Military-Vehicles: Re: [MV] What about oxygenated fuel?

Re: [MV] What about oxygenated fuel?

Alan Bowes (
Sun, 12 Oct 1997 11:57:16 -0600

Buzz wrote:

> After we have to switch to this damn oxygenated fuel my vehicles run
> terrible. Is there an additive that I can add to improve performance?
> Regards to all,
> Buzz

Hi, Buzz,

I'm not familiar with any off-the-shelf additives to counteract the effects of
oxygenated fuel, other than non-oxygenated fuel. If anyone knows of such an
additive, I'd certainly like to hear about it, too.

The purpose of oxygenated fuel (for those who might not already know) is to
reduce carbon monoxide emissions by providing more available oxygen in the
fuel-air mixture (i.e., lean out the mixture).

Typically, one of two possible oxgygenates may be added: Alcohol (ethanol,
sometimes methanol) or ether (MTBE).

This is required in certain U.S. metropolitan areas (some 35 or 40 areas, I
believe) during winter months, when temperature inversions tend to concentrate
CO and other emissions, when engines tend to run richer for a larger percentage
of the time due to the lower temperatures, and when more fossil fuels are being
for heating purposes.

Some problems related to oxygenated fuel include:

1) Alcohol allows fuel to absorb water quite readily. If it absorbs too much
water, it can result in phase separation, in which fuel separates into two
layers, one mostly gasoline, the other mostly alcohol and water. Again, this
doesn't generally happen unless too much water has been absorbed by the fuel.
Water can be absorbed directly from the atmosphere into the fuel, so it's a
good idea to run the vehicle frequently during the winter so that you can
refresh the fuel supply fairly often. Older vehicles with vented fuel systems
have more problems with this. Some corrosion problems have also been reported
due to high water content in fuel.
2) Poor storage characteristics. Oxygenated fuel deteriorates more quickly, and
should not be stored for more than a couple of months.
3) Leaner mixtures, due to having more oxygen available in the fuel. This is
not generally a problem for computer-controlled vehicles, but a few older
vehicles may require re-jetting or other adjustments to enrich the fuel-air
mixture slightly.
4) Increased volatility may increase the tendency to vapor lock, but this is
usually not a problem in the winter.
5) Possible deterioration of rubber/plastic compounds in the fuel system. This
is generally only a problem for older vehicles (like OURS, naturally) with
original soft parts in the fuel system.
6) Possible loosening of old deposits because of the altered solvent
characteristics of the oxygenated fuel.

So what does one do about it?

You could fuel up in areas where oxygenated fuels are not sold.

You could replace the old soft parts in the fuel system with newer compounds.
This is a very good idea, with or without oxygenated fuels. Generally, this
tends to happen anyway as carbs, fuel pumps, and fuel lines are rebuilt or
replaced with newer parts. Using NOS parts, however, won't solve the problem
unless they're fairly recent issue.

If you happen to be having problems with an overly lean mixture, you could
re-jet the carburetor (not always an easy task, since besides the main jet,
there is usually a power valve orifice and/or metering rod to consider, and
there are some complicated interrelationships involved, though some
experimenting may result in a good combination). Of course, you'd have to
change it back again for the summer fuel. I know one person who has two
carburetors for his old Chevy pickup and swaps them twice a year.

You might also experiment with timing a bit, especially if you're getting any
detonation (pinging/pre-ignition) from the leaner mixture, or if it backfires
through the carb.

(Salt Lake City, Utah)

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