Changing fuel filters on the Universal M25 diesel

December 15, 2011
Update October, 2012

The first time I wrote this up I was draining the Racor fuel separator bowl before removing it. No longer going through that mess! Here's the new tips, thanks to Gary Kowal, Horizon Marine - a real pro who happily shared his tips, tricks and techniques!

  • Use hose pinch pliers to pinch off the fuel line instead of turning off at the fuel tank
  • Take the Racor R24T off without draining the bowl. Sure, there's going to be fuel spilling - keep those absorbent towels handy!
  • Grease the R24T gasket with Super Lube Synthetic Grease before screwing the bowl back on.
  • Hand tight the bowl on the R24T filter? Forget it! it will leak, use some leverage to get that bowl on there tight, using a screwdriver between the bottom knobs does the job nicely.
  • Don't even try to start the engine before bleeding the air by using the air bleed plug on the engine fuel filter.

Parts & Supplies

Super Lube Synthetic Grease
Super Lube Synthetic Grease
Quart size container
Quart size container
  • Racor R24T Fuel filter - $37.99, West Marine
  • AC Delco TP1200 Fuel Filter - $19.00 Quivera Marine Service Center
    • or WIX 33390 - O'Reilly Auto Parts $12.38
    • or Napa #3390
    • or Universal Part #298854
  • paper towels, shop towels, and absorb sheets
  • Quart size plastic container or 1 pound coffee can for the contaminated fuel out of the Racor
  • Waste receptacle for the old fuel filters
  • A container of clean diesel fuel
  • Super Lube Synthetic Grease - to lube the gasket on the Racor
  • Spray Nine Marine Cleaner - to clean up the fuel spills


  • FRAM Adjustable Oil Filter Band Wrench - (swivel handle), WalMart
  • Screwdriver
  • Optional: Hose pinch pliers - to pinch off fuel line instead of turning off at the tank

Shut off fuel at the tank
Shut off the fuel supply at the tank

How to change the Racor R24T primary fuel filter

Shut off fuel supply

  1. Turn the valve at the fuel tank to shut off the diesel fuel supply.
  2. Put paper towels or rags or something absorbent under the filter and the area you'll be working in, there will be fuel spilling.

loosen vent plug
Loosen the small white vent plug on top of the Racor unit. It's the one near the arrow on top.

Update - No need to drain the Racor R24T separator bowl

Just skip over this section and be happy you don't have to mess around with this!

  • Use the screwdriver to open the vent screw on top of the Racor fuel filter/water separator unit. Just open it. Don't take it off.
    • The vent plug is the small screwable plug on top, not the large screwable plug that is to the right of the large knob.
drain the gunk
Small bottom screw out. You need a bigger container than this cup!
  • Get ready with your container. The large red plastic cup shown in the photo is NOT quite big enough.
  • What plug is the drain plug?
    • Good question, tried undoing the knob first and nothing came out
    • Called Racor tech support to find out which plug on the bottom was supposed to be the drain. He said the small one you take off with a screwdriver. Hmmm, I don't think so - you would think the knob you can unscrew with your fingers would be the drain plug for this common task. Oh well, it wasn't draining out of the big one so...
  • Use the screwdriver to unscrew the drain plug from the bottom of the separator bowl and drain it. Don't lose the plug!

loosen filter clockwise
Loosen the filter clockwise

Remove Racor filter assembly

  1. Get ready with your empty container and a waste receptacle for the filter. You can try to position it under the filter to help prevent spills. That doesn't work on Reality Check because the sea pump hose to Heat exchanger is pretty much in the way.
  2. Unscrew the filter (clockwise)
    • If you can't get the filter off the unit by hand, use the adjustable swivel band wrench to loosen it and then take it off.
  3. Dump the fuel from the filter into the container.
clean bowl
Clean out the separator bowl with fresh diesel on a paper towel.
If you need a replacement bowl, the P/N is RK 20135. It's discontinued but they're still around.
  1. Remove the water separator bowl from the filter and discard the filter.
    • If you can't get the bowl off the filter by hand, use the band wrench to loosen and then take it off.
  2. Clean out the bowl with some clean diesel on a paper towel. IF you removed the plugs (no need to do this because you didn't mess around draining the bowl, right?), screw them back in the bowl.

Before you put the primary Racor R24T filter back on, change the fuel filter that's on the engine

If you're going to change the secondary fuel filter, do it before you put the Racor back on. Jump down to "How to change the secondary fuel filter". It's just easier to change the one on the engine without the Racor R24T filter assembly in the way.

