What this filter does and which engines it fits

The Mercury Marine Mercruiser oil filter part number 35-866340K01 is a spin-on filter designed for inboard and sterndrive Mercruiser engines. A 2-pack means you're getting two filters, which is useful if you change your oil twice a season or maintain multiple boats with the same engine type. This filter removes dirt, metal particles, and sludge from your engine oil to keep the engine running cleanly.

Before you buy, confirm this is the right filter for your specific engine. Mercruiser makes engines in different sizes and configurations — inboards, sterndrives, and jet drives — and not all use the same filter. Check your owner's manual or the filter cross-reference chart from Mercury Marine to match your engine model to this part number. Using the wrong filter can mean poor oil flow or a filter that doesn't seal properly.

Key Takeaways

  • The 35-866340K01 is a spin-on filter for certain Mercruiser inboard and sterndrive engines, and you should verify it matches your specific engine model before purchasing.
  • A 2-pack is economical if you change oil twice yearly or own multiple boats with the same engine type.
  • Spin-on filters screw onto a threaded port on the engine block and are faster to replace than cartridge-style filters.
  • Changing your oil filter every time you change oil — typically once or twice a season for recreational boats — keeps your engine protected from wear.

How to identify if this is your filter

The easiest way to confirm you need this filter is to look at the filter already on your engine. If it's a spin-on (cylindrical, with a threaded base), note the part number printed on the side. Compare that number to 35-866340K01. If they match, this 2-pack will work for you.

If you can't read the old filter or don't have your manual handy, contact a Mercury Marine dealer with your engine's model and serial number. They can tell you the correct filter in seconds. Buying the wrong filter wastes money and risks engine damage, so this step is worth the phone call.

Spin-on versus cartridge filters

Mercury Mercruiser engines use one of two filter styles: spin-on or cartridge. The 35-866340K01 is a spin-on, meaning it screws directly onto a threaded port on the engine block. When you change it, you unscrew the old filter, wipe the port clean, and screw on a new one. The whole job takes a few minutes.

Cartridge filters, by contrast, sit inside a housing on top of the engine. You unscrew the housing cap, pull out the old cartridge, and drop in a new one. If your engine has a cartridge filter, this spin-on won't fit. The two styles are not interchangeable, so double-check your engine before ordering.

What's included and storage

A 2-pack of the 35-866340K01 gives you two complete filters. Each one comes with a rubber gasket already attached to the threaded base. You do not need to buy gaskets separately. Store the filters in a dry place — a garage shelf or boat locker works fine. Filters don't expire, so you can keep the second one until you need it next season.

Keep the filters away from extreme heat or moisture. A sealed box or bag is ideal. If a filter gets wet or dusty before installation, wipe it clean with a dry cloth before screwing it on.

When to replace your filter

Change your oil filter every time you change your engine oil. For recreational boats, that's usually once or twice a year, depending on how often you run the engine. If you use your boat heavily — fishing trips, water sports, or regular cruising — change the filter at the start of the season and again halfway through. For light use, once a year is often enough.

Some boaters change the filter every 50 to 100 hours of engine run time. Check your owner's manual for the manufacturer's recommendation for your specific engine. Saltwater use may require more frequent changes because salt and moisture break down oil faster than freshwater.

Cost and where to buy

The 35-866340K01 2-pack is typically priced between $30 and $50, depending on the retailer. You can find it through Mercury Marine dealers, online marine parts suppliers, and some general automotive retailers that stock marine filters. Prices vary, so compare a few sources before ordering.

Buying a 2-pack is usually cheaper per filter than buying single filters separately. If you only need one filter right now, you can still buy the 2-pack and store the second one for next season — it will cost less overall than buying singles twice.

Frequently Asked Questions

Can I use a different brand filter on my Mercruiser engine?

Yes, many aftermarket filters fit Mercruiser engines and meet the same performance standards. However, confirm the part number matches your engine type. Using a filter designed for a different engine can cause poor oil flow or leaks. Stick with Mercury Marine filters or verified cross-reference alternatives from reputable marine suppliers.

How tight should I screw the filter on?

Screw the filter on by hand until the rubber gasket touches the engine block, then turn it another three-quarter turn. Do not use a wrench — hand-tight is correct. Over-tightening can damage the gasket and make the filter hard to remove next time. Under-tightening can cause leaks.

What do I do with the old filter?

Old oil filters contain used oil and should be recycled, not thrown in the trash. Many auto parts stores and marine dealers accept used filters for free. Some recycling centers also take them. Drain the old filter into a container before dropping it off to prevent spills.

Will a 2-pack last me a whole season?

That depends on how often you change your oil. If you change oil twice a year, a 2-pack covers you for one full year. If you change more frequently or run the engine heavily, you may need more than two filters per season. Check your manual for the recommended change interval for your engine.