Bleeding 4-108

[jimisbell]

Originally Posted by GordMay

As previously mentioned (Steve Kidson, pwederell & Alan Wheeler), you don’t want a filtre in the fuel return line.

Why??? The reason that related to size is not valid as it can be changed. I have a 10 micron filter on the engine and the other one is a 5 micron filter. but these numbers can be reversed. BUT why no on the return line as it wont take long for the fuel to ALL be filtered.

As to what happens when the engine mounted filter clogs, been there done that and the coast guard towed me in.

I had a new tank put in last spring and all new lines but the filter that the PO had told had been changed a month before...Hadnt. Dont trust ANYONE!!!

[DeepFrz]

Jim, IMHO, you are better off building a fuel polisher rather than filtering the return line. Actually that line has already been filtered twice. A polisher should move a rather large amount of fuel through filters that have the capacity to handle the volume. The pickup and return line should be at opposite ends of the tank and close to the bottom of the tank. Actually they should be closer to the bottom of the tank than the engine pickup line. With a fairly high capacity pump you will set up a scouring action in the tank so you have a better chance ot keeping the tank clean.

[Alan Wheeler]

Why???

Because the return line requires a non-restrictive or unempeded return to tank. The return line is more important to pump cooling than jsut having somewhere fro excess fuel to go. The return line allows a flow rate so as a volume of fuel can be allowed to cool the pump. restrict that line and your pump will over heat and a hot pump means poor lubrication. There maybe a enough flow through a clean filter, but if that filter clogs, then the flow will be reduced.
Secondly, that side of the fuel pump was never meant to experiance a great deal of pressure. Not sure of yours, but, Many pumps have the return line from the top of the pump housing. There is a thin plate with a very small gasket on the top that covers a bath of fuel. Place that part of the pump under pressure, and you will end up with it leaking.
Thirdly, polishing the return fuel after it has gone through the pump is a little silly. Particles have already done there job of wearing close tolerance parts. You are far better placing that filter in the supply line where it can do the same job as you want to do, PLUS the added job of keeping finer particles out of the pump right from the get go.
I guess it's like saying, you have the ambulance at the bottom of the cliff

[GordMay]

Steve D’Antonio on Fuel Polishing Installation:

I’ve found that the majority of fuel polishing systems I encounter here in the boat yard (other than the ones we install ), are not plumbed in such a way as to maximize their efficiency. That’s a fancy way of saying they are often strangled by undersized plumbing or they are incorrectly plumbed to the tanks.

For a fuel polishing system to work as well as possible, two criteria must be met. First, the plumbing should be entirely independent from any existing engine or generator fuel supply or return plumbing. Why? Existing plumbing fittings are often too small to handle polishing system volume and the polishing system plumbing may compromise the engine or gen’s fuel supply or impede its return (this can cause injector pumps to malfunction). Second, the polishing system’s supply and return plumbing inlet and outlets should both be located close to the bottom of the tank. This ensures that the debris and water are being picked up by the polisher and it sets up a current that will scour the bottom of the tank, picking up loose debris. Additionally, the problem with returning fuel to the top of the tank, for both polishing systems and engines, is that the splashing created by this practice aerates the fuel. Air entrained within the fuel, if it should make it to the injection system, will cause erratic operation and it hastens the fuel’s oxidation, which essentially makes it age more quickly.

Given the choice, I prefer to install fittings at or near the top of the tank and then utilize drop tubes the draw and return fuel from the tank’s bottom. This minimizes the possibility of leaks and still ensures efficient fuel polishing.

Steve C. D’Antonio

[avazquez]

Originally Posted by Steve Kidson

I put priming bulbs in the fuel line between the tank and the first filter. Found it to be very sucessful in quickly and painlessly pumping fuel through lines.

Fair winds

Steve

My 4108 had a priming bulb, one of those used in outboard engines. I removed it when I replaced all fuel lines but I will re install it because it was great..........much much better than the one in the perkings engine.

[Maddog]

I have a Racor filter at 20 Microns as a primary. It has a built in primeing pump that I use to prime the filter and bleed the whole system to the injector pump. The filter on the engine by the lift pump is a 2 micron. All the hoses were replaced last year. This system has served me well. That little pump on the racor allows me to bleed my system in less than 5 mins. A quick crank for the injectors and I am through in less than 10. I forget which Racor I have. It is not the FG-500. Its the smaller one were the filter is contained in its own elemet and the plastic inspection bowl screws on the bottom, It may be the 320.

[lovinlife]

Make sure that none of the ends of your fuel hoses are damaged where the hoseclamps fit, its often good to just cut off all the ends just to be sure, that is if your fuellines are long enough, i've had said problem on a few different occations