I have a 4-stroke outboard engine – I do NOT want a 4-stroke outboard.
So why do I have a 4-stroke?
In 2005, in Panama, I bought a new (tax-free) 15hp Yamaha Enduro outboard. It was a 2-stroke machine; powerful, reliable, easy to DIY-service (could have been salvaged even in the event of being submerged) – and easy to start. I loved it.
The Yamaha was stolen less than a year later in Raiatea, French Poynesia. The only replacement outboard of the required size (15-20hp) we could find in the Society Island was a 4-stroke Suzuki, which was shipped to us in Raiatea from Papeeté. I didn’t really want a 4-stroke outboard on a cruising boat in the third world; it is heavy, technically complex and vulnerable. But I had no choice. As with everything else in Polynésie française it came with a price: more than double what I had paid for the Yamaha. In addition to the price of the engine itself, I later had to design and order a hoisting crane on the transom because of the weight of the machine.
Our biggest problem with the outboard has to do with the increasing mix of ethanol and other (“bio”) ingredients in gasoline. At the filling station pumps we cannot get 100% gasoline (or even something like E5 98 octane) anymore (at least not where we have been in Malaysia and Thailand). Markus, who runs the Suzuki service at Derani Yachts in Boat Lagoon told me that one of his customers had sent a sample of the local 95 octane fuel to a laboratory and found out that there was 20% ethanol and 10% palm oil!
The primary reason for ethanol (ethanol alcohol) being harmful to an engine is alcohol’s water-absorbing and solvent qualities. Ethanol is an excellent solvent. It will dissolve plastic, rubber, some types of fibreglass and (I think) even aluminium. It will create a sludge that coats and travels through the engine, causing complications including clogged fuel filters and carburetor jets. Therefore all major car and marine motor manufacturers have limited the allowable portion of ethanol to 10% (in the western world this fuel is called E10 and is 95 octanes). However, when even ten percent is questionable, imagine what higher levels of ethanol can cause. Regarding the 4-stroke outboard the biggest problem is the complex (and expensive) carburetor. Fuel flow is adjusted by extremely tiny orifices (referred to as jets) in the body of the carburator. The sludge created by ethanol will definitely clog these jets. With the extremely simply carburetors of 2-stroke outboards this is less of a problem.
I have found out (the hard way) that if the engine is run every day there is less risk of a clogged carburator, but if you leave the outboard standing for more than 2 days it is best to completely drain the carburator. This is done by opening a screw on the side of the device and letting the fuel out. This is a messy operation and can not be done after you have hoisted the outboard up on deck, so before hauling it out you need to know when it will be in use next time. There is no practical way to collect the drained fuel either, so guess where it ends up? And the idea with 4-strokes was supposed to be their environment-friendly clean burning process (due to precise fuel injection) ….
And before you suggest just disconnecting the hose to the fuel tank and then run the engine until it is out of fuel: don’t! It doesn’t work; I don’t know why, but I have tried.
So, why is this not a problem with cars? There must be millions of cars running on this ethanol-rich gasoline day after day. The reason, I am told, is that they have high pressure fuel injectors, which is also the case with bigger outboards (over 40hp).
An other problematic quality is the short shelf life of fuel containing ethanol. Even E10 is reported to have a shelf life of only 1-2 months in ideal conditions. Fuel in small boats is usually stored in jugs prone to condensation and consequently some water builds up. Therefore, with higher quantities of ethanol, we shouldn’t store more than a couple of weeks use of outboard fuel onboard – particularly in tropical conditions. Problem is that some times there will be months between the filling stations.
4-stroke outboards are great at your summer cottage in the western world, where you can better trust the quality of the fuel at the pumps and don’t have to store any reserve amounts at home – and, where you can easily contact a repair work-shop when shit hits the fan.
Related article: From Polynesia to Cook Islands.
