Oil Filter Codes: What Do They Mean?

Hi!

Standing in the aisle at the hardware store, I was bewildered by the variety of Mahle oil filters and was examining all the VW filters. From a threading and flange perspective, they are practically all the same, but they differ in length and diameter.

'For my car, relatively thick filters, ranging from short to long, are suitable. The original equipment filter was a long Bosch filter, but ATU always provided me with a shorter filter based on the part number.'

I just bought the long 'OC51' filter because it wasn't much more expensive than the shorter ones, and I think it can hold more dirt.

Now, let's get to the question:

1.) Why are there different types of Mahle filters that look identical on the outside, but have different prices? Is it due to different quality levels?

2.) What does the 5-digit code printed on the filters mean? For the OC51, it's 03 W 37. It almost sounds like engine oil specifications. Does it indicate the micron rating?

I have not observed any correlation between the code and the price.

I couldn't find any specifications for oil filters in my Seat owner's manual.

3.) How should I proceed with filter selection when a large number of filters of different types and shapes fit into my car, and the operating manual doesn't provide any information?

Sure, here's the translation:

'Thank you in advance.'

http://www.cheesebuerger.de/smilies/schilder/61.gif

Unfortunately, I couldn't find any information on Google or on the www.mahle.com website.

It's a shame that I didn't receive as detailed answers to my question about oil filters as I did to my several parallel questions about the type of oil.

Does anyone know anything about the qualities and specifications of oil filters, and the regulations set by vehicle manufacturers?

If anyone has any information about oil filters (experiences, anecdotes, links), please feel free to share it.

On http://www.mann-hummel.com/mannfilter/upload/doc/HBEKA_4ayFC.pdf, I at least learned that there are filters with an overpressure valve, which bypasses the filter path during cold starts (when the oil is difficult to filter) or with a used filter. Do all oil filters have this valve?

Sure, here's the translation:

'Thank you in advance.'

I think I can at least help a little bit.
To my knowledge, all filters have this valve. You can also see the spring through the connector.
I've heard from an expert that a filter problem caused numerous engine failures. (It had something to do with the valve.) Unfortunately, I don't know the manufacturer. But according to the expert, this wouldn't have happened with a Mahle filter.
The valve opens when a certain back pressure is reached in the filter. However, I can't imagine how that would work during startup.