Went to use my old Rover with 3.5hp briggs on it today.
It doesn't get used much, the fuel in the tank was admittedly 98 ron bought in early May. I normally have no problems using 98 up to 5 months old (though I don't normally let it sit more than 3-4).
I used it a couple weeks ago and the tank was clean, then refilled with new fuel (a bit dark and didn't look at the state of the tank and ran it 5 minutes). 2 weeks later (today) I take it out and look in the tank and it looked like it was full of milk. Tipped it out and there was a white slime layer through the tank.
Fuel as shown was milky, but no water settled after sitting 20 mins (it is stored in shed that isn't damp). It started with new fuel and when mowing it ran pretty poorly. It was also idling at 2200 rpm - I had it dialed into 1750rpm last mow. Vacujet carb by the way.
I pulled the carby and the white silt in the tank had completely bypassed the pickup filter and clagged up the main jet a bit and the idle nozzle completely.
Filled the tank full of washers and nuts and shook it around - tonne of silt came out.
Now running alright but I have never had this before.
What the hell happened? Checked for ethanol and its pure petrol without alcohol.
Did an old fuel additive caltex put in the may fuel react with the new august fuel?
Hi Tyler, Yep I've seen that happen many times before. Fuel today has a very short shelf life and it turns into all kinds of milky gunk as you describe. I have even seen it turn into something resembling water. I've often had to thoroughly clean up tanks and carbys after allowing fuel to sit for a short time. I have also noticed that silt-like stuff but can't explain it. Perhaps as you say, some kind of additives are unstable and mineralize as the fuel slowly evaporates. It can also turn green as I'm told a special kind of algae can start growing in it.
And another thought just came to mind. Do you have kids? One time a neighbour brought his mower over telling us he couldn't start it. He said it usually started first pull. When we looked in the tank and smelt it, we soon realized what was wrong. The fuel tank had been half filled with water! We told him he must have left it out in the rain. "No" he replied, "always put her in the shed!" We cleaned it all out and put it back together, put some fuel in and away she went, first pull. He took it back, still scratching his head. He comes back a day or two later to tell us his 6 year old son had just told him he wanted to help and had got his sand bucket, filled it with water from the hose, and was about to fill up the mower tank... but this time he caught him in the nick of time. So mystery solved!
No kids vint_mow. What gets me is the mower next to it has the same fuel in it and is fine - maybe its something about the metal tank as the other is plastic.
Never had this problem before with the same brand 98 Ron. I have left a quantum motor 6 months and still ran. Around the 7 month mark the fuel will go off (as in won't fire) but never clogs anything - thats why I use it
Oddly I've noticed the same thing. One tank will be okay, the one next to it has "gone off" and often in a fairly short space of time. I recently purchased a can of fuel and my mowers played up the whole time, spluttering and missing and constantly fouling plugs. As soon as I used that up and refilled the tin at the bowser, I had no further problems. So possibly it is just crook fuel?
I think I might go back and get some fuel at ampol. I had a weird run of machines that I adjusted and needed more turns out on the mixture screw than I would have liked.
I put the ampol in the tanks and within 20 minutes use the were running like crap - running seriously rich. Adjusted the carbs and what would you know, all back to around the factory 1.5 turns out.
I think the fuel cap on the 3.5 Briggs has more breather holes than the plastic quantum tank , so probably allows more evaporation on the 3.5 thus allowing the fuel to break down at a quicker rate.
BP said the following below.
Petrol is a mixture of many components with different properties that contribute to the performance of the fuel. When petrol is kept in an open container where it is exposed to the air, it will - in time - completely evaporate. As it evaporates, the composition and properties will change because different components evaporate at different rates. This is a normal feature of petrol and helps describe the process which takes place when it is stored in equipment fuel tanks.
Petrol in sealed containers
The storage life of petrol is one year when stored under shelter in a sealed container. Once a seal is broken the fuel has a storage life of six months at 20°C or three months at 30°C.
