Will someone tell me why my gas tank has no rust, yet

[Geo-TH,In]

Will someone tell me why my gas tank has no rust, yet the metal carb bowls on my champion generators rust?

To prove the red material on the aluminum part of the carb is rust, I put the part of the carb in bleach.

The bleach turned the rust black and I was able to wipe it off with a paper towel. If the reddish material were varnish, would bleach remove it?

So I want to know why the metal inside the gas tank is rust free and the carb isn't.

Some are going to blame ethanol.
When I was a kid, decades before ethanol, I would buy honda motorcycles that sat for a long time.
The gas tanks and carbs were full of rust. So using ethanol as an excuse for rust is questionable.

I decided to turn the gas off and run the generator until it ran out of gas. Then I used a 10mm wrench and loosen the bolt holding the carb bowl in place. Some Gas ran out of the carb.

So in the future when I'm done using my generator, I'm going to turn my gas off and loosen the bowl bolt. Next day, I'll tighten the carb bolt.

If the metal gas tank doesn't rust, why can't they make a carb bowl that doesn't rust??

I don't use my generators very often, so once a year I drain the old gas and replace it with new gas.

I don't have carb issues with my lawn mowers, tiller, terramites and my antique tractors. I leave those carbs full of gas year around.
I only have carb issues with my 3500 w Champion generators. Grrrrrrrrrrr,

I wonder, will a grounding rod prevent rust?lol

 

[MarkB_MI]

George, I wasn't aware household bleach (Clorox) will remove rust. I have no idea how Clorox reacts with varnish, either. But those deposits sure look like what you get when gasoline evaporates.

 

[Geo-TH,In]

Mark,
That carb is about 10 years old and has always been full of gas, never empty. The gas tank has always been full of gas.

Phosphoric acid will also remove the rusty looking stuff on the plastic float, metal bowl and aluminum.

I think most carbs on other small engines are aluminum. Perhaps my 20 hp briggs has a metal bowl. Not sure. My 2 20 hp briggs have NEVER had carb issues. In the spring, I use all last years gas in the tank before adding new.

I conclude there is something wrong with the metal used to make the bowl on the generator. So I will try draining all the gas from then when I'm not using them. Keep a 10mm wrench handy.
Good thing the carb bolt is easy to get to. Good think replacement carbs are CHEAP!

 

[Hobo,NC]

Yes some of it is rust are a reaction from the bowl, some and most is from the fuel and it came right out of the station tank. You cannot pump,haul and store it without some contamination its just not possible.

I have cut hundreds of automotive fuel filters apart even with a plastic tank what you see is what you get. Of course some of it comes from the vehicle delivery system but not all of it.

I try my best after I have drained the carb to get WD40 into the bowl for storage. On my pressure washer I go as far to suck all the fuel out and get a little 2 cycle mix in the tank to coat it. I can deal with a qt of fuel but 5 gal I just deal with the carb bowl : )

Fuel is dirty its part of life, convert to NG are propane life will be good.

I worked on a B&S 19.5 lawn mower carb yesterday GRRRRRRR. It was not mine that made it worst *^%$$... On a side note fuel injectors screens get stopped up with the same stuff, its everywhere if you are lucky it passes it.

This post was edited by Hobo,NC on 07/09/2023 at 06:36 am.

 

[John T]

Mornin good neighbor, as always GREAT QUESTIONS, thanks for posting your always interesting technical and engineering questions ........... .

Will someone tell me why my gas tank has no rust, yet the metal carb bowls on my champion generators rust? .. .

Sorry, I'm no materials expert or chemist nor have I googled it, hopefully someone here is one of those or will be kind enough to research it and post their findings ..

HOWEVER FWIW I can tell you steps I have taken which seem to help reduce carb rust.

I'm a user and believer in adding Sta Bil for long term storage and add it to my tank and run the engine BEFORE draining out a carbs bowl prior to storage. I have also at times NOT drained a carbs bowl after adding Sta Bil then running the engine and I cant prove or disprove it made any huge difference ????????

IN ADDITION to adding Sta Bil I HAVE ADDED SOME TWO CYCLE LOW ASH SUPPOSEDLY ? COMBUSTIBLE OUTBOARD MOTOR OIL. MAYBE that leaves a thin film oil residue that MAYBE coats carb surfaces that MAYBE helps reduce rust ???????????? Ive done it, seems to help but hard to prove or disprove.. .

NOW QUESTIONS for you George and others..Oxidation (rusting) requires oxygen right ?? So if a surface such as the tank or carbs bowl are filled to reduce oxygen contact wouldn't that help reduce rust ??? .. .

How does that cut in favor of or opposing draining a carbs bowl prior to storage ??

Fun thread thanks to all who respond and have a great Sunday everyone

John T A retired yet ever curious engineer and happy contented camper yayyyyyyy

 

[Steve@Advance]

My guess is the tank has some type rust resistant coating, probably electro galvanized.

This was probably done as a safety measure with gas being stored directly above the engine in an application that is often left running unattended.

The carb bowl is also a low point that gathers water, even with ethanol, it still will gather water. The only true way to get rid of all the fuel when storing is to take the bowl off and dump it. Even loosening the bolt will leave some liquid in the bowl.

