color of fuel - PeachParts Mercedes-Benz Forum

pdxman · #1 09-04-2003, 11:36 PM

Okay, I noticed this before when first changing my filters awhile back on my 240D that the fuel color in the pre-filter was a darker, sooty hue. Thought it was normal. Then I got my 300D and looking at the pre-filter it is staying the same shade of light green when filling up.

Now I know you guys, and myself, that the first thought is...algae. I've read through the archives on other posts about this and the discussions are on slimy green things and blobs, clogged filters, etc...But I am not thinking this right now. I just bought myself a new pre-filter and cut open the old one for inspection. All I found was a small amount of fine grit (tank rust probably) and nothing resembling algae or slime.

Here's my question...Could the unused fuel returning back to the system somehow become oily or sooty and therefore darken the fuel color? What would cause this and is it normal?

Thinking caps on please?

P.E.Haiges · #2 09-05-2003, 12:14 PM

pdxman,

I don't see how the return fuel could become contaminated. I only flows thru closed hoses and fuel lines external to the engine.

P E H

pdxman · #3 09-05-2003, 01:46 PM

I've read in past posts that the injection pump contained oil. Could that be a possible source?

dabenz · #4 09-05-2003, 07:47 PM

pdxman, if you're getting the fuel from the same source at the same frequency for both cars then the issue is probably crud in the tank or the rubber parts of the fuel line system starting to degrade. It's possible that injector pump oil could get back to the tank, but you'd have to have a strange internal leak and a noticable drop in oil level if you drive the car frequently. Trace your tank return line upstream from the tank to see what I mean. Also check the inside of the fuel filler cap to see that the gasket is intact.

Holson Adi · #5 09-05-2003, 11:03 PM

I had the same problem. The fuel in the pre-filter was dark green/gray. After I put a tube of Biobor Diesel Doctor and replaced the pre-filter the fuel has been yellow and very clean.

pdxman · #6 09-06-2003, 02:07 AM

My first thought was algae and adding some bio-stuff (which I haven't found retail yet). anyway, I think it may have something to do with rubber. I replaced the leaking hoses off the fuel tank (3) with OEM months ago. But the cigar hose I replaced with regular black hose. Not sure if it was fuel rated and got it at a auto parts store. Could this rubber be reacting with the diesel and cause the discoloration? Would it harm engine parts or cause other problems?

dabenz · #7 09-06-2003, 09:56 AM

pdxman, ask for biocide/algicide at RV stores, marinas, major semi-truck service centers (Peterbilt, Freightliner, etc.), agricultural stores, or NAPA. Ask and you'll learn who wants your business. Go to Powerservice's web site for a description and/or part number if the NAPA folks in your area play dumb (yes, NAPA really can get it for you and quickly too). Do this after you put the proper fuel hoses on and do the fuel filter change. Fastlane can get them to you fast, and they do provide this wonderful "free" web site for us.

P.E.Haiges · #8 09-07-2003, 10:41 AM

Pdxman,

You should see the color of my fuel since I started adding about an ounce per gallon of used engine oil to the fuel. Its amazing how such a little used oil can turn a gallon of fuel oil so black.

This is an experiment I just started and I will keep the readers posted on how it works. Burning that small amount of oil in my tractor engine, I can't see any difference in the exhaust smoke.

P E H

bjcsc · #9 09-08-2003, 06:56 PM

P E H:

Not to hijack this thread, but re: 1 ounce of oil per gallon of fuel, I am wondering what your hypothesis is...

P.E.Haiges · #10 09-08-2003, 07:44 PM

bjcsc,

I don't believe in wasting anything and I have a lot of used engine oil. So I thought I might as well burn it in the engine. I should help the IP also by lubricating it better.

The only thing I am wondering about is if it will plug the fuel filters. I'm about to find out. I filter the used oil well before I put it in the fuel tank.

I drove the 300SD today for the first time with the "fuel additive" and I couldn't notice any difference nor did I see any smoke. The amount I use would be equilivant to about 750 miles per quart.

P E H