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Fuel Pump Fuse and more

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What size should the fuse be, that hangs from the relay attached to the rear seat in the engine compartment? I believe this to be the fuel pump relay and fuse.


First outing of the season, didn't go so hot.  

Seems either I was too late getting it in, or the shop that winterized it failed.  I went to a new place, obviously won't be back, but to be fair I was pretty late, I wanted one more trip.

A bit into the day, we noticed some water where it wasn't always, it's a boat it happens.  A bit later as we were filling the ballast, we started noticing more water.  Hmm, did the dealer leave one of the mid hull plugs out?  Nope, but there is a lot of water in there.  Checking the rear, yeah that's a lot of water.  We immediately reverse the ballast process and head to the dock.  

As we drive to the dock we notice hot water on the floor of the boat, coming from the command console area.   Immediately I know what is wrong.  The heater core has frozen and burst.  

By the time we reached the dock water in general was at floor level, probably a bit deeper in the engine compartment when the boat was tilted driving.

After bringing the trailer down, the boat will not start and we have to walk it around the dock to trailer it.  A bit of time and one smashed toe later, we have the boat safely on the trailer and head home.

Tearing the boat apart to confirm the Heater Core problem:



The heater core.  Just a couple pin holes ;-)

So that problem resolved I moved onto the boat will not start problem after replacing the heater core with a 5/8" coupler.  After several attempts to start without luck I move on to diagnostics.  No engine codes.  Everything sounds good, just not getting any combustion.  Either it is fuel or electrical.  Checking the fuse box all seems well.  I came across this other dangling fues recently so I knew it was there. 



That is the relay and the fuse holder attached to it.

Significant trouble opening the holder and this is what I find


That is my current problem.  There was a 40 amp fuse. I dropped it under the engine so cannot show you, but you get the idea, not blown as it should have.  Given the gauge of the wire, I suspect strongly that the original owner replaced what was a 20 amp fuse with a 40 amp fuse.

I am going to replace the holder obviously but I am wondering if I should put a 20 or a 30 amp fuse in there.  The state of that outlet means that the outlet capacity was exceeded.  The state of the fuse means that the fuse was not the only thing standing in the way of the excessive current, the wires must have been over loaded as well or the fuse would have blown cleanly.  I would expect a 40 amp fuse to be on a 10 guage wire, these look closer to 12 or 14, depending on the thickness of the sheath.

If anyone knows the correct fuse size it would be much appreciated.


What else do I need to watch out for with a freeze situation?  Hopefully the motor was properly winterized.






Bonus points for anyone who can give me a replacement part number or product for that hose, which I suspect is the cause of a perpetual initial overheating problem.  It is located just behind the strainer cup port side,  between the engine and the transmission.


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Eek.  After you replace that fuse holder put an ohm meter on the fuse receptacle to GND and make sure there's not a low impedance elsewhere hidden in the loom. 

Once.  Just once on a project at work we had a receptacle failure that basically opened up partially making the fuse holder exactly the right resistance to burn hot.  Almost the entire current rating of the circuit was burning off over 15V of drop as about 150W of heat at a single point back in the plastic housing.  It did look a little bit like your picture actually.  Technically the current never exceeded the rating of the fusible link in the fuse so it didn't open to protect the circuit.

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Yeah @Slurpee that is my primary concern and why I think an overvalued fuse was used in this place.  I have seen others reference a 20A fuse for the fuel pump, but that was not for this specific boat and as such the value may be different.  With a 40A fuse we are looking at around 480 watt potential before the fuse would fail so if it was over value, that is a pretty big risk.  

I will likely go with a 20A and see how that fares.  If it blows too frequently I may step it up.

Good call on checking with an ohm meter.  

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Wow - I have never really thought about how much water you can put into the boat via a broken heater core.  I have seen shut off valves being placed on both connections tying the heater to the engine to be able to quickly remove the heater from the engines water flow.  I will look more closely now at doing that myself.  Thanks for sharing and good luck with the repairs.

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Yeah I think most heater core leaks are just pinholes.  But with the pipes burst wide like mine the water just kept coming.

