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Mystery of the "Black Goo" -- Solved?

The Mystery of the "Black Goo" -- Solved?

Since the first day a gear-head decided to try running e85 in his carbureted engine the question has been around. What is that black goo that seems to form in my intake after a couple weeks? While it doesn't hurt anything, it has long been a subject of conversation and even argument among us "ethanol heads." The answer to this question isn't a simple one, but here is some information that should help solve the mystery.

There are actually a few different causes of black staining of components used in and around ethanol fuel systems and inside engines. The first step is to identify which source you are seeing. In this article we are offering some pointers on how to identify and even eliminate these sources. There may be other sources besides what is discussed here, but we are covering the most common ones. Special thanks go to Nick Rice at Carbon Green Bio Energy in Lake Odessa, Michigan for his help in this area and for his continued support of the racing industry.

Coked engine oil is probably the most common that is seen inside an engine. This is not unique to engines running on ethanol fuels and is fairly easy to distinguish from other sources. Engine oil based deposits are most commonly seen on the back sides of intake/exhaust valves and sometimes in exhaust ports, not usually in the intake plenum only. The solution to this issue is checking and correcting valve guide and valve seal wear problems. Reducing reversion caused by a large race camshaft can also help with this problem as well as solving oil drain-back problems in the cylinder heads.

Oil on intake valves can be confirmed by trying solvents to remove it. Typically cooked on oil is very difficult to remove with solvents (carb clean, brake clean, acetone, etc) and is usually most easily removed mechanically. The tell-tale burnt oil smell when scraping it is the tip off!

Distillers moss, also known by its Latin name as Baudoinia Compniacensis, is a black fungal growth that grows in the presence of airborne ethanol vapors. Yes, I said fungal! Really. Distillers or brewers moss can be seen growing on storage tanks, trees, street signs, even aluminum siding on houses near distilleries. It could also pop up on leaky fuel drums, fuel tanks, fuel lines, etc. This growth is black and crust-like in nature (not sticky) and unlikely to be observed inside an engine. This species is actually killed by gasoline in concentrations above 10% so it will not grow inside fuel cells or lines that contain e85. Power washing or scrubbing with soap and water easily removes the growth.

The newest culprit that we have learned about inside the intake tract of an engine is what is referred to as drag reducer. Drag reducing agents (DRAs) and drag reducing polymers (DRPs) are used by refineries to aid in the transportation of crude oil and gasoline through pipelines by reducing friction on the pipe walls and reducing turbulence. These black gooey agents are added as a suspension at pumping stations on pipelines and they remain in suspension until the fuel is burned unnoticed in a gasoline engine. However, recent information suggests that the current drag reducers used in pipelines will settle out when in the presence of high concentrations of alcohols and diesel fuels.

The buildup from DRAs and DRPs will typically show up as a tar-like coating in the bottom of an intake plenum of a carbureted engine or at the tip of fuel injectors in an EFI engine. These drag reducing compounds can also settle out in the bottom of diesel fuel tanks (but not e85 fuel tanks). The substance is easily dissolved by oil based substances like WD-40 or gasoline. Carb clean and brake clean will also remove the buildup, but it is most easily removed with a light oil based product. So now the $2.00 a gallon question . . . how do I prevent that black goo from building up in my intake plenum?

Until a new drag reducing agent is developed and implemented by the oil companies that properly remains in suspension in high percent ethanol/gasoline blends we may be stuck with the problem. Fortunately we have not seen any performance difference when there is a slight to moderate buildup in an intake and the buildup does not typically go down far enough into the intake ports to cause any trouble in a carbureted engine. We do suggest cleaning your plenum and bottom of your HPI carburetor yearly as a precaution to prevent excessive buildup.

If this yearly cleaning bothers you, one possible solution is to mix your own e85 using e98 and gasoline that has not traveled through a pipeline and does not have drag reducers in it. Ethanol does not have DRA's in it since it is not typically pumped through pipelines so we are only "worried" about the 15% gasoline part of e85. Racing gasoline probably does not have the drag reducers, but only the fuel manufacturer can say for sure. It depends on what the race fuel manufacturer uses for blend stock and whether that blend stock has traveled through a pipeline or not.

Unfortunately, mixing your own e85 is not always a practical solution and defeats the purpose of running an inexpensive high performance fuel unless you have an inexpensive source of e98 nearby. Remember, only use UNLEADED gasoline to mix with ethanol! Tetraethyl lead is a knock antagonist in the presence of ethanol fuels. In other words, the octane rating is lower when lead is mixed with ethanol rather than raised when it is mixed with gasoline.

Another option is filtering. Fuel distributors have reported that the DRA's and DRP's have clogged the filters on the station's e85 pumps on occasion. These pump filters are usually 5 micron filters so running your fuel through a 5 micron or smaller filter when filling your fuel cell from a drum should help remove them but we have not tested this idea yet -- please let us know if you do! It stands to reason that if the drag reducers can clog up a 5 micron filter, then a 5 micron or smaller filter should help remove more of them from your fuel and slow down any buildup.

IMPORTANT NOTE: We do not recommend running a small micron filter like this in your cars fuel system because when it clogs it will severely limit fuel supply to the engine. A small micron filter would have to be used on the fuel pumping system -- possibly between your 55 gallon storage drum and your fuel cell.

*** New info 2/2/2018 -- since we made some of the information in the article public last week we have had a large ethanol supplier contact us with additional information about the source of the "black goo." He states that he has seen black buildup from the denaturant used in e85. Some e85 suppliers use liquefied natural gasoline for the 2% denaturant in e98 and also as the 15% gasoline component. While we have not had time to test and verify this information, we wanted to publish it with caveat so you can decide for yourself.

We hope this information helps and, as always, feel free to contact us at HPI if you have any questions!

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Eric Niefert


8695 Hanna Lake Ave SE
Caledonia, Michigan 49316


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