Ethanol

[Matt]

Generally speaking, I reckon it's all OK. But yesterday I saw evidence otherwise.

One of aux motors is a 2000 Johnson 5hp (a rebadged suzuki). Lovely little motor, albeit single cylinder rather than the twins they used to do.

Anyway, hardly been used in it's entire life - it had done maybe a couple of years service, then had a gearbox problem and was put away in he garage for for a number of years.

I recommissioned it in spring 2019, which included rebuilding the gearbox and a new cap for the tank. The new cap also comes with a bit of foam to help stop fuel from splashing out the top.

The tank had 97 octane in it from BP Winchester, along with Quicksilver lube @ 50:1 (Yeah, I know the motor can handle 100:1). Have been running the motor every few months in the tank just to keep it "active".

Anyway, lifted the fuel tank cap off yesterday and the foamy bit in the cap had completely disintegrated into mush which was perfect to block a small fuel filter!!!

Tanks now drained and completely dry on both my aux outboards.

On the flip side, the fuel in my boat's main tank is 2 years old (the same BP 97 octane stuff from winchester) - and I've recently drained a hundred litres out which is burning through the landrover and the MG - all seems fine.

So anyway - message is - keep an eye out on your older aux outboards, especially if the cap has a foamy bit (you can just see it under the silver disc below) in it to stop splashing.

[jeffstevens763@g]

Use aspen fuel for them lasts five years

[Matt]

Yes, that's what I'll be switching the small motors to.

[TmMorris]

Yup. Good fuel management and common sense will negate water issues but with older outboards we need to be careful re the plastics.

As Steve says, albeit expensive, the easiest solution for old, small outboards that get little use is to use garden centre petrol and just carry on as of its 1985.

[jwalker]

Matt, do you have evidence it was the alcohol that did it? Foam often disintegrates with time. I've a similar piece of foam on the cap of my wee Honda outboard, well, I used to have, it's pretty much gone so I just removed it all.

[Matt]

Good question jw. The reason for my suspicion is that the cap was new in 2019 and it’s only had 2 tanks of 97 octane with 5% ethanol in it. So actually, maybe it wasn’t the 5% ethanol - but if not, why would it have disintegrated so rapidly and so completely?

Anyway, had already decided these motors can have the aspen since they’re rarely used.

[TmMorris]

I've also just noticed that it's a 2000 model. Ethanol was being used in quite a few markets by then so global selling outboards would be using plastics by then that weren't impacted by ethanol.

Ethanol has been in some South American markets for decades, in the US since the 90s and used in Asia along with anything else that can burn for decades.

I'd be wary with an 80s engine in case they used different materials in different markets. I'd even be cautious with a 90s motor but I would be surprised if a 2000 motor wasn't made to be compatible but you never know.

[jeffstevens763@g]

Aspen sold in two stroke and four stroke for info about £20/5 Ltrs

[Matt]

Originally Posted by TmMorris

I've also just noticed that it's a 2000 model. Ethanol was being used in quite a few markets by then so global selling outboards would be using plastics by then that weren't impacted by ethanol.

Ethanol has been in some South American markets for decades, in the US since the 90s and used in Asia along with anything else that can burn for decades.

I'd be wary with an 80s engine in case they used different materials in different markets. I'd even be cautious with a 90s motor but I would be surprised if a 2000 motor wasn't made to be compatible but you never know.

Not just a 2000 motor - but also a cap that I bought new in 2019. Although might well have been sitting on the shelf for a few years I guess.

Anyway, it is what it is - and as jw notes, I am speculating a bit that it was the alcohol that did it - either way, I recommend people to check their fuel tank caps at least.

The other thing I notice these days is white crud on the tank internals. Had to take the sensor out of the big boat's tank at the weekend - again, it's only been in a couple of years - and all the metal on it had white crystalline crud on it. I am sure I don't remember that "back in the day"?

[TmMorris]

Of you were to find white gloop in a tank then the most likely cause today would tend to be ethanol emulsion. I'm not sure if that would then be able to crystallise.

Integral fuel tanks are a risk point for ethanol emulsion but its going to be quite usage sensitive. To get an emulsion to form in normal heat and pressure environments you're going to need several months and quite a bit of excess water.

Ethanol, being hydroscopic will actually take up the small amounts of water caused by a tank sweating in normal use and allow it to simply go through the engine unhindered. It actually keeps the tank dry and stops water build up but if a tank already has quite a bit of water in it, or water is finding its way in beyond just the atmosphere and then that fuel is left sitting for quite a while then the ethanol can take up enough water to drop out of solution as a white emulsion.

A boat that is used frequently, has a clean tank and no means for rain or seawater to get in would be hard pressed to have issues. Going forward though, people with boats with internal tanks probably ought to get into the habit of flushing them at the end or start of the season and ensuring water can't get in, especially if an infrequent user.

[Matt]

My boat lives dry & under cover all year except when in use. Even has heaters in (not in the tank!) over the winter to prevent condensation, so happy with that side. But my new SOP will be to cycle leftover fuel out of it and through the cars I think.

Originally Posted by TmMorris

...boats with internal tanks probably ought to get into the habit of flushing them at the end or start of the season and ensuring water can't get in, especially if an infrequent user.