Vapor lock
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Vapor lock

  1. #1
    Senior Member HEMETDRAGRACER's Avatar
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    Default Vapor lock

    The last 2 trips out Ive had issues with vapor lock, Engine is a Mercuiser fuel injected 502 in a 98 Ultra Stealth, I originally thought it was the fuel, I drained the tanks, changed the fuel filter/seperator, and tried again, then the fuel pump failed, so I thought that was the issue, changed the pump, and still having the issue... any thoughts or suggestions? This is happening after I run it, park it and try to restart after a half hour or longer...
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    Senior Member Schiada 201's Avatar
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    If the fuel line to the carb is all steel, cut and put in a section of rubber fuel line.
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    It's what we do BDMarine's Avatar
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    The problem is the cool fuel pump assy. The body of the pump is steel and All the lines in and out are steel. We have had many customers throughout the years with the same problem and my own boat had the same engines and the same problem. When you shut the engine off and the hatch is closed the temps sky rocket. I used to carry a cup and pour water on the fuel pumps and lines and would solve the problem.
    The bottom line is you need to cool down the engine compartment. It needs more ventilation and a way to cool down instead of heating up when the engine is shut down. We have installed bilge blowers that blow fresh air on to the cool fuel pump and had good success with that. It is wired with the other bilge blower so it also helps circulate the air.
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    Senior Member HEMETDRAGRACER's Avatar
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    Quote Originally Posted by BDMarine View Post
    The problem is the cool fuel pump assy. The body of the pump is steel and All the lines in and out are steel. We have had many customers throughout the years with the same problem and my own boat had the same engines and the same problem. When you shut the engine off and the hatch is closed the temps sky rocket. I used to carry a cup and pour water on the fuel pumps and lines and would solve the problem.
    The bottom line is you need to cool down the engine compartment. It needs more ventilation and a way to cool down instead of heating up when the engine is shut down. We have installed bilge blowers that blow fresh air on to the cool fuel pump and had good success with that. It is wired with the other bilge blower so it also helps circulate the air.
    Thanks, unfortunately a scoop isnt a option, Im thinking Im gonna relocate the filter to the opposite side to make the hoses shorter and to keep the hoses from crossing across the engine... hoping this will help... anyone ever had trouble with the IMCO fuel selector? Its the big electric one... just wondering if it has a internal check valve that could cause this...
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    Quote Originally Posted by BDMarine View Post
    The problem is the cool fuel pump assy. The body of the pump is steel and All the lines in and out are steel. We have had many customers throughout the years with the same problem and my own boat had the same engines and the same problem. When you shut the engine off and the hatch is closed the temps sky rocket. I used to carry a cup and pour water on the fuel pumps and lines and would solve the problem.
    The bottom line is you need to cool down the engine compartment. It needs more ventilation and a way to cool down instead of heating up when the engine is shut down. We have installed bilge blowers that blow fresh air on to the cool fuel pump and had good success with that. It is wired with the other bilge blower so it also helps circulate the air.
    I have had a similar issue, a Mercruiser factory tech told me that Mercruiser doesn't want to see an engine compartment temp above 140 degrees. I ran my blower on all the time this past weekend at Havasu and didn't have a problem!!
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  8. #6
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    Search the web for Mercruiser service bulletin No. 99-7. It will tell you everything you want to know about vapor lock and how to prevent it.
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  9. #7
    Bass Lake Dream'n "Flat" foot'n's Avatar
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    Back in the day when I was a Merc tech I placed a temp prob on the bottom of an engine hatch just above the fuel rails. It reached above 200 deg in 15minutes!
    My brothers 24' Lavey does it, He has to either leave the hatch open a little or just manually bleed the vapor from the fuel rails via the test port.
    I don't think relocating the filter will do the trick. The vapor lock happens in the fuel rails.
    Let us know how it works...
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  10. #8
    Junior Member Laser Boy's Avatar
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    I had several friends that had the same problem and we found that Marine Formula STA-BIL works best.
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  11. #9
    Senior Member Trim it up's Avatar
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    Happen to me about 2 weeks ago. I have a 25 daytona with a EFI hp 500. My mechanic said alot of his customers are having the same problem. Just the awful weather. Crack the hatch when you start it and run the blower. He also told me about bleeding the fuel rail if needed as last resort.
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  12. #10
    It's what we do BDMarine's Avatar
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    BE VERY CAREFUL BLEEDING THE TEST PORT!!! You are letting fuel and fuel vapors escape onto the hot engine and the vapors will go to the bottom of the bilge. A very dangerous situation. Even if you are very careful, I do not recommend doing this.
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  13. #11
    Can't re-Member 28Eliminator's Avatar
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    I had the same problem at the beginning of the year. Turned out to be the Anti-siphon valve at the tank causing the problem. It was hard starting sometimes, and when I throttled up it would just start to get on plane then die. Waited a few minutes and it would start, then be fine. Drove me nuts.

    Replaced the anti-siphon valve, and no more problems (and it has been a lot hotter lately than when I was having the problem).

    Just a suggestion.
    I'd agree with you, but then we would both be wrong
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  14. #12
    Senior Member kevnmcd's Avatar
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    Quote Originally Posted by BDMarine View Post
    The problem is the cool fuel pump assy.
    Exactly! I used to have this same problem on my 502 and found that if I let the engine idle for a few minutes after running it hard to bring the motor temp down before turning it off it would really help with the vapor lock. When I rebuilt mine motor, I completely removed the mechanical fuel pump and the cool fuel pump assembly which housed the electric fuel pump and added a aftermarket electric fuel pump and fuel pressure regulator. Haven't had vapor lock once since the conversion.
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  15. #13
    Senior Member HEMETDRAGRACER's Avatar
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    Well, problem seems to be gone, I moved the filter, I mounted it to the wood, cargo divider, on the opposite side of the engine, this took about 3 ft of fuel line (that ran near the exhaust) I also replaced my impeller which was starting to fail... and last but not least I filled up at river island instead of terribles... problem seems to be solved... Thanks for the help and ideas guys...
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