Engine run-on with 3.0L Mercruser I/O normal?

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  #1  
Old 07-06-04, 07:43 AM
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Question Engine run-on with 3.0L Mercruser I/O normal?

I was told that Merc engines alway have a problem running on when you turn it off without letting it idle for a while. That is a real pain when you try to get a swimmer back into the boat! I have to tell the kids to tread water for a while to let the engine idle befor I turn it off!! Also does this run on hurt the engine? I end up letting the engine 'chug' while the kids are getting back into the boat ( the ladder being beside the engine.)

It is also a pain that the engine dies when you go from idle to full open. ( trying to pull a skier). I have to advance the trottle slowly.

I know someone else who has the same boat ( different year) and has the same issues. Its a 2002, 1950 Classic bayliner.

I was told that all Mercs do that, and there is nothing to be done about it, should have bought something else!. The dealer said its the Ethonal gas.

Is that true?
 
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Old 07-06-04, 07:03 PM
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I just read your problem on the other thread

I see what you mean about run-on.I dont know much about Mercs but I'd be willing to bet thats not entirely true.Most the guys that I know run Mercruisers and they seem to run fine.I'm not to sure about the fuel you run,but maybe I can help you with more info.I happen to work in the operations department of an oil refinery.I'll check with someone in the lab who might be able to explain why this might be your problem and what you can do about it.
 
  #3  
Old 07-07-04, 08:38 AM
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Thanks, called dealer again, still said its the gas

They suggest I use the high octain. that all Mercs do that. (Funny, since they sell mercs)

But another mercury marina ( there are not many out here) said the carb/ timing is not right. but they do not handle bayliners, the adjustment would not be covered under the warrenty. ( It did this since day one).
 
  #4  
Old 07-08-04, 06:19 AM
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what grade octane are u using? most marine engines require at least an 89 octane. also, at what temperature is the engine running? look at the temp gauge. a hot running engine will often times run on when it is shut down. when u put it in idle for a couple minutes or so the engine has a chance to cool off, hence it will not run on. find yourself another mechanic. run on is not normal, i don't care if it's a merc or not. and all merc don't behave this way. i suggest u get it taken care of, as this can cause engine damage.
 
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Old 07-08-04, 08:05 AM
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Hello; CanadianInIowa

I fully agree with all prior advice offered. Engine run on is not normal and is not usual or related to engine brand, etc. But there are causes.

Some of the possible or potential causes listed below:
Excessively high idle speed.
Moderately high idle speed or any incorrect idle speed above OEM specs.
Excessively rich fuel mixture.
Engine temp.
Engine timing.
Excessive carbon deposits in the cyclinders or on the valves, etc.
In correct fuel type or fuel octane rating, etc.
Incorrect spark plug type...too hot or fuel deposits on the electrodes, etc.

All causes and or conditions must be fixed and or corrected asap. Run on is detonation. May cause engine to run backwards. Pounds the crankshaft bearings and will cause major engine damage to any and or all internal parts.

Temp solution only. Turn engine off while in gear. The load often shuts down and or stops engine run on. Not always or a perfect solution. Only a temp solution and not a fix.

Until you can find a real mechanic whom is capable of fixing the condition and not make excusses or pass the blame onto the brand name do to his/her lack of knowledge on how to correct that condition.

The diy resident boat service & repair professionals will have additional helpful information, suggestions and advice. Check back on your question several times for additional replies.

Diy boat mechanics, at this bussiest time of the year are swamped with work and may not be able to post replies for some time. Not an excuse but a known fact.

Kindly use the reply button to add any additional information or questions, etc. to this thread. Using this method also moves the topic back up to the top of the daily list automatically.

Regards, Good Luck & Safe Boating.
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  #6  
Old 07-08-04, 10:13 AM
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i agree with the above poster, except the advice to turn off the engine in gear. doing so can suck water backwards up thru the manifold{s} into the pistons etc. causing major engine damage. i've heard of it happening. don't do it!
 
  #7  
Old 07-09-04, 09:26 AM
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Angry Called Mercury - says nothing to be done!

I will pay another marina to see what can be done (Not a mercury dealer). I started buying the Gas at the one marina on my lake (Still does it). Called Mercury and they say that this is normal for carberator marine engines to do that and it does not hurt the motor, a friend suggested running the blower to see if I can cool the compartment air. I guess All I can do is pay another person to look at it. ( Even though it was doing this since day one). the boat is only one year old!

Ill let you know the outcome!
 
  #8  
Old 07-09-04, 12:42 PM
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Sorry It took so long to get back.I talked to someone about your problem and he said your type of fuel should not be the problem.After talking with others (Boat owners) about your problem I have come up with some questions they would have asked you.First check your spark plugs.That will tell you a lot of info on how your carb is working.Notice if they are really black.That would be most likely a sign of running too rich.Also try a higher octane fuel,maybe one with some type of anti-knock detergent.Many of the larger gas companies sell fuel with additives.
 
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Old 08-11-04, 06:33 AM
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updat on run-on - took in to marina

I took it into another marina and had them adjust the timing and reduce the idle. It still will 'chug' when turned off right away. but not as bad as before.

But it does appear that I have lost the power that I once had!, they re-adjusted the timing, and it is back to before plenty of power- I do think there is nothing to be done about it. they say it will not hurt the engine - just get use to letting it idle befor turning it off. Atleast it did not cost me much - and I got my speedometer to work again!

Thanks all for your advice.
 
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