# MD2030 Which Volvo Filter? 3581621 or 3840525



## Peas (Oct 11, 2011)

I have seen on volvo parts lists, that the proper filter is 3840525.
The filter that was on my boat when I bought it (second hand) is 3581621.
I've also seen on web searches that 3581621 is the proper filter.

The gasket size seems similar (although not exact) but the biggest difference is 3581621 is about twice as long as 3840525 is.

Which one do I use??


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## Classic30 (Aug 29, 2007)

Peas, welcome to Sailnet. An introduction would be nice. 

To answer your question: As you say, the proper oil filter for your engine is the Volvo 3840525. That is the one you should be using.

The other one is probably an aftermarket replacement for the original. An oil filter is hardly a sophisticated piece of kit, but, if it's time to replace it, I'd think you'd be crazy to use anything but the correct unit. Volvo engines are temperamental enough already..


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## Peas (Oct 11, 2011)

Thanks for the quick reply.
I went back to the local Penta service centre and they advised that the 3840525 was the original spec and the 3581621 is the new spec, which is a larger capacity filter. Not sure if that is the case, of if it was just what he thought would be a reasonable response as to why my engine had a Volvo 3581621 filter on it.

In any case, I have an engine with fresh oil now and a 1 year old filter. I used the motor for maybe 40 hours...what are thoughts on if that filter will hold for another season, or if I should do another oil change in the spring, when we relaunch our boats?


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## Classic30 (Aug 29, 2007)

Peas, that could be true, but since (a) best practice, and the Operating Manual, say to replace the filter when you replace your oil and (b) most sailboat people don't run their engines for anywhere near the 100hour factory-spec interval between changes, having a bigger filter is a waste of money. IMO.

If you have the bigger filter already, I suggest you change both in the spring - for the correct one this time.


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## airtime (Jun 16, 2002)

I'm not sure when the engineers re-spec'd but the MD2030 I installed new about 10 years ago came with the 3581621. 3581621 is a Volvo part number - not aftermarket so it is the correct filter for the engine now. 

I agree with Heartly18 and change the filter annually. I do the filter change at the start of the season with new oil and an oil only change prior to haulout. On the rare seasons where I do get 100 hours on the engine, I do filter and oil at that time in addition to the launch / haulout changes.

Fair Winds

Al


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## subpack (Sep 23, 2007)

Part numbers for oil and fuel filters MD2030.
Oil filter is 3581621
fuel filter is 3840525
cross reference for fuel filter is Wix 33386


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## subpack (Sep 23, 2007)

I will post cross reference for oil filter when I get it.
Ken


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## subpack (Sep 23, 2007)

Hi.
Filterfor oil is 3581621 and fuel is 3840525
You can get cross reference here.
VOLVO FUEL AND OIL FILTER CROSS REFERENCE - Cruisers & Sailing Forums
Hope that helps.
Oil filter should be changed at least once a year and fuel filter as well. if engine makes black smoke, it is sometimes because of blockage of fuel filter.
Ken J-mech (Diesel Mech)


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## vtsailguy (Aug 4, 2010)

subpack said:


> Hi.
> Filterfor oil is 3581621 and fuel is 3840525


Is that the right way around?


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## Desmodromic (Nov 6, 2016)

Unlike many I believe in continuing old threads if there's something to add as lots of us use forums for research/information.......
3581621 and 3840525 are BOTH VOLVO OIL filters. I have them both in front of me and have used both successfully (a season at a time) on my D2-55B (so that's a 2004, non-turbo'd 4 cyl 2+litre engine which does about 50hours a year). The reason I specify size, 'non-turbo' and hours is because that means it's overall a fairly unstressed, cool-running unit which will not be too fussy about oil type or filter efficiency. A turbo'd engine generates more heat/stress on components. However at 10.5 litres capacity it is as much an oil-cooled engine as a water-cooled one (no helping blast of air explains why most marine engines have higher oil capacities than car engines....)

