Boat Sputters after I turn it off
 

I went out of town with the boat this weekend and filled up at a Sinclair. A few times when I would shut the engine off it would sputter a little bit before it actually shut down. Doesn't happen every time and I was wondering could this be the gas I filled up with or is there something I can put in the clean it out?

Jeff

Re: Boat Sputters after I turn it off
 

Unfortunately, this is somewhat common on the 3.0 liter 4 cylinder engines, less common on the 4.3 V6, and even less on the V8's. What engine do you have?

I've heard a few things that I'll relay here - this is called dieseling. It is usually due to engine heat that causes the gasoline to ignite even without a spark. I've heard if people run their bilge blower constantly and don't shut off immediately after running fairly hard, that this can be reduced or eliminated.

Somehow, you need to get that heat out. Is your cooling system working properly (fairly new impeller, etc)? Try running the blower more. I've also heard some say a higher octane fuel will help. It requires more heat to ignite, but that gets expensive.

Re: Boat Sputters after I turn it off
 

I have a shabah 212Z with the V8 engine.

Re: Boat Sputters after I turn it off
 

As indykoch noted: This is referred-to as "dieseling" or "run-on." There are two typical culprits:

• Octane of gasoline too low. Ethanol blends are particularly problematical.
• (Spark) timing advanced too far

That latter one may need some explanation, because one's first reaction tends to be "Why should that matter? The ignition's off." But timing advanced too far causes the engine to run hotter than normal.

First try upping the octane rating of the gasoline you're using. I never buy the lowest-octane fuel for our MerCruiser 4.3L V6. Also recommend you treat your gasoline with Stabil Marine Formula.

Jim

Re: Boat Sputters after I turn it off
 

I have been using the Unleaded 85 but will bump it up bnext time I am out and I will also mix in a bottle of the Stabil

Re: Boat Sputters after I turn it off
 

That could very well be the problem - Mercruiser recommends 87 octane. I don't know that I've even seen 85! Where are you located?

Re: Boat Sputters after I turn it off
 

Colorado.

I will try the 87 next time and hopefully it fixes the problem.

Re: Boat Sputters after I turn it off
 

Make sure to get the Marine Formulation. Also you won't mix in an entire bottle. For in-season use, it's only 1 oz. per five gallons of gasoline. I bought the biggest bottle of the stuff they had so it would last a few seasons.

Jim

Re: Boat Sputters after I turn it off
 

Letting it idle for a few seconds before shutting it off should help too.

Re: Boat Sputters after I turn it off
 

I'm on board with everyone that posted. Octane is more important than most think,, It allows a cooler more controlled burn in the cylinder. when the combustion gets hot some edges of parts in the cylinder glow creating the engine to run every time the piston sucks in air/fuel mixture and even though the plug doesnt fire the hot spot will ignite it. Also, make sure the idle is not too high, that can cause the engine to take a few more revs to stop. Good luck,, gremlins on my side are stumping me with my girl. :wink_thumbup:

Re: Boat Sputters after I turn it off
 

Btw: Almost forgot: A lean fuel mixture can also cause an engine to run overly-hot, and result in dieseling.

Jim

Re: Boat Sputters after I turn it off
 

I've also noticed engines do it if the idle is set high to compensate for a lean condition to prevent stalling when you shift into gear.
I use Marvels Mystery Oil to help with the low octane gas in our area, seems to help quite a bit. I only use Stabil in the winter, but it couldn't hurt.

Re: Boat Sputters after I turn it off
 

I second the use of the Marvel Mystery Oil -- worked well in my Toyota Avalon with 270K miles, too.

My store was out of it recently and the guy at the marina put K100 into my fill-up. Has anyone had experience with that product, good or bad?

Re: Boat Sputters after I turn it off
 

So I changed out all 8 plugs, switched to 87 octane and poured in so combustion cleaner and it ran great until the end of the afternoon and it happened again.

I am in Colorado so 5500 elevation.

I noticed it seems to happen after pulling the tubes at a slower pace for a while.

I will try adjusting the idle a bit!