Screw filter back on unit
With the filter and bowl FULL of clean fuel, screw back on the unit by hand

Install the new Racor R24T filter

  1. Open your new Racor R24T and the package of new O-rings that came with it.
  2. Use the Super Lube Synthetic Grease all around on both of the new O-rings and put them on.
  3. Screw the separator bowl onto the new filter. Hand tight is NOT good enough, you need some leverage to get it on tight enough so it won't leak.
    • The fuel separator bowl has 2 knobs on the bottom - lay a screwdriver blade between these to get some leverage and use the screwdriver as a handle to tighten the bowl.
  4. With new filter-and-bowl held over an empty receptacle for clean fuel, fill the filter with enough fuel to check the o-ring for leaks.
    • No leaks? Good, fill the filter ALL the way to the top.
    • Leaks? If you use Gary's screwdriver trick for leverage to tighten the bowl onto the filter you should never have a leak. If you do, dump the fuel back in the container and try again.
      Before the screwdriver trick, I had quite a bit of experience with the bowl o-ring leaking - no matter how much I tightened it wouldn't stop leaking. Diesel fuel is very slippery and it's hard to get a good enough grip to tighten without a little leverage.
  5. Carefully carry your filter filled with fuel over to the unit and screw it on. Hand tight is all that is necessary.
  6. IF you opened the vent plug on top of the Racor unit, (no need because you didn't drain the bowl, right?) make sure you close it!

How to change the secondary fuel filter (the one on the engine)

  1. Get ready with your absorbent sheets and a waste receptacle.
  2. Unscrew the filter (clockwise)
    • If you can't get the filter off the unit by hand, use the adjustable swivel band wrench to loosen it and then take it off.
  3. Discard the filter in waste receptacle, dripping fuel all over along the way.
  4. Pour some clean diesel in the new filter to fill it up and screw onto the engine. Yep, fuel spilling is unavoidable.
  5. Hand tighten, then use the swivel band wrench and tighten another 1/4 turn.

bleed nut
Plenty of fuel out the bleed nut, turn off the keyswitch

How to bleed the fuel system after changing the fuel filters

Tip: It helps to have someone on hand to turn the keyswitch on while you, the expert, wait for the fuel to run freely out of the injector pump bleed plug/nut.

  1. Open the fuel tank valve.
  2. Position a shop paper towel under the bleed nut to catch the fuel.
  3. Open the air bleed nut (the nut, or plug, at the end of the fuel hose that supplies fuel to the injectors)
  4. Turn the ignition key on, but don't try to start it. You should hear very fast clicking from the fuel pump as it pumps fuel. Watch the bleed nut, if you look quickly enough you might see the air bubbles come out, then you'll see a little fuel coming out. Within a few seconds you will observe plenty of fuel coming out - that means no air, turn off the keyswitch, or shout like crazy to your buddy to shut it off.
  5. Close the bleed nut and mop up any fuel spills.
  6. Start your engine
    • Push your glow-plug button in for 30 seconds
    • Push Start button
    • Yay! Starts right up!
  7. Check for leaks!

Tip: If you used the bleed nut to get the air out you should never have to crack the fuel injectors to bleed the fuel lines.

Tip: What if you need a replacement bowl for this discontinued fuel/water separator? Look for RK 20135 Kit - Bowl 220/225. $73, Oil Filter Service Inc San Diego. You can get it cheaper online if you can wait.

Photos of this project

Changing the fuel filters and bleeding the fuel lines

Getting rid of the old fuel and filters

Most marinas have a recycling area for disposal of old fuel, filters and oil. Antifreeze, no. Check for recycling centers near you.

Other resources about fuel filters

From page 29 in the Universal M25 Owners Manual


Be sure to have some means available to catch or absorb any fuel escaping during the bleeding process so that it will not accumulate in the engine compartment or bilge.

  1. Be sure there is a sufficient supply of fuel in the fuel tank.
  2. Open the fuel shut-off valve at the tank.
  3. Start the electric fuel pump by turning the ignition key to the "ON" position on models 18, 20, 25, 30, 50, all models after 1986.
  4. Model 15 has a mechanical fuel pump. Therefore with decompression on, turn engine over with starter. Crank at 10 second intervals while doing steps #5 and 7.
  5. Slowly loosen the air bleed plug on the fuel filter, letting air escape until an air free flow of fuel is evident. (1986 models see item 7).
  6. At this time, tighten the air bleed plug on the filter.
  7. Slowly loosen the air bleed plug on the injector pump, letting air escape until an air free flow of fuel is evident. Units with a self bleed return valve, open for a short period then start engine, as soon as engine runs smooth close valve. Model-12 has continuous fuel bleeding.
  8. At this time, tighten the air bleed plug or knurled knob on the injector pump.
  9. The fuel system should now be properly bled and ready for operation.
  10. Refer to starting instructions before attempting to start the engine after bleeding the fuel system.

    CAUTION: Excessive cranking with sea cock valve open can cause water accumulation in the muffler and possibly back up into the engine. Drain muffler as needed.

    Related topic: Dirty fuel filters


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