Limiting the discussion to screw-on canister filters the _major_ differences (apart from physical considerations such as seal dia (which IS the same on these two), screw and space issues) are the filtration media used (cleaning ability) and the capacity (flow oil fast enough and not clog up with particles quickly). Which also means, if the physical connection fits/seals, then in an emergency any filter is _usable_.....
- So the media inside differs to meet usage conditions - harsh or normal; tropical, temperate or cold (climate & oil viscosity affect filter flow) - and relates to particle sizes and oil flow 
- The filter capacity is VERY loosely related to the engine's oil capacity (more or less oil to clean, therefore particles to hold without reducing flow). But a coarser media will require less physical space to flow enough oil. Is this then the difference between 3581621 and 3840525?
One manufacturer of vehicle filters, MANN, uses a great product numbering system to show variants of the same filter (eg WK854/3 and WK854/5) which tells you what kind of media is being used. Whenever I have the choice I opt for the 3581621 as its bigger capacity _seems_ more suited to the engine's large oil capacity (more oil to be flowed/filtered), but I don't worry if I have to fit 3840525. 
I would really like to hear a Volvo R&D engineer's explanation of the two!


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## RichH (Jul 10, 2000)

Filters used for oil lubrication of internal combustion engines are essentially all 'recirculation mode' filters ... the oil gets filtered (@ approximately upwards of 15 US gallons per minute or at about about a max. of 50 lpm) .... over and over and over and over again. 
Such filters, all, are rated (for single pass flow) between 16-18 µM at a retention / capture efficiency between ~90 to 97% (weight). 
The filter media (a blend of long strand modified cellulose and glass micro fibers plus some 'resin') used in such filters is usually from a single (monopoly) world source - Ahlstrom of Helsinki Finland (or one of its worldwide manufacturing centers). Ahlstrom makes the 'paper', the filter manufacturers make the componentry that hold the technical paper together. The 'cheap' suppliers of such filters typically use 'broke' cellulose - scrap cellulose that was used to make other technical paper; the 'broke' was what was cut off and re-processed (short fibers)

For recirculation mode operation that 16-18µM 'rating' is essentially meaningless, as such for each 'pass' of the 'turnover' of lube oil there is a statistical reduction of particles that do pass (some larger than the 'static' rating of 16-18µM) but by statistics will be removed on the next or later, etc. pass through the filter. This statistical reduction with recirculation filters has been known and accepted for automotive recirculating lube oil filters since the late 1930s to mid 1940s. Such 'recirculation' mode will quickly (by statistical reduction) lower the 'effective' recirculation mode capture value to ~1/5 of the 'single pass µM value', or in the case of automotive oil filters: somewhere in the range of ~4µM (as a target size). All such filters have a % of capture sites at lower/smaller µM values than the static/single pass µM rating. Do websearch for "filter" + "Beta Ratio". 
Recirculation filtration is entirely based on 'throughput' flow rate, effective filter area (sq. ft. / cm squared). The larger the surface area, the less resistance; hence, the 'faster' and 'more' the flow; hence the statistical reduction to the 'target' µM at a faster rate. 
BTW - if for some unknown reason, you want to effect this filtration in a 'single pass', then you'll need a ~4µM filter .... at 5 times the surface area, a MUCH stronger pump, and a total increase of about 6-7 times the cost.

Simple speak: use the LARGEST (internal surface area) lube oil filter that will fit.
'Brands' from ethical** filter manufacturers simply doesn't matter. 
In an emergency, for '_recirculation_' filtration one could use compressed pubic hair, feminine hygiene pads or even toilet paper; however, the statistical reduction of the _numbers_ of particles to the 'target' µM level would take longer due to flow resistance issues. Want a 'tighter' µM reduction; then, speed up the flow rate.

** most 'ethicals' use an Ahlstrom or equivalent _technical_ paper for the filter media.


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## albrazzi (Oct 15, 2014)

Never have never will do an oil change without a filter change, I just cant see why.


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## basta (Jul 3, 2021)

Airtime mentioned doing an oil change at the beginning of the season, but I would argue that leaving that task till the start of a new season leaves old oil sitting in the engine for months and may not be best practice. Why not change it at the end of the season, you will still have fresh oil at the start of the season, but not the potentially acidic residues wintering over in the engine. S/V Akari Blaine WA.


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