Marvel Mystery Oil is that something that goes in the gas tank or a type of oil when I change it?
Can you find it at the auto parts or marine?

Thanks Guys.

Re: Boat Sputters after I turn it off
 

Marvels is a detergent that can be used in the gas to replace lead & improve octane and can be added to oil to free lifters & clean the crankcase. It's sold in auto parts stores and most department stores.

How fast is your boat idling and what is the engine temperature when it does this? if allowed to continue it can damage the engine.

Re: Boat Sputters after I turn it off
 

I usually use the simple solutions.

1. Try higher octane gas.
2. Let the engine idle for a minute to pump cool water though after running at speed.
3. Shut if off in gear.

Re: Boat Sputters after I turn it off
 

When we are running full open it runs about 150 for temp. I am not sure what it idles at Ill check next weekend.

What should it idle at?

It ran a little better yesterday but but I didn't pull anyone at slow speed for an extended time.

Re: Boat Sputters after I turn it off
 

Just a thought, check your timing.

Re: Boat Sputters after I turn it off
 

How do you check the timing?

Is this the plug gap?

Re: Boat Sputters after I turn it off
 

I changed the plugs like I mentioned and added some combustion cleaner and upped the octane but I am not through that entire tank yet.

Could it take a few tanks of the cleaner and the higher octane before I notice anything.

Re: Boat Sputters after I turn it off
 

I'm having the same issue with sputters when turning the engine off, I also noticed that my speedometer stopped working and then started to work again??? any ideas on the speedometer, on the Sputters I'm going to try higher oct. gas, I have half a tank now should I re-fill with higher oct. now or wait for the tank to be empty? or close to it?:shakehead::shakehead:

Re: Boat Sputters after I turn it off
 

I tried higher octane and it didn't make a difference so I settled on 87. I never put in 85.
I all added a few bottle of different additives to help clean things out. Like sea foam, Lucas oil over time. I also changed the plugs a few years ago and whatever the combo this year it has helped.
Good luck

S if you are using an 85 octane go ahead and mix it with a higher but if you are already using an 87 in think you are probably ok.

Re: Boat Sputters after I turn it off
 

jorge: this thread is a couple of years old but if you do a site search for 'speedometer' or 'speedo' you will find numerous threads on that problem. For starters though i will suggest that it is likely the pickup hole in the front of the outdrive that became blocked and then cleared itself that caused your problem with the speedometer.

Re: Boat Sputters after I turn it off
 

CHECK YOUR TIMING FIRST!! I had the same problem with my 5.0LX and ended up spending a lot on parts I didn't need when I could have fixed the problem by retarding my timing back to the correct 8 degrees BTDC. Checking the timing will require a timing light. You can buy one for $40 or borrow one from a friend. I'm not positive on the correct idle timing setting for your boat but I'm guessing it's around 8 degrees BTDC (before top dead center). Let me know if you have any other questions.

Mike

Re: Boat Sputters after I turn it off
 

I had a 1996 Shabah with a 4.3 merc Alpha 1 outdrive. I had the dieseling problem too until a boat mechanic had me go up to 91 Octane. Never had a problem after that.

Re: Boat Sputters after I turn it off
 

Although timing is a likely cause, it can also be caused by "coked" pistons (caused by running too rich) but in my case it was early signs of leaky exhaust manifolds. A very small amount of water was getting into the exhaust which would be blown straight out when the engine was running, but as soon as the engine was turned off the water got into the pistons and caused run-on. I didnt realise this at the time and the eventual result was hydro-lock and a broken starter motor! New manifolds sorted the problem.:wink_thumbup:

Re: Boat Sputters after I turn it off
 

I have a 3.0 Mercruiser on my '03 SX8. I experienced the same thing. I started running high octane and it made a difference.

Re: Boat Sputters after I turn it off
 

My Z212's V8 does this sometimes after a hard ride or pulling skiers. I fixed it buy either letting it idle down a few seconds, and tossing in a bit of Sunoco 112 race fuel that I run in my motocross bike. Plus one gallon makes the thing smell great for a solid month :) I also run nothing but 93 with no ethanol. Thinking about switching to just racefuel next year.