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I'm having issues suspicions with the Exmark and other brands that use plastic gas tank. Specifically, my Exmark is an '07 and lately I've been having issues with gasoline flow to the carburetor. I modified my fuel system by changing the fuel line and adding tees along with shut-off valves and a dual parallel filter design. I'm experiencing water in the tanks and what appears a milky looking sludge that keeps plugging the filters and now plugging the carb's idle jet causing engine rpm surging at idle. Since the mower is 12 years old, I wonder if the inside of the gas tanks are starting to deteriorate and causing the milky sludge? Do these have an inner coating that can disintegrate and cause this milky sludge? Since day one, I have only used ethanol-free gas and have added Sta-Bil along with Marvel and other additives to my tanks. I wonder if the inside of the tanks are now breaking down?

I have never seen the inside of the plastic tanks deteriorate like that, crack and get brittle yes but no leach. I suspect that you are picking up a mixture of ethanol, water, and the resulting bacteria that grows in that alcohol, dirt, water mixture. It can have the appearance of snot. The other think could be that the aluminum carb is corroding and you are getting aluminum oxide which is a white powdery substance that can look like a grey/white sludge.

White milky look means water...
If the gas was dissolving the plastic, then you would have baked crystallized plastic locking up the engine, which is what happens when folks use things like milkjugs to transport their fuel.

Probably just water from condensation. Is the mower stored in an area where the temperature fluctuates significantly?

Old E10 fuel does this .
The ethanol settles out then adsorbs moisture from the air overnight.

Boit4852 said:

Since day one, I have only used ethanol-free gas and have added Sta-Bil along with Marvel and other additives to my tanks. I wonder if the inside of the tanks are now breaking down?

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Sounds like we may be able to rule out E-10, but I test my gas. This is what water in E-10 looks like, & how it separates.

ILENGINE said:

I have never seen the inside of the plastic tanks deteriorate like that, crack and get brittle yes but no leach. I suspect that you are picking up a mixture of ethanol, water, and the resulting bacteria that grows in that alcohol, dirt, water mixture. It can have the appearance of snot. The other think could be that the aluminum carb is corroding and you are getting aluminum oxide which is a white powdery substance that can look like a grey/white sludge.

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I've been draining quite a lot of water from the tanks lately. Two years ago, I replaced all fuel lines and ran separate lines form each tank along with a valve to shut off flow from each tank so that I can drain a few ounces from one tank at a time. I ran each line down to it's own 11 micron filter and then to a common drain just downstream where I had teed the filter outlets together. I also eliminated both check valves as I view those as unneeded restrictions. Today I loosened the float bowl solenoid and caught what came out of the bowl and found it was mostly water. I think the water is accumulating in the tanks because I haven't used best practices in the colder months and not keeping the tanks full to minimize a large air space which pulls in outside air/humidity during thermal cycles. I have no place to store the machine protected from the huge swings in temperature so I park it a concrete slab and keep it covered with an ATV cover. Today, I pulled off the fuel bowl off to see what was in it and clean it out. Unfortunately, the o-ring dropped out the sealing groove and I can't get it stay in place when I reinstall the bowl.I'm going to remove the carb and clean the jets and get that o-ring back in place. From now on, I'll keep the tanks full after mowing to eliminate the air space. I've on ever used E-O gas plus I add Sta-Bil and Lucas ethanl treatment. I hope the dealer where I buy my E-O gas is not selling E-10 as E-O then charging the higher price.

7394 said:

Sounds like we may be able to rule out E-10, but I test my gas. This is what water in E-10 looks like, & how it separates.

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I've been wanting to get an ethanol tester so now you've convinced that it would be a prudent thing to do. Thanks.

Test his gas, it's simple. You can google it & get lots of pics with it I'm sure.

As to your 0-ring, try wiping it with some grease (thinly) to help it adhere to the carb, while you put the bowl back up. .

Boit4852 said:

I've been wanting to get an ethanol tester so now you've convinced that it would be a prudent thing to do. Thanks.

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Don't buy one, make one. It's simple. Like I said google a decent you tube on the subject.

Darryl G said:

Probably just water from condensation. Is the mower stored in an area where the temperature fluctuates significantly?

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Yes. I wish I had a better place to store it. I DO keep an ATV cover on it at all times but that's no protection from the high temperature fluctuations. I think keeping the gas tanks full will help to some degree with allowing humid air from being sucked into the tanks when they have a large air space.

Seafoam is what I like best. But everyone has their own preference.

ILENGINE said:

I have never seen the inside of the plastic tanks deteriorate like that, crack and get brittle yes but no leach. I suspect that you are picking up a mixture of ethanol, water, and the resulting bacteria that grows in that alcohol, dirt, water mixture. It can have the appearance of snot. The other think could be that the aluminum carb is corroding and you are getting aluminum oxide which is a white powdery substance that can look like a grey/white sludge.

Click to expand...

Ilengine; I don't know for sure that the inside of my tanks are breaking down. Just a possibility that occurred to me. Since the mower is an '07, I thought that age may be wreaking havoc on the plastic. I don't know if there is a special coating on the inside or not. I DO know that fuel vapors do leach through plastic tanks over time. My tanks have discolored severely over time from being the light gray color to a much darker gray/brown color that is worse at the bottom and gets gradually lighter gray as it gets closer to the top. At 12 years old, I suppose this is a normal result. Just the way it is and I'll jet have to continue working with it and try to minimize it by keeping the tanks full.

7394 said:

Seafoam is what I like best. But everyone has their own preference.

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Sea Foam is in my arsenal as well. I just checked my inventory and I have 11 cans left. Time to hit Wallyworld.

Tanks are made from HDPE ( High Density Polly Ethylene ) it is the only material that they are allowed to be made from for quite some time.
Like all plastics, HDPE is not fully stabe.
Like every material on the planet HDPE is not immune to the effect of UV rays.
Sunlight will eventually cause the plasticizers to oxadize and the tank will become brittle and start to go chalky on the outside.
On the inside they should be stable till the UV damage penetrates full depth.

I suspect what you are seeing is "Phase separation".
This happens because ethanol is not soluable in petrol and much like the old days of mixing engine oil with petrol to make 2 stroke fuel, eventually the ethanol separates out.
Ethanol also adsorbs water and when it does this it becomes heavier than the petrol so it sinks to the bottom of the tank.
The final stage is a bacterial growth in the water / ethanol mix and the dead bodies & excertia from the bacteria makes a jelly like substance.

It is very similar to the fungus that grows in diesel and the alge that grows in Jet A1

Boit4852 said:

Yes. I wish I had a better place to store it. I DO keep an ATV cover on it at all times but that's no protection from the high temperature fluctuations. I think keeping the gas tanks full will help to some degree with allowing humid air from being sucked into the tanks when they have a large air space.

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Yes, it should help both to minimize internal condensation and to preserve the gas better during storage by reducing volatilization of the volatile components of the gas.

Edit:. BTW one of my machines is the same as yours, a 2003 Lazer Z HP. It's stored in an unheated shed and I've never had issues with water in the fuel storing it with the tanks filled to nearly the bottom of the filler neck. And that's with E10 gasoline.

I have an ‘04
No issues with the tank material breaking down. No water issues, I do use sea foam

If you have water issues in fuel, you are getting it from the gas station.

Change the brand of gas you are using.

100% real gas is best.