Friday, September 30, 2016

Debunking fuel in the gas tank, case closed.

Picking up from yesterday’s post:

Imagine a time when carburetors ruled the earth (or at least car’s fuel systems), and a time before emissions controls extended to evaporating fuel vapor, say perhaps in the 70s when I began my career as a mechanic, working on cars of that era and older.  Back then, in ye olden days, fuel systems were open to the environment, both in cars and in the tanks at gas stations.  That meant that water vapor could condense in the fuel tanks and drip or run down the sides and pool at the bottom of the tanks.  This is why the fuel pickups in gas stations’ underground tanks were a few inches above the bottom, and why we always used water-detecting paste on the giant tank sticks used to measure the amount of fuel in the ground.  An inch or two of water at the bottom of the tank and no one cared as long as the amount didn’t increase rapidly- it would stay down there harmlessly.  Unless, of course, you got a fuel delivery which churned up everything on the bottom of the tanks, water, sediment, whatever.  Still, it would eventually settle back down- but if you happened fill up your car while the much was stirred up you could get the nasties, including water, into your car’s tank.  And no, most stations didn’t have great fuel filtration between the tank and the pumps.  To this day I avoid filling up my vehicles if I see a fuel truck in the gas station lot- I had to deal with too many dirty fuel systems to take the chance.  And even if you didn’t get water from a bad gas station fill up you could build up water from condensation on the roof of your fuel tank settling to the bottom.

Now we have a couple of paths to getting water into your car’s gas tank, where does that take the sugar myth?  It doesn’t take a lot of water to dissolve sugar that finds its way into the tank, especially given the constant vibration and sloshing that happens in a moving vehicle, so now we can move the sugar solution along with the gasoline towards the engine.  We still have a fuel filter to deal with, but they were generally simple paper filters designed to stop solids, not liquids, so our mix of gasoline and sugar water wouldn’t get stopped there.  This assumes that the vehicle has a fuel filter at all- which is not a safe assumption if you go far enough back in time, or if you happen to be dealing with someone who bypassed their fuel filter “because it kept clogging up”.  (If you think no one would ever do something that dumb, you have probably never worked a helpdesk).

And now the fuel hits the carburetor, where a little bowl acts as a reservoir for fuel before it finds its way into the intake system.  Carburetors are full of tiny orifices, the kind that don’t like dirt, or much of anything other than clean gasoline and clean air.  Sugar water can gum things up, block holes, or settle out into the bottom of the fuel bowl- and that’s where things are no longer theoretical.  I had to clean out a few carburetors with sticky goo in them in my “gas station mechanic” days, and I recall one where we dropped the gas tank and found an ugly mess in the tank.  Sugar in the tank could, under some circumstances, be annoying.  Not catastrophic but mildly disruptive, and a genuinely unpleasant thing to do to someone.

What’s the moral of the story?  I don’t think there is one, other than exaggeration and hyperbole feed urban legends whether they’re based on complete nonsense or a tiny grain of truth.

Bottom line, don’t put sugar in gas tanks.  Not just because it won’t work, but because it’s a rotten thing to do.



Thursday, September 29, 2016

Debunked debunking, part 2

Another “debunked” automotive urban legend is the “Sugar in the gas tank will destroy your engine!!!11!” story.  Let’s take a look at this tale, and look at a few angles folks often miss when discussing it.  This myth has been thoroughly debunked, by people both smart and not-so-smart, but let’s look at it again.

First and foremost, sugar does not dissolve in gasoline.  You might be able to stir it into some kind of suspension, but it won’t really dissolve.  (Sugar doesn’t dissolve well in alcohol, either, but that’s a topic for my other blog.)  That would seem to thoroughly debunk the story by itself, and in modern vehicles in good condition it pretty much does.

Modern, good condition… I just opened two interesting views into one angle to the tale.

Second, modern (there’s that word again) vehicles have very thorough fuel filtering which will prevent sugar granules from making it anywhere near the engine.

And finally for this post, even if sugar did dissolve in gas (which it doesn’t) and sugar made it through the filter(s) (which it won’t), the sugared fuel would only flow through the fuel, intake, and exhaust systems.  I suppose it might make it into the lower parts of the engine if the pistons/rings/cylinder walls were junk but then the engine is already trashed.

Let’s talk about what could happen in the scenario above, assuming sugar did dissolve in gas and/or filtration didn’t stop it.  It is a safe bet that fuel injectors wouldn’t like it, they might gum up eventually as the sugar burned (caramelized?) due to engine heat.  I suppose, since we’re suspending disbelief, that sugar could build up on the valves and contribute to burned valves- but the operating temperatures of modern valves are extremely high and  since they’re designed to function at such temperatures that I doubt it would be a problem as the sugar would burn off without building up.  Continuing with the fantasy, maybe turbochargers and catalytic converters wouldn’t enjoy the sugar solution- but again the extreme heat would burn the sugar somewhere in the process and probably burn it cleanly with no significant ill effects.

So there we have it, thoroughly debunked.  Except maybe not.  What if we scale back the expected damage from catastrophic to annoying, and go back in time?  In the first post on debunking going back in time was also a key to understanding the battery myth.

The rest of this story comes tomorrow (really).