What causes fuel dilution in an EFI/TBI boat?

[garycinn]

I did an oil analysis on my Merc 25W40 oil after 53 hours and it showed a very high fuel ratio (6.8%). See http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=001855#000000 for more details.<br /><br />What could cause this? The boat cranks a couple of revs and fires right up. Anytime I need to turn on the ignition w/o starting it (to look at gauges), I turn off the kill lanyard so fuel not sprayed into the intake.<br /><br />Can an EFI/TBI go bad? Is it from running WOT too much causing a rich mixture? Can the dealer do something by looking at computer diagnostics and tuning it better? It runs great with good fuel economy. It is used for lots of water sports (lots of starts & stops). Should I just not worry about it because it is the nature of the beast and change the oil more frequently?<br /><br />Engine is a 2001 Merc 4.3L V6 TBI w/ Alpha I. Oil was put in November 2003 and drained July 2003.<br /><br />Thanks for any insight.

 

[ron7000]

Re: What causes fuel dilution in an EFI/TBI boat?

my '02 bayliner with the 3.0L is the same way. I had around 4% fuel dilution when I did an oil analysis last november on redline 10w40, and is available over there. Mine's carb with mechanical fuel pump. I run mine the same way, waterskiing. It runs great, if anything mine runs lean- plugs are white with no soot on them at all. Only ideas I could come up with was the mechanical fuel pump seaping fuel into the crankcase. But you have an electric fuel pump, correct? Other than that I don't know what to tell you. The diesel rated oils- mobil delvac & chevron delo 15w-40's would be better suited to handling fuel dilution than the merc 25w-40.

 

[Wart T]

Re: What causes fuel dilution in an EFI/TBI boat?

Change oil more often.

 

[garycinn]

Re: What causes fuel dilution in an EFI/TBI boat?

Thanks guys. Yes, I have an electric FP.

 

[DHPMARINE]

Re: What causes fuel dilution in an EFI/TBI boat?

actually an interesting topic.I am assuming this dilution is mixed with the oil.5% of 5 qts. is what ......8 oz.Certainly if this was h2o it is not acceptable.What is acceptable % for oil/gas in the crankcase?<br />DHP

 

[Dunaruna]

Re: What causes fuel dilution in an EFI/TBI boat?

Does the oil analysis refer to raw fuel or hydrocarbons?<br /><br />Aldo

 

[garycinn]

Re: What causes fuel dilution in an EFI/TBI boat?

DHP, The high end of not acceptable / showing problems is ~2% I believe.<br /><br />Dunaruna, I'm not sure. I think raw.

 

[DHPMARINE]

Re: What causes fuel dilution in an EFI/TBI boat?

2% would be about 3 ounces to 5 quarts of oil.<br /><br />Not a problem.<br /><br />are we talking alcohol content in fuel?<br /><br />DHP

 

[garycinn]

Re: What causes fuel dilution in an EFI/TBI boat?

Originally posted by DHPMARINE:<br /> 2% would be about 3 ounces to 5 quarts of oil.<br /><br />Not a problem.<br /><br />are we talking alcohol content in fuel?<br /><br />DHP

But I was close to 7% <br /><br />I always use Shell regular or Marathon gas in my boat to minimize the risk of getting any alcohol or ethanol.

 

[seahorse5]

Re: What causes fuel dilution in an EFI/TBI boat?

I've had oil analysis done on Yamaha 4-stroke outboards and that has shown from 3% to 7% depending on how much trolling was done. This is what remained in the oil after a long run back to shore.

 

[cobra 3.0]

Re: What causes fuel dilution in an EFI/TBI boat?

All I can think of is with marine engines running richer, these levels are normal. Changing oil every 50 hours may be more appropriate.<br /><br />I don't spend much on oil. Wallyworld SAE30 diesel oil is cheap and you can change it twice for the same money as the other stuff. Judging from the results of using red line above (considered the best of the best), I'll continue with my buy cheap and change more often philososphy.

 

[garycinn]

Re: What causes fuel dilution in an EFI/TBI boat?

Thanks for the posts cobra and seahorse. I think since I got almost 7% after 53 hours I may change every 25 hours with Chevron Delo 15W40 Diesel oil. It is $6.85 a gallon at Walmart. I'll do some more oil analysis in the future to see if this was a freak situation. I'm also going to check out the plugs to see how it's running.

 

[seahorse5]

Re: What causes fuel dilution in an EFI/TBI boat?

Garycinn,<br /><br />Have your engine checked with the appropriate scan tool to make sure that you do not have a temp sensor that is out of spec and "telling" the computer that it is too cool, thus using more fuel than what is needed.<br /><br />Also a fuel pressure gauge test will show if there are any leaking injectors dumping raw fuel into the motor.