Maintenance Q&A
Sludge and goop

By Paul Abelson, senior technical editor

Q. I have a two-part question about my Cummins N14 that just hit 1 million miles. I replaced a bad piston oil cooler nozzle, but only a portion of it came out. The plastic tip fell in the oil pan. My mechanic said it’s not a big issue. What is your opinion?

Also, if we pull the oil pan and remove debris, should we pull a bearing cap and look at bearing condition? I have only two years’ history on the motor, but all oil samples check out OK.

A.Your mechanic is probably right about the plastic tip in the oil pan. There is a screen over the intake, so the part will not foul the pump. Inert plastic will not dissolve in the oil. That said, I would opt to drop the oil pan.

You mentioned that you have just two years of records for a 1-million mile engine, leaving about 800,000 miles undocumented. As long as you have the opportunity, it’s a good time to check for any sludge in the pan and any debris that may be on the screen. If the oil was changed regularly, the chances are the pan and oil and galleries are clean. Even though the N14 has a reputation for being bulletproof, it’s always best to check.

Since your recent oil samples check out good, you probably don’t need to pull a bearing. But just because each sample says the oil is OK, you are not necessarily in the clear.

Take your last four or five oil analysis reports and, using plain graph paper or a computer spreadsheet, plot the values for lead, copper and tin, the components of bearings. Plot miles across the horizontal axis and parts-per-million on the vertical axis.

If the line connecting the dots is fairly flat, you have no problems. If there is an unexplained spike or drop in any of the elements, it could indicate future troubles. Then you might want to examine your bearings.

Q. My ’04 Freightliner Coronado keeps losing power. I took it to my dealer, and he said there was “goop” in my fuel system. He wants to take down my fuel tanks to give them a thorough cleaning and flushing. That costs a lot of money. I wonder if you could recommend a product or something to absorb the “goop.”

A. The “goop” in fuel tanks that fouls and plugs fuel filters is a combination of bacteria and fungus. These airborne organic rascals are drawn into the fuel tank through its vents. They mix with the moisture in the air, and enter the fuel when the humidity condenses as the tank cools at night. Water is heavier than fuel, so it sinks through the fuel to rest at the bottom of the tank.

The organics get oxygen from the water below and nourishment from the hydrocarbon fuel above. There they thrive, multiplying and forming colonies. As these colonies join together, they form a slime that gets drawn into the fuel intake tubes. The slime is caught in the fuel filters as they do what they’re supposed to do: keep foreign matter out of the fuel system.

Eventually, the slime builds up on the filters in volumes sufficient to clog them and severely restrict fuel flow to the engine. That’s why you keep losing power.

That’s when it’s definitely time to change your fuel filters. But you can prevent this slime buildup, or at least delay it for a while.

First, drain your tanks. Make sure you capture the diesel in a container, in an environmentally friendly way. The first thing to come out of the drain valve should be water, followed by the slimy organic material. When pure fuel starts to drain, shut the valve. Then treat your fuel with a biocide.

Biocides are powerful chemicals and may be highly toxic. I suggest that a professional do the work. But if you want to do it yourself, you can buy some fairly strong biocides for diesel fuel at a parts distributor or a boaters’ supply store. A few that come to mind are from Racor, Penray and Biobore JF.

First, read the label and make sure you understand all of it. Follow the instructions to the letter. Always wear protective clothing, including long rubber gloves and full eye protection – goggles, not just glasses. Sometimes respirators or mouth and nose filter masks are required. The label will tell you what is needed.

Add the biocide to the fuel in the proper ratio. Then run the engine in normal service, but try to get the tanks as close to empty as you can. The insides of your tanks should now be fairly clean. Inspect the tanks. If any patches of slime remain, wear protective gear and remove them with a long-handled brush. The tank need not be perfectly clean as long as any residual slime is small and localized.

Then decide on a fuel conditioner and stay with one brand. I recommend buying ahead and keeping a supply in your truck. Any of the popular brands will do the job.

Treat the fuel at every fill-up, even in summer. The conditioner will control water and will help “starve” any organics that get into the fuel. It will also help keep the fuel system, including injectors, clean and lubricated.

At every PM, check your fuel filters for signs of slime buildup. If you treat regularly, they should be minimal. Treat your fuel with a biocide twice a year, spring and fall. And always buy fuel at high-volume brand-name truck stops. There’s a reason bargain fuel is cheap. Often, it’s surplus fuel that has been stored too long and has begun to grow its own organic slime. LL

Do you have a maintenance question?
Send your question to Paul Abelson, senior technical editor, in care of Land Line Magazine, PO Box 1000, Grain Valley, MO 64029; email them to or fax questions to 630-983-7678. Please mark your message Attention: Maintenance Q&A. Although we won't be able to publish an answer to all questions in Land Line, we will answer as many as possible.

Senior Technical Editor Paul Abelson is a life member of OOIDA, holds an Illinois CDL, is active in the Technology & Maintenance Council, and is a recipient of the Lifetime Achievement Award from the Truck Writers of North America.