drain plug from the bottom of the aftermarket cap, expecting to see clean threads. Instead there was this (see photo on the left). The threads are the same pitch as the factory cap, however they were completely trashed.

Drain plug threads on aftermarket cap are trashed (left)

Despite the severly damaged threads, we were able to install our drain tool into the aftermarket cap.

Note: We also threaded the aftermarket drain plug into the new Toyota cap and upon removal it severely galled the threads - essentially destroying it. Good thing we took photos before trying this!

We have one of those USB microscopes that we use from time to time for quality control and testing, we decided to break it out here to have a closer look at the threads.  

The photo above is of the OEM Toyota oil filter drain plug threads. They're beautiful.

The photo below is of the aftermarket cap. Not so much.

We disassembled the tube, spring, and valve assembly to have a look inside. More bad news for the aftermarket part.

The drain valve differs significantly from the factory part.  

It looks like the point on the aftermarket valve (left) has been flattened. It's unknown if this is intentional or not but is somewhat concerning. Our drain tool was tested with this valve and still functions properly.

Point on aftermarket drain valve has been flattened (left)

We also inspected the tube because it felt light compared to the factory part.

Sure enough, it was made using 20% thinner metal. The factory tube (right) thickness measured .010" and the aftermarket was .008".

Tube metal thickness is 20% thinner on aftermarket cap (left)

There you have it, a side by side comparison of an aftermarket and factory aluminum oil filter cap for Toyota engines from our perspective.

In looking over some of the Amazon reviews, some people don't appear to have any problems with the aftermarket cap while others do.

Maybe they had a bad production run, or a quality control issue? After all things like that do happen from time to time.

Based on what we've seen with the two caps we received, pony up the extra few dollars and get the factory part.  

We hope you found this information useful. If you have any questions, think we missed something, or need anything, just let us know!