Running a car low on fuel picks up crud from the tank? Fact?

[kooky guy]

There seems to be a generally accepted idea that running a car low on fuel will cause it to pick up crud from the bottom of the tank.

I was having a discussion about this yesterday and I think it must be an old wives tale these days, but a lot of mechanics still swear that it is the case.

Given that modern cars only have a single fuel pick up, I can't see how it makes any difference how low the fuel level is - it's still going to pick up any crud in the bottom of the tank whatever the fuel level. It made sense in the days of cars having a seperate fuel pick up for the 'reserve' tank.

Or am I missing something?

[kooky guy]

Sounds like the consensus is that it is indeed nonsense then.

I wonder why so many mechanics seem to still think it. My girlfriend was warned not to let her fuel run low because her carb will get gummed up with the crud from the bottom of the tank.

Excellent point about filters - I hadn't even considered those.

[kooky guy]

Mr E said:

kooky guy said:

I wonder why so many mechanics seem to still think it. My girlfriend was warned not to let her fuel run low because her carb will get gummed up with the crud from the bottom of the tank.

What is she driving that has a carb?

It was an old VW Polo. This did happen a couple of years ago, but the fact that it all came out of the same fuel pipe whether the tank was full or almost empty was just as true then!

[kooky guy]

aka_kerrly said:

Marf said:

It's bullsh-t.

A) Why would fuel manufacturers not filter out the crap before it goes into the storage tanks?
B) What do you think a fuel filter is for?
C) Where the hell do you think the fuel pickup is in your tank? At the bottom....

It's hardly rocket surgery

Lets think for a moment, NO the fuel pick up is not always at the bottom of the tank, lots of cars have lift pumps in the tank which sole purpose is to get fuel from the top of the tank and forward it to a main high pressure pump which supplies the fuel rail.

It is/was very common on cars with steel tanks to also have steel filler necks which rust and fill the tank with crud. These are often on older carb cars which have mechanical fuel pumps driven via the cam(s).

On these types of system (of which the aforementioned 80s polo fits) the tanks did have a feeder at the bottom hence crap can/will get drawn through. A lot of these carb cars came fitted with in line fuel filters in the engine bay of which I have seen dozens that are blocked so badly they prevent the car from running!!

But that would happen whether the tank was full or almost empty...