Thread: Something I've never quite understood...

Originally Posted by workingonit

Not a matter of being skeptical as I accept dirt and other stuff may get in through the filler neck. But then shunted along to prefilters or filters. Tanks are generally drained and refilled on a regular basis keeping up a regular cleaning cycle. Algae generally require sunlight to grow, so if present I would think it must come from outside the tank and external contaminate into the fuel - my guess is it would die in petrol or diesel in the dark and not turn into some algal mat inside your tank. I'm not saying that there will not be a case of serious contamination, but it would have to be real case of neglect or stupidity ie the stubbies in the filler neck - someone maliciously putting sand or something else in your tank. Water is the most likely from condensation (should be easily filtered) or flooding in a river crossing (unlikely if your not already leaking fuel, maybe the breather tube, and volume could overwhelm filters).

I was told of a ship full of petrol refined overseas that had to go back and forth over a period of time between Melb and Geelong refineries to unload because its cargo had some 'growth' in it and had to be 'bled' into the Vic distribution network.

DL

I worked in the oil industry very early on in life. If true then its an example of gross human error or neglect and deceit that such a volume has been contaminated and fed into regular supplies - not from some very rapid act of nature inside the tanker or what ever - and I can't see fuel companies risking their reputation by seeding their regular stock with contaminant. The only time I saw fuel being 'bled' into the system was when a foreman accidentally made a few million litres too much of 2 stroke - he paced all day worried he'd lose his job. Fuel supply and use outside Oz I cannot vouch for - met a naval officer whose job in a fuel blockade was to rope down onto the decks of ships suspected of trafficking oil - you had to watch the swell as you went, not only because of the danger of a hard landing, but that you could actually go through the heavily rusted decks.

As said earlier water in or under the fuel may cause a rust problem in steel tanks. 200 litre aviation drums had to be inspect inside with a torch. Any kind of rust saw the drum get a ding with the steel tip boot. Dinged drums were not for aviation fuel. The dinged drums however were filled with aviation fuel and labelled 'racing fuel' - same, same but differentiated by marketing and safety protocols.

You may get bacterial growth in some circumstances - no light required. Its presence in significant quantities sufficient to cause problems is likely again due to human neglect. It can be a problem in oil cooling systems associated with lathes, owners not regularly clearing the contaminated oil. The bacteria can grow between the sliding faces when tail stocks are not moved for a long time for example, causing rust like pitting.

JD is quite right in his description of what can and sometimes does, happen. You only need to run an old motorcycle to know that. However modern filtration systems will prevent serious problems most of the time.
Bacteria also can cause serious problems, as stated above. I posted an anecdotal example a while ago.

Interesting Lots of replies but no real consensus.

I can see that air getting into the system is probably the only real issue with letting the fuel get down too low but that's not really a big issue.

The idea that you'll pick up all the crud in the bottom of the tank still doesn't make sense. Even less so since once the fuel is agitated the crud is distributed throughout the fuel so you'll be picking the crud up anyway (albeit in a more diluted form but it'll still get into the fuel system and collected by the filter).

An old wives tale based on something from early motoring that has been passed down perhaps?

As it is, I rarely go below 1/4 tank when i'm out and about anyway. I maintain as full a tank as possible when I'm parked up between trips to reduce the available space for oxygen/moisture getting in and causing problems though for the reasons described in above post.

Thing is all these modern cars with in tank Fuel Pumps run swirl pots in the base of the pump
If you run your tank low and i have been guilty of this once or twice you should not have a problem but if you consistently run low and are consistently picking up **** or water you have picked up a bad batch of fuel once or more often so change your supply source .
I have run mine down to when the fuel light comes on few times and am not concerned .
Yes i drain my filter regularly as well as change fuel filters regularly and never notice anything out of the ordinary to be concerned about

When things are cold, things tend to get smaller, contract. You're a bloke. You shouldn't need to be told that.

Interestingly, things contract at different rates. i.e. a fuel tank doesn't shrink as quickly as the contents. When it gets cool, the fuel tank sucks in air, or rather, the higher air pressure outside forces damp air inside the fuel tank into the vacuum caused by the contents of the tank getting smaller at a quicker rate than the tank.

Another thing, cool air is usually quite damp, or rather, air is usually quite damp. When this air gets into the tank, the moisture tends to condense from vapour to liquid inside the tank. The drier air then tends to escape from the tank as the temperature/pressure rises leaving the moisture in the tank.

Now, if there is little fuel in the tank, lots of moisture laden air gets into the tank. If there is lots of fuel in the tank, less moisture laden air gets into the tank. This is because air contracts at a greater rate than the fuel.

If you get moisture in your fuel tank, you can get all sorts of problems i.e. metal fuel tanks rusting and leaking or rust flakes clogging fuel systems.

This is why I try to keep my fuel tanks full of fuel.

Yes. More important if you live on the coast.

For those who doubt algae can flourish in diesel...I had a Detroit powered truck in NZ...would be driving along and just die on me...filter would be full of black algae "diesel bug". Lives in the interface between water and diesel. Got myself a big racor pre-filter, and periodically treated my tank with a chemical for diesel bug. Never had a problem after that. It does exist.