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I’m perusing my owner’s manual lately for being in a slip after years of trailering. I come across this: “Don’t allow your motor to run out of gas, this could harm the engine.” I've always been told to pull the fuel line and a let it run out. I have a Yamaha T50 carbureted 4 stroke. Is it different for fuel injection? Maybe all my friends and neighbors were wrong?

Another interesting read: “When in a slip bring the motor up and use the metal swing bracket to rest the motor on. Then lower the hydraulic lift to keep it out of the goopy sea.” I think that lowering my hydraulic lift when the motor is resting on that swing out bracket would cause it to crush the bracket and keep right on going. ??

Though I have run out my injected Suzuki two times I haven't detected any affect on the hammered needle valves. Perhaps you have to do it as a matter of course in order to induce eventual damage. The engine just seems to quit. A carbed motor dries down past the regulated stoichiometric fuel ratio that it was designed for and misfires to a halt, without noticeable damage. I think the modern materials used these days are pretty resilient and stand up better than the ones we used to run in our 80's muscle cars.

R.

One of the more obvious reasons not to let your gas run out is the same as for a car. The last dregs of gas are thought to be full of all the gunk that settled to the bottom of the tank. You don't want that stuff to get into your engine.

I do not know if that is the reason they suggest it (the wording they use suggests it's more about the motor running dry, not the tank), but there you go.

I was told to not let the gas run out because sometimes the fuel pump will not start back up and you then are stuck trying to re-prime the stupid fuel pump to get the motor going again. I guess if the fuel pump is sucking air it does not pick up the fuel every time on a start.

Several scenarios come to mind; not familiar with this particular motor, but...

Some fuel pumps rely on the fuel for both lubrication and cooling. So the fuel pump might be susceptible to damage, especially if it continues to run. This is a big risk with cars which have a number of fuel pumps, each needing fuel to cool and lubricate them – some would run dry (the "upstream" ones) long before others (the "downstream" ones).

In addition to the “gunk” at the bottom of the fuel tank getting sucked up, there can be phase separated fuel (an ever-present risk with ethanol in gasoline in any engine) at the bottom. This can be a mixture of various proportions of water and ethanol, in with the fuel.

When this gets combusted, it causes the stoichiometric ratio (good one, Ross ) to change, leaning out the mixture, which causes elevated combustion temperatures that can (and often do) lead to engine damage. Running an engine too lean will destroy it in no time, even a 4 stroke. First -hand experience with this here– melts a hole in the top of the piston, among other things.

If you have multiple carburettors (likely on a 50 hp) when you cut off the fuel flow they do not all run out at the same time for various reasons (some are higher, some are below them, and other asymmetries). Again, this would lead to leaning out of some cylinders while others are still running. Might not be for long, but the risk of damage is still there. Of course, a single carburetted engine dies almost immediately when it runs out of fuel.

Then there is the problem you mention BOAT. On startup after running out of fuel you might have some cylinders running lean (BAD!) until full fuel flow is restored.

Note that when fogging for storage you will be flooding with oil at the same time as you are running the last bit of gas out of the carbs, if that is your storage procedure, and so minimizing the possibility of damage.

If I keep thinking about it, I could probably come up with some more, (Einstein said that imagination is more important than knowledge, hah hah ) but hopefully these points will suffice.

- B.

there can be phase separated fuel (an ever-present risk with ethanol in gasoline in any engine)

OK, I'll modify that - AFAIK aviation fuel doesn't have ethanol added, (Hamin X, your input?) because these engines are critically "important".

Other engines are not considered "important" enough, so that makes it OK dump that junk into them.

Not too much bitter sarcasm over here.

Well, with my 4 cyl carb engine, I wonder if "running it out" really does that..or instead, it runs the bowls down to where they can't feed the jets anymore but there is still some gas left in there and due to the smaller volume than the full carbs, this gas can evaporate and turn into gum faster than if you hadn't messed with it at all...well, there is your counter view point anyway

Seriously, I had two bad carb clogs in the early years of 26X ownership (after the P.O. let it sit in an empty lot for at least a year and also pumped a ton of additives through it)..it could have been also contributed to by the introduction of ethanol gas but instead of running the carbs dry, I tend to run my engine at least once a month even if I'm not doing much sailing. AND...probably the smartest thing I did was to install one of those big honking water separating fuel filters about 4-5 years ago. Since then, zilcho fuel problems with anything. And I have replaced the canister once and found a few tablespoons full of water trapped in there so its definitely doing its job and preventing problems. I think water in the gas is a given between being in the marine environment, using ethanol and just the everyday heating/cooling/condensation cycle of the gas.

