Racor Advise

[Lord Farringdon]

Hi Guys,
I have just bought this boat and need some advice regarding the Racor water separator. I am mechanically minded and quite happily repair my own vehicle including waterpumps,cambelts and heads etc but, I have never maintained a diesel and am a little unsure of the servicing of the racor. I understand of course that bad fuel may contain water (and other things) or that a half empty fuel tank sitting for a while may allow condensation to form and water to enter the fuel. I also understand that the engine will not run on water! But, what is the problem with a little water in the fuel. Does it prevent starting? Does this cause missing due to cooling of the fuel at the compression stroke? Does it just reduce power output? Does it increase power output (like water methanol injected into gas turbines), does it cause premature engine failure due to corrosion, does it cause rapid engine failure due to 'hydraulicing'?
I know that diesel floats on water and so the water will be at the bottom of the racor bowl, but what does water in the racor bowl actually look like and will I see it or do I have to test for it?
Finally I have a couple of pictures of the racor and another filter I know nothing about. I understand the primary fuel filter is the racor (first photo) and the secondary fuel filter is on the engine, so any clues as to what this other filter is for (second photo)?



Regards


Terry

 

[fwebster]

Lets start here:

Forget what you know about fuel filtration and fuel system management for gas engines.

Diesel fuel systems consist of a couple of filter, a fuel injection/distribution pump, fuel injectors and the plumbing tying it all together. Diesel engines are compression fired so the fuel injected into the cylinder can't be just dumped into the intake system like it is with gas motors. Diesel fuel must be atomized by the injector into a very fine spray. To do that, the injection pump must produce very high fuel pressures........notice the fuel lines from the pump to the injector are steel not rubber? The pump must also distribute the fuel to individual injectors when it is needed, very much like a distributor on a gas motor distributed the spark. All this means that your injectors are a very delicate and precise part and your injection pump is more like a fine Swiss watch than a fuel pump.

The reason you go to huge lengths to keep water out of the fuel is that the precision pump and injectors are lubricated by the fuel that passes thru them and the orifices involved are so small that water and sludge won't pass thru them. Neither the pump or the injectors will tolerate water without a lot of damage.

Your Racor is the first line of defense. It has a turbine design that slings water away from the fuel flow so it falls out and collects in the bottom of the bowl. If you get water in the fuel, there will be a clear and obvious line separating the fuel from the water in the bowl and you won't have to test for it. Usually, water in the fuel promotes microbial growth in the fuel tank so you will usually see not just water in the Racor but also black sludge where the microbial growth is also trapped by the Racor.

The upper filter in your photos is a sea strainer. It is there to keep grass, sea weed, trash in the water from entering the cooling system and blocking the heat exchanger. It has nothing to do with the diesel fuel system. The lower photo is the Racor primary fuel filter.

Hope that helps you understand.............

 

[Lord Farringdon]

Thanks for that fwebster. That fills a gap in my knowledge quite well and explains why I was having problems understanding what harm water could do to the engine. Water is not good for any engine obviously, but it's not the engine, (cylinders, pistons etc), its the injectors which can be harmed by water. Now I get it and it all makes much more sense.

As for the sea water filter, that's good to know. The sales guy didn't seem to know what it was, the Sea Ray owners manual is quiet on the subject, and it didn't get to the top of the list of the things I wanted to discuss with the Volvo mechs! So thanks again fwebster.:smt038

Regards


Terry

PS Subject should have read Racor Advice! Not Advise.

 

[EmJay]

Good information to know. Thanks for the explanation. I have a question though:

When I look at the second picture, the one of the Racor, the fluid in the bowl looks almost clear to me. Is that diesel fuel, or is it water?

The reason that I ask is that my Racor bowls are all filled w/a pink to reddish fluid and I thought that is what the diesel fuel should look like!

 

[earthmover17]

Diesel fuel for off road is dyed red so it looks pink. Road diesel is not dyed and looks very light bluish. Either runs just fine.
You fuel looks as it should. One must keep an eye on the racors. When the fuel starts looking dark red it's time to change the filters and the fuel in the racors.

Jack

 

[fwebster]

The original post came from New Zealand where they most likely don't have the same screwed up tax structure as the US..........the red off-road fuel does not carry 35-40 cents of highway taxes that plain or clear fuel does.

 

[Lord Farringdon]

The original post came from New Zealand where they most likely don't have the same screwed up tax structure as the US..........the red off-road fuel does not carry 35-40 cents of highway taxes that plain or clear fuel does.

Yeah that's right Frank, they don't colour our fuel down here, but I understand the marina's dilute it with water now and again just to keep us all on our toes! :grin:

Terry