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500 EFI Mechanical Fuel Pump Issue

Big Chorizo

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Doing maintenance on the boat today and went to check the oil level on the raw water pump. The oil seems to be diluted with fuel, im guessing the fuel pump is bad?
 

Runs2rch

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Normal. Just change the gear oil in it.If the diaphragm is bad it will push fuel through the vent tube/hose.
 

Big Chorizo

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Oh, ok. Glad I asked. I pulled as much of the old oil out through the plug on the side and topped it off. Doesn’t seem to hold very much before it starts to leak out. Thanks!
 

Riverbottom

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I just did this today on my new to me Merc. Could not get much out the plug, so I removed the fuel pump and sucked the gas out the top. Mine was real diluted almost straight fuel. Filled it up to the plug. I think maybe drill and tap the bottom of the cavity with a pipe plug to drain the contaminated oil and fuel.
 

Big Chorizo

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I just did this today on my new to me Merc. Could not get much out the plug, so I removed the fuel pump and sucked the gas out the top. Mine was real diluted almost straight fuel. Filled it up to the plug. I think maybe drill and tap the bottom of the cavity with a pipe plug to drain the contaminated oil and fuel.
Yeah, it’s damn near impossible to get it all out without removing it. I ended up pulling the pump completely off as well, basically rebuilding all of it. The front seal was leaking behind the pulley, replaced the fuel pump too being that it’s 17 years old.
 

bocco

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I just went through the same deal earlier this year. I pulled the whole pump deal and discovered fuel in the oil for the second time since I've had the boat. I replaced the fuel pump and that was probably a waste of money. My new maintenance plan is to pull the whole deal every other year to change the impeller and the pump lube. I think that the way the pump is mounted vertical you will get fuel in the oil before you see it in the vent tube.
 

Riverbottom

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I don't know if it is still available, but STP used to be really thick and is oil based. I might fill it up with that next time. Would take a while to dilute.
 

Lavey 29

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you can pump the oil out with the same as many use to suck engine oil thru the dip stick. I have done a zillion that way. They do not hold that much either and a lot are mixed oil with fuel . It is best to take them completely off as well to check the lobe and all that rotation
 
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