I think that the main problem with ethanol in avgas is the vapor pressure (I think that is what it's called). It tends to change state at a higher atmospheric pressure (think lower altitude) than gasoline. This could cause vapor-lock. Then there is the problem with older engine seals, fuel lines, etc. Phase separation might be a problem with those aircraft that are not flown often. Besides, it is not FAA approved for part 23 certified aircraft.

~Rich

For the record U should not fogg a EFI engine u'll screw up the intake sensors , u should run the eng with high test gas mixed with fuel stabilizer & some fuel inj. cleaner , some fuel stabilizers have injection cleaner in them already Merc's does I beleive ! remove the spark plugs & spray eng oil into the cylinders crank the eng a few times then re-install the spark plugs . the first time I did not do this in yrs & now I have eng. issues Fuel inj. sticking , even after removing them & having them cleaned & reverse flushed , two of the four inj. started sticking again after only 1 1/2hrs , even ran $80.00 of high test gas with fuel inj. cleaner through her to no avail , so now I'm replacing all 4 fuel inj. @ 160$ a pop , sunk 1 boat buck into her already just in parts me being a tech I'm doing my own labour , Just got tied up that fall with family issues & never gotta done next thing it was winter & too late !
On the other hand I used to run my uzzi 40hp 4stroke dry all the time before winter never had any issues !! so go figure
Cannnot remember if it was central inj or efi single cylinder inj
J

My 75 is a carb 2005 model. Lots of hours on it.
I never run her dry. Every year just run good gas with stabilizer.
Every spring I put the muff's on and she starts up fine... running smooth within a few minutes

I love my merc

it's funny you ask...

After working on outboards for years (mostly OMC, mercs only when I absolutely had to) its funny how things change

in the old day yeah, run her dry to store...fogging oil is good

today Etec, computerized thingamajigs not so much..have heard fogging can damage critical parts on some/most, and seems every one has a different way and a different set of gremlins....

it's amazing to me how robust, yet how fragile these "newer" motors are...and my philosophy is still the same....just more S**t to break, and costly


I still run my 1960 West Bend 16 Golden Shark on occasion....still runs like new...meanwhile I work on some newer models for customers just chock full of issues


Wonder if the optical sensors and ECM on my 1960 West bend need looking at

I've run my suzi dry many times by accident. Fuel line pops off the tank quick connect. It's a PITA to squeeze the bulb to restore fuel, but so far no detectable harm.

I've had the suzuki 140 since 2002 and have run it dry after every time out. I can't always get ethanol - free fuel and I just don't like the thought of that stuff just sitting in my hoses and injectors.

An experienced mechanic told me I was asking for trouble and it shouldn't be done. After I explained I had done it for 10 years, he just said "I stand corrected. Never mind." Who knows?

I do pressure feed it with the fuel line bubble before hitting the starter. Hasn't failed yet. BTW I do keep tanks checked for trash and sometimes siphon/vacuum tbem.

Billy, I did a trip up to Cristal River, FL and say a gas station that only had Reg. Gas (no Ethanol). Surprised me they had that station on a town with 3200 population.
Was on Rt.19 Crystal River.
Only other way to get it is at a marina or delivery min. 50 gals.
Reg. gas last lot longer in fuel tanks with no additives.
When I can't get reg. fuel I add sea foam to fuel or Gas hunk.
Dave

Billy wrote:I've had the suzuki 140 since 2002 and have run it dry after every time out. I can't always get ethanol - free fuel and I just don't like the thought of that stuff just sitting in my hoses and injectors.

An experienced mechanic told me I was asking for trouble and it shouldn't be done. After I explained I had done it for 10 years, he just said "I stand corrected. Never mind." Who knows?

I do pressure feed it with the fuel line bubble before hitting the starter. Hasn't failed yet. BTW I do keep tanks checked for trash and sometimes siphon/vacuum tbem.

Well, I use running my motor dry as the method to determine when I need to switch tanks, so...

There's yet another potential problem with running dry:

When you're starting the motor, the starter is driving a LOT of amps, and heating up. Most cars specifically state that you must not run the starter for more than 15 seconds without letting it rest to let the starter cool down. You can literally melt the solder that connects the starter leads to the motor if you allow the starter to overheat.

I think the ETEC manual says no more than four seconds...

And running dry always involves cranking quite a bit.