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Old 27-03-2008, 09:25   #1
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Tell me about my primary fuel filter

So I'm aware that I need to bleed water and sediment out of my primary filter but last weekend attempted to do so and got a little confused. I've searched online for information but suspect its so obvious that no-one bothered posting it. Please breathe a sigh of "omg what a noob" and then set me right here!

I've attached a picture of the filter, perhaps not the best angle but hopefully enough to give you the idea. Under the metal bowl is a bolt and on that bolt is a nut that looks like you should be able to either hold it with your hand or undo it with your hand. Mine seems stuck (then again my fingers were fractured in rugby the day before trying it). When I undo the bolt itself fuel does drain out but not in any form of control, filling the bowl, dripping from around the edges of the large nut, totally missing the waiting bacardi bottle I was trying to catch a sample in. At the same time air was leaking in - not too much but how am I meant to drain air from the primary filter, unlike the secondary there is no obvious bleed screw on top.

While you're shaking with laughter at my obvious naivity in all things diesel I have a few more questions:
-Is the colour of the diesel in the filter good? To me it looks kinda murky (so does the stuff in the tank but there's fifty gallons of it and I was hoping to burn some off before emptying and cleaning).
-When I change the filter I presume I can simply take the top off and drop a new one in, perhaps closing the fuel supply off and draining the chamber so I can clean it at the same time. Roughly right?
-Whats the point behind the metal bowl? It seems to just obscure the view of the most interesting part of the filter - the bottom.

I can't believe I'm asking a question too simple for any of my Don Casey books to bother answering!
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Old 27-03-2008, 10:33   #2
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The fuel is probably not draining out because of a vacuum lock unless there is a LOT of sludge in the bottom. Try loosening the t-handle which you will have to do to remove the top to install an new filter.

This looks like a Racor 500 filter. To do a thorough cleaning it should probably be completely dissasembled to clean the sludge out of the lower bowl. Be careful there are some small loose parts including small balls that work as check valves.

Once reassembled I usually pour fresh diesel in from the top until full and then replace the lid. This will leave some air but you are probably going to need to bleed the engine anyway.

I wouldn't be too concerned about the murkiness, a bit is not uncommon.

If the diesel has been sitting quite a while a fuel polishing service might be the way to go. They will suck the fuel out of the tank through filters and then pump it back into the tank over and over until the filters show clean. A good service will also vacuum out the bottom of the tank to remove any sludge on the bottom. Goop in the bottom of the tank will get stirred up in choppy water and invariably plug your filters just when you can least afford to have the engine die.

The metal cap serves no real purpose. Some models have them some don't.

Good luck, hope this helps.
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Old 27-03-2008, 11:10   #3
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Hi, Tom.

No one's going to make fun of you for asking questions like these. We've all been there at one time or another.

When I drain my Racor 500, the same thing happens, even with the top off. The fuel rushes out and splashes a bit. I put one of those absorbant pads with a plastic backing under it--the kind used in the beds of incontinent people. They're about 30" square, and catch everything. I use a wide-mouth plastic cup to catch the fuel coming out.

A hand-operated valve is available that replaces the nut on the bottom of the plastic bowl. Unfortunately, I don't have enough room to install one on my rig. I believe Racor sells them as an accessory. Things would be a lot neater and more convenient with one of those.

WARNING: whatever you do, DO NOT re-tighten the drain nut so tight that you crack the plastic bowl. It's easily done. Even a tiny crack will let air into the fuel system and create problems for you.

The fuel should not be cloudy after you clean out the filter case. If fuel coming from your tank is cloudy, you should consider paying a "fuel polisher" to come and clean your fuel.
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Old 27-03-2008, 13:11   #4
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Thanks guys.

Fuel polishing sounds good, if not complete replacement. There's about 50 gallons in the tank and the previous owners of four years said they only put in a total of about 20 so some of that juice has got to be pretty old.

If I'm going to have to bleed the engine anyway (think I'll get lucky and restrict this to the secondary filter?) then it sounds like I may as well empty the primary filter, put a new filter piece in and clean it out a bit. This time armed with a bit more info.

Will the fuel lift pump drag the air in the primary filter through to the secondary filter where I can bleed it? Won't it float around at the top of the primary filter until rough seas allow it through at exactly the wrong moment?
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Old 27-03-2008, 13:29   #5
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There are two methods (that I know of) to fill what you call the primary filter, that is the Racor fuel/water separator.

The first is to have a small jug of fuel and fill the filter to the brim before putting the cap on and tightening it. Not torqued down with a cheater bar but snug enough to stop air leaks.

Another method is to install a fuel primer bulb, such as those used on the fuel lines for outboard motors, between the fuel tank and the Racor. Put the lid on the filter but leave it a bit loose and then pump the bulb until fuel starts to seep out around the edges. At that point snug down the lid.
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Old 27-03-2008, 13:44   #6
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Quote:
Originally Posted by cabo_sailor View Post

The metal cap serves no real purpose. Some models have them some don't.
Everything has basically been answered. One thing I wanted to add is the purpose of the metal bowl vs. a clear plastic bowl.

The metal bowl is specified by ABYC as required if the fuel filter is in the engine room. This prevents (to some degree) flames from an engine fire from melting your fuel filter, and allowing a lot more fuel to spill into the fire.

A metal shield is also acceptable, from what I am recalling... fuzzy recall, but that's what I'm remembering.
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Old 27-03-2008, 16:06   #7
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Plus, when you rear back with a hammer to "fix" something else on the diesel you won't crack the bowl.

Not sure if that is ABYC or School of Hard Knocks.
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Old 27-03-2008, 17:46   #8
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Originally Posted by theonecalledtom View Post
If I'm going to have to bleed the engine anyway (think I'll get lucky and restrict this to the secondary filter?)...

...Will the fuel lift pump drag the air in the primary filter through to the secondary filter where I can bleed it? Won't it float around at the top of the primary filter until rough seas allow it through at exactly the wrong moment?
Many engines will self prime without bleeding and is always worth a try to check if so.

Our own (a Volvo Penta) will self prime after replacing both the primary and secondary filters together and just fitting them full of air - that even though the fuel tank is below the engine (it is in the fin keel). Starts immediately, sometimes gives a couple of coughs and splutters for a few seconds but works every time.
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Old 31-03-2008, 18:30   #9
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Replaced the filter this weekend. Couldn't get the bowl off - left that for another day but I managed to do a reasonable job I hope of cleaning the gunk out of the inside with a clean toothbrush, an improvised implement made from a clear plastic packaging container and multiple rinses of diesel. Will be interesting to see how has returned next time I do that.

For anyone else about to do this for the first time I'd like to point out that once you have disconnected that bottom bolt things gush out rather than dribble. I'd say I dropped a fair amount of diesel as I got caught by suprise when the whole thing fell apart! Other than that it was all pretty straighforward, bar not being able to take the bowl off. Certainly not a housekeeping task to worry about.

Didn't check to see if my system is self priming, being a coward I filled back up to the brim as the filter instructions suggest. Engine still runs so hopefully I did okay.
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