Petrol in equipment tanks
The storage life of petrol in equipment fuel tanks is one month. This can be extended by topping up with one third of fresh fuel, which restores the volatile components that have evaporated. Topping up with fresh fuel will help, however it is not a foolproof strategy for engines that are used only intermittently. The following principles may also help: > Keep the tank half full to stop water vapour from being sucked in and condensing. > Consider using a fuel that contains anti-oxidants, metal deactivators and corrosion inhibitors to protect metal surfaces;
Use a hotter spark plug to help to reduce carbon deposits
Hmm this is why I want a LPG mower , Line Trimmer ,Blower Vac and Quad bike etc.
LPG is not affected by the shelf life issues associated with petrols and diesels. It is stable when stored in sealed containers.
I had a similar issue some time back, I had a large volume of fuel become jellified and was pretty annoyed as it wasn’t cheap so ended up speaking with a petroleum chemist from our supplier.
He told me that the fuel composition is changed between summer and winter months. Apparently they use a mix to ensure the fuel remains liquid in winter and in summer they change it so it doesn’t loose important characteristics through evaporation. He said the mix was gradually changed through the shoulder months.
I don’t know what they do in the warmer parts of the country but perhaps it could just be that it is “summer mix” and you’re experiencing a colder period?
Frosts are not unusual here and our fuel storage was on the south side of a shed shaded by some big stringybarks The bloke told me to fill a container and place it in a warmer position and it would be fine to use once liquid again. Getting it into the jerrycan was a bit of a challenge but he was right, things ran just fine with it too.
Thanks Max, I am really dreading looking at the back of the shed at another 3.5hp briggs that hasn't been used since march (scarifier). It had 1/4 tank in, so will see what its like
Ironbark, I have heard similar.
The other thing I have heard is different volatilities between winter fuel and summer. In summer, the higher heat means lower vapour volatility so as to prevent vapour lock. Winter needs higher vol to aid starting in cold weather.
In the usa back in 2020 at peak covid, due to less driving, there was a glut of winter fuel at the end of season. Apparently its worse with E10, but motors were throwing codes and vapour locking and other general behaviour that EFI largely removed from cars 30+ years ago.
The fuel we had “jellify” looked very similar to what your images show. The first time it happened was on a frosty winter morning and had a bit of comedic value.
The family went out in the car which started and managed to get a kilometre or so down the road and then failed to proceed. Following a phone call I went out in the Landcruiser, to rescue them which got a little further and then similarly conked out. I walked back and we got the smaller tractor out which didn’t even make it to the gate onto the main road.
Three vehicles, all stranded. I went back inside and had cuppa, one of those days.
That sounds a little like the Castle, Ironbark . I need to get the tractor out to get to the Landcruiser then I can get to the car, but I'll have to get the tray truck if I'm gunna move that tractor, just watch that old fuel.
“Ay Steve, can you move the Camira? I need to get the Torana out to get to the Commodore.” “Sure thing Dad, but I'll have to get the keys to the Cortina if I'm gunna move that Camira.” “Alright mate, just watch the boat”
One way to make these old Briggs fool proof is to adapt the later primer plastic carby and fuel tank ,I had a Scott Bonnar 720 here that was sitting with fuel in the tank unused for over 12 months ,I'd previously fitted the plastic primer carby and electronic coil to this 4 hp Briggs and I checked the fuel tank yesterday and most of the fuel had evaporated, just a small amount of jelly looking fuel in the bottom of the tank so I just filled the tank with old 98 fuel gave it a prime and it started 3rd go , then I gave the mower to my Brother to cut his lawn ,the mower worked well, cut well but if it had an alloy carby it definitely would have needed a good clean out.
It felt a bit more Dad and Dave than The Castle at the time. I felt pretty foolish once I worked out what was going on.
I tend to put old fuel into my “cleaning” container and use it for that purpose before the next step which is as a fire starter for the spring and autumn clean ups.
Yep some days are a good example of Murphy's Law , at least you didn't leave old unleaded in a car as long as I have ,on a couple of occasions I've had to throw the fuel tanks out because they were so badly corroded inside but it didn't bother me because I thew the car out with the fuel tank.
I still have about 30 litres of super fuel must be at least 20 years old ,last time I tested a small amount it was still flammable , it would be interesting to see if a mower would run on this old fuel.
