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Merc fuel pump that is mounted on sea water pump - PLEASE READ

Old 05-05-2008, 08:22 AM
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Default Merc fuel pump that is mounted on sea water pump - PLEASE READ

Last year (July) I replaced my sea water pump. Thus I installed the fuel pump on it as normal. Of course new oil was used.
Yesterday I removed both pumps to replace impellers/pump housing. I took off the fuel pump to change oil.
The oil had fuel in it and the oil looked HORRIBLE. The oil was gray looking!! That oil had only 20 - 25 hours on it.

Anyway, everyone should check / replace the oil for the fuel pump in the seawater pump. Looks like it needs changing more than even motor oil.

Now - is there a pump that can be mounted in the stock location that does NOT leak fuel into the seawater pump oil reservoir?
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Old 05-05-2008, 12:34 PM
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I have the oil changed in mine every year. it should not have fuel in it. If it does, the diaphram is bad, and leaking. Time for a rebuild kit.


Darrell.
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Old 05-05-2008, 01:35 PM
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Originally Posted by DMOORE
I have the oil changed in mine every year. it should not have fuel in it. If it does, the diaphragm is bad, and leaking. Time for a rebuild kit.


Darrell.
Agreed, diaphragm is shot.
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Old 05-05-2008, 03:13 PM
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Yes, sounds like pump leaking...but I still go by original thoughts from what I have seen, what POS set-up !! and costly to repair !! Rob
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Old 05-05-2008, 04:43 PM
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A nice electric pump replacement sounds good. Anyone ever done it?
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Old 05-05-2008, 07:13 PM
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Previous boat did always had a hint of gas smell to teh oil and the oil was thinned. Thinking the pump diaphram was leaking, I replaced it. Didn't change a thing. Just got into the habit of changing the SW pump oil every yr and never had any issues. Just considered that the diaphram does allow enough fuel to seek thru it to cause this condition.
Seems like a common complaint. If the diaphram really was bad, I'd think the oil level would rise till it shows in the puke tube.
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Old 05-05-2008, 09:06 PM
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I have had this problem with a customers boat also.

I put new fuel pumps and they still get fuel into the oil.

He just works around the problem by changing the oil when he does the engine.

I would like to know if this really is normal or not.
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Old 09-23-2020, 07:50 AM
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Great read
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Old 09-24-2020, 08:00 AM
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There's room under the fill port on the side of the pump where you put the oil in...to drill/tap another hole for a drain port and install a sight plug..(like on a carb fuel bowl) .easier to just look to see if the oils the right color than taking things apart all the time
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Old 07-27-2022, 04:06 PM
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I am going to dredge up a old thread but have a question on this. Is the Merc Racing 520 water pump the same style as the 500? I have a friend that has lost water flow to a motor and I am thinking it is probably impeller but have not been able to put my eyes on them to verify. The information in this thread is great guidance and is similar as to what I did with my 502 but I have not really messed with the HP motors..

Thank in advance.

Last edited by 283Check; 07-28-2022 at 09:21 AM.
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