Perkins 4-108 fuel turns black

[Tweeds]

I have a Perkins 4-108 with 5400 hrs (2400 since over haul).. Since owning the boat the fuel as observed in the Racor bowl turns dark (black) and when drained and inspected I see no solid particles but it looks like oil is getting into the fuel. I have had the fuel polished and emptied and cleaned the tank twice in the last 3 years and the fuel still turns dark in my Racor filter bowl after running through a half tank or 25 gal of fuel. I use about 1/2 qt of 40 wt oil every 24 hours of motoring.

I am currently in Mexico and buy clean fuel from Pemex and use a Baja Filter and Biobor? conditioner. About 100 motoring hours ago I used the Howes? fuel conditioner and the fuel now remains relatively clear although still a bit darker than when I fueled.

My question is what is turning the fuel black or can oil get in my fuel and if so how? Could it be entering my injector pump through a worn out seal?

 

[catserveng]

The small Perkins has a pretty low fuel return rate, and it is unlikely the lube oil is gettting into the return fuel.

Usually fuel darkening is a sign of oxidation or biological growth. I know you said you have used Biobor but if a tank is badly infested, it may not be enough.

Have you thought of sending off a sample to a lab? There are also some off the shelof "bug test kits" for fuel, this link is to a site for a product used buy a lot of our pleasure craft customers.

http://www.dieselcraft.com/productinfo_4.htm

You can also try getting a container of known clean fuel, and run the engine out of it for a while, and see if it becomes darker just going thru the engine, just put the supply and return line into it and run it for a while, could help determine if there is a transfer of lube oil to the fuel.

 

[zeusfaber]

Is it worth smearing some on a slide and putting it under a microscope. Soot and wear particles look a bit different from biological contamination.

A.