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Old 31-01-2012, 17:16   #1
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Protocol for Changing Fuel Filter

OK, when we first bought this boat I had a mechanic service the engine and show me what he was doing and why. It cost more money than it normally would but I was happy to pay extra and learn how to do things properly.

One of the tasks was changing the fuel filters (Racor primary filter and CAV secondary filter on a Perkins 4.236). The Perkins handbook for the engine lists the procedure and it was exactly as I was shown with bleeding air from the fuel system afterward.

I've recently been told by 2 mechanically savvy types that when changing a fuel filter it is imperative that the new filter element be flooded with diesel prior to fitting in the filter housing. Failure to do so will apparently make bleeding the fuel system impossible.

So which protocol is correct? Flooding the filter element with diesel first or not? Does it really matter? not flooding the filter elements hasn't stopped me bleeding the fuel system so far. Is this a trick that not everyone knows?

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Old 31-01-2012, 17:36   #2
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Re: Protocol for changing fuel filter

All kind of depends on several things.

1. Location of the fuel tanks vs the filter and engine. If the tanks are higher than the filter then just opening the bleed screw the filter should fill without any help.

2. What kind of engine. Some do pretty well priming themselves.

3. What kind of pump do you have on the bleeding system. Some work a lot better than others.

Bottom line, it never hurts to fill the filter housings with diesel, whether they gravity fill themselves or you have to do it by hand. But if whatever you are doing works then don't worry.

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Old 31-01-2012, 17:44   #3
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Re: Protocol for changing fuel filter

If nothing else it saves a lot of time bleeding air. If you have no gravity feed it is normal procedure to fill the filter element/housing yes.

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Old 31-01-2012, 17:46   #4
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Re: Protocol for changing fuel filter

I just went through this with our Raycor primary on our Yanmar 3GM30F. My primary is located slightly above the fuel line. At first, when I put the filter back together, the Raycor filter and bowl were empty. I tried bleeding the system by pumping the manual pump lever. I didn't see any fuel/air escaping from the first bleed screw nor did I feel that fuel was flowing. The manual pump felt limp.

What I did was disconnect the fuel input line from the Raycor filter and drain about 1/2 fuel into the filter/bowl. All I had to do was move the filter/bowl below the level of the fuel line and fuel drained naturally. I reassembled and repeated the pump/bleed process. This time I definitely felt pressure on the pump and saw fuel/air escaping from the bleed screw.

When I did the secondary filter, which is located below the heat exchanger, I also did not fill the filter with fuel. This time, the pump did circulate fuel and I could bleed from the second bleed screw.

Overall, I was pleasantly surprised at how easy it was to bleed the air from the system. Afterwards, I ran the engine about 20 minutes just to make sure there was no air remaining in the system.

My feeling is that my primary needed to be partially filled to circulate fuel; while the secondary did not. As skipmac said, probably due to the height/location of the filters.

A couple other things I've learned - to minimize spilling diesel I would try to unscrew the filter and bowl together. I didn't want to reuse the diesel as it had black sediment. It might be useful to have a 1/2 pint of clean diesel to refill the filter/bowl. In my case, draining fuel worked well.
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