This has happened twice when filling up the 1991 560SEL. I normally use the HEET product to break up the water; does anyone know any way of testing the gasoline for water PRIOR to fueling up the car? Also, does water in the gasoline require changing the fuel filter(s)??

We had that problem with a station in Carson City. Word got around to not buy there. That place no longer sells gas. I don't know of any other field tests except maybe pumping a sample into a clear container and letting it sit to see if water collects at the bottom.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Thank you for the advice. Perhaps there is room for someone to develop and create an at the pump test for water. These engines are not made to run on water and the potential for damage is of concern. For the price per gallon they charge, one would think they would guarantee water free gasoline.

How do you know that water is in the fuel?

Test methods for water in fuel

Test Methods for Water in VO | Quality Testing

a carbide manometer would work on gasoline, some of the other methods would not work obviously.

Doesn't the 10% ethanol that makes up most gasoline combine with the water and keep the water suspended in solution? Where I live all gas, regardless of brand, has some additive or another to absorb water. It comes that way right from the refinery.

__________________
Resistance is Futile.

Yep, built in " dry gas ".

The test for alcohol in gasoline is to draw a fuel sample in to graduated cylinder, note volume, add a measured volume of water, shake then read the amount of water that does not mix. ( It will remain on the bottom. ) The higher alcohol content, the less free water in the cylinder. A chart exists to convert the water volume to % alcohol.

The car misses and acts like it is going to die at idle. Once I give it some throttle, problem disappears. Fuel filter replacement is in the car's immediate future, in the meantime I am going to try Gumout complete to try and remedy the problem.

The gas station has a paste that they smear on the end of their measuring stick for checking tank levels that changes color with water. The water sits at the bottom of the tank, and shouldn't be allowed to exceed a certain level, where the suction inlet is. You can ask them, or wait until the fill truck comes by.

__________________
Prost!

Have you tried fueling at other stations to see if the issue goes away?

If it happens consistently, missing could be an ignition problem.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I was in the not so good part of town yesterday and needed fuel. Stopped at a convenience store to take on a small amount of fuel to get me to my main ethanol free pure gasoline station. Unfortunately the convenience store advertised "may contain up to 10% ethanol" at the pump. I put only a few dollars worth to get me to my main station which sells pure gasoline (no ethanol). Filled up the rest of the tank and went to lunch. After lunch, started the car and that is when the missing and gagging began. Immediately revved the engine slightly so that it wouldn't die. When I arrived home, the car seemed to idle down fine. So, we'll see how it runs today, but I do know the fuel filter needs changing and I'm going to add Gumout complete to the fuel system.

I think the bad gas may have come from the convenience store, but I have no proof. The car was not missing and idled smoothly prior to yesterday's gas mishap.

when I was manager at a gas station years ago we had a paste to rub on the gallons stick that would turn a color if water was present.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

It does sound like bad gas. It may not be water in the fuel. Old gas will do funny things as well. If the station doesn't do much volume the fuel could have gotten a bit aged. Modern gasoline goes bad a lot faster than the old stuff did. I would probably just run it down some and then fill with good gas.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

You still don't know for sure if you have new water each time you added fuel.

The 10%ethanol content in gasoline is a Federal law, it is unlikely your regular station is selling non road legal fuel. ( unless there is some sort of work around I don't know about. )

According to your past posts, I count 3 fuel stops you attribute to bad fuel, it is pretty unlikely that 3 different stations all had "bad" fuel.

A clogged fuel filter won't cause an idling problem unless it is so clogged that the car won't go faster than 10 MPH. Faster speeds = more fuel flow through the filter, if it flows enough fuel to move the car it will flow enough for idle speeds.

Don't guess at problems, diagnose.

Here in Canada most premium grade gasoline has no ethanol, mid grade a little, and regular contains a lot by comparison. The ethanol requirement is an across-the-board average, so they get their average required percent by doping the regular.

A simple 'shake-up' test with gasoline in a tall glass container with an inch of water in the bottom will let you calculate the alcohol percent.