 

[Geo-TH,In]

I thought ethanol would absorb any moisture in the gas.

Don't they make an ethanol tester? You see how much water the ethanol absorbs?

 

[jimg.allentown]

What you are getting is not necessarily rust. It coiuld be a result of galvanic corrosion or just deposits from additives in the gasoline that are left behind reacting with the bowl.
You use the term ''metal.'' ALL of it is metal. Metal can be aluminum, steel, cast iron, copper, brass or pewter. It is all metal by definition.
Gas tank is probably made of a different alloy than the carburetor bowl. Most carburetor bowls that I have looket at seem to be made of a thin sheet metal like tin or steel. The corrosion you see is possibly from something that is not compatible with modern fuels.

Also, just a suggestion, you might want to make your subject lines a bit shorter and more concise rather than trying to squeeze the entire post into the subject line. Long subject lines are one of the things that causes the broken threads.

 

[DoubleO7]

The vast majority of small engine carbs are a zamak (mostly zinc) pot metal diecast part. Not aluminum because the hotter aluminum will ruin the molds sooner and the aluminum is more expensive to buy and melt.
I am really surprised the they are still made of any metal vs plastic.

The bowls are also virtually all sheet metal steel and electroplated.

So was the bowl rusty inside or just covered in a rust particles?

A China carb likely does not spend the same amount of time in the plating process as an oem carb.

 

[DoubleO7]

(reply to post at 10:35:03 07/09/23)

My guess is the tank has some type rust resistant coating, probably electro galvanized.

The better steel fuel tanks use terne plated steel.

 

[Russ from MN]

I used to have a problem like that, now when our generator is in storage it has a little mixed gas in it, 50-1. When ever we use it it gets filled with E-10, but when I'm done I put some 50-1 in it and run it a little, then run the carburetor empty. That has worked well for me, we seldom have power outages, but I test run the generator twice a year.

 

[john in la]

Mark. I dont believe his carb bowl is even made of metal so it can rust in the first place. Many are made out of stamped aluminum and aluminum doesnt rust like metal does.

But I could always be wrong so I asked George to first prove to us the bowl was metal and the deposits in the bottom were actually rust by picking up the deposits with a magnet.

 

[kencombs]

Geo, I'm not positive but don't think the bleach test proves it's rust. because as far I know bleach is not an effective rust remover but is a good remover of algae, moss and other vegetable based stuff. Most acids however will remove rust. Maybe try some vinegar to confirm.

Like you I've had problems with float bowls rusting, some actually had pin holes but those had been sitting for a while before I got them. But, all had water in them and actual flaking rust particles. I'm talking stuff from the 60s and 70s.

I am so glad that most small engine makers have begun using plastic tanks! No more rust even if they get water inside.

Older steel tanks would rust in hours if some water got inside but the newer coated ones resist it well.

 

[Steve@Advance]

Yes, the ethanol does absorb moisture. The good thing is the absorbed moisture will still burn good enough to run.

The process disperses the moisture somewhat equally through out the tank, but it doesn't remove it. Trap a small sample (as in the carb bowl) which is ventilated to the outside world, two things happen, more moisture is allowed to enter through condensation, and the ethanol/gasoline mixture evaporates, leaving water and other sticky residue behind.

The water rusts and corrodes, the sticky residue glues the float and needle in place, and coats the surfaces, including the bore of any submerged jets.

 

[caterpillar guy]

The only cure for not having issues with gas engines and carbs is to switch to diesels and then there are still some issues with them if not taken care of like water kept drained out of supply tanks and filters changed along with buying clean fuel and keeping it clean. Just like it used to say on the fill caps of the tractors.

 

[Geo-TH,In]

Back in 1967 I took college chemistry 205 and
206. We were given a sample to run tests to
determine what was in the sample. What chemical
test will determine the difference between zamak
and aluminum?

My bleach test turned the red material to black.

Red is Iron oxide II or Iron oxide III.
Black is iron. Iron is magnetic. I should have
used a magnet to prove it was iron.

I used phosphoric acid on another carb and it
cleaned it off better than bleach.

 

[Geo-TH,In]

I considered galvanic corrosion but that doesn't explain why the iron oxide(rust) was deposited on the plastic float.

Someone needs to invent a carburetor to hold up to today's gas.

Until then, I will drain the carb when not in use and see how long it lasts.

 

[DoubleO7]

20% sodium hydroxide solution. This solution dissolves aluminum(fizzes!). For zinc you can use 2 teaspoons salt/1 teaspoon copper sulphate/1 cup water solution. If object is made of zinc droplet of this solution must make it black.

 

[DoubleO7]

Was that carb the oem carb or a replacement?

Did you determine what the float bowl is made of?

 

[T.R.K.]

Just because you can't see the rusty spot in your tank doesn't mean it is not there. And the rust in your carburetor came from somewhere.

FYI: ethanol DOES like to mix with water much more than it like to mix into gasoline. When it gets enough water in it it completely separates from the gas. the gas floats on top. It is the water that causes the problem. (And ethanol gasoline keeps shops like where I work doing lots of carburetor and fuel system repairs.)