Hmm... do I run the motor to get back to the dock and pump more water out the heater core in the process?  

A note about bypass.  Malibu says that water path is critical to engine operation, so you cannot just shut it off, water must continue to flow in and out of the pump through those lines.  So if you add a shutoff, it needs to have a bypass route back to the pump.


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You probably can't shut it off, but if you have a small tube connect from the inlet and outlet (instead of going through the core), you should be good.  I don't have a heater and there is just a small piece of tubing that connects the in/out where the core would be attached.  I haven't pulled mine apart, but I think it just acts as a bypass like you are suggesting.

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Replacement heater core arrived on Saturday.  The 2-4 week wait turned out to be only 1-week, now I just have to put it all back together.

Really wish someone could tell me what size fuse that should be, I have tried the dealer, customer service my post here all with no success yet.  Searched the manuals for the boat and for the motor also with no luck.


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New heater core arrived much more quickly than expected.



I wrapped it in a cereal box to protect the thin fins while putting it into the heater box.



This worked well to protect the unit, but was much more difficult than I expected to remove the cereal box.  But with a bit of effort the fits are not banged up like they were when I removed the damaged one.


Make sure to align it properly with the bracket inside.




Installed and ready to close it up.



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Unfortunately after soldering in a new fuse holder, and replacing the fuse, the boat still will not start.   It turns over but there is no combustion.  I still suspect it is a fuel supply problem.  I found another dangling fuse in the engine compartment that was blown as well, this one behaved as expected and was a simple replace.  

It drives me nuts how bad that melted down and how close it was to the fuel supply.  My boat could have quite quickly become a ball of fire.  It is difficult to see in those pictures how bad the wire was damaged, I'll post some more later.  I think I need to replace that wire and maybe a couple others.  They were melted together where they were taped tightly.  I suspect this is the cause of my current failure to start, though I haven't yet taken the multimeter to the task to make a better assessment.  It has been raining pretty heavily for the last few days.

During the wet time I have been making a mini skirt for my baby to protect the gel coat.  The summer sun has been oxidizing the top edge which is black and turned it grey.  I was able to polish it back to shiny black a week ago with a medium cut product from Meguiars and a 7" wool buffer disk in my DeWalt drill. Took a bit of time, but really went much more quickly than I expected.  I was overly concerned before I started, overwhelmed with the variety of products available for the task.  I wanted a random orbital, but couldn't find anything reasonable or available locally that had decent reviews.  Finally I determined to start with what I had and go from there.  I was afraid of leaving swirls without the random orbit, but this was not the case.  I am still planning to do another pass with a foam pad and a swirl remover, but primarily that is just to give it a super glossy finish, as there are no swirls to remove.  

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I am definitely not sure what that fuse is for.  I will be quite certain this evening as I am removing much of the loom to replace the wires, which will allow me to easily trace them to their destinations.  What I am certain of was that it never should have been a 40 amp fuse in that fuse holder or attached to those wires.  The other I replaced in a similar holder and similar gauge wire was a 5 amp fuse.  I have currently replaced the 40 with a 10 amp for now.

When you say heater boost pump, what exactly is that?  I thought the heater was fed exclusively by the impeller pump on the front of the motor (nearest the back of the boat).  Is there another pump that assists in that?

Damn I just want to be on the water.


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Finally got  a reply from Malibu, they say it is the fuse for the "heater pump circuit harness" and it should be a 20 amp fuse.

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She started!

Going to have to disagree with the "heater pump circuit harness".   It is absolutely the fuse for the fuel pump relay.  The relay is rated at 30 Amp so definitely should have been fused lower than that.  Tracing the wires it definitely leads straight to the fuel pump.  

Not sure why I didn't think about it sooner, if the fuse was fried, certainly the relay was.  I attempted to disconnect the relay in order to access a terminal to test the wires for connectivity and found that the relay would not open.  I started prying with a screw driver and still it did not want to open.  Eventually I was able to remove the relay from the socket. 


Or so I thought.  When I removed it the relay came out with the socket and left the housing behind.  I pried the socket free from the relay.

The relay had clear damage seen by the melted plastic. 


The socket hand similar damage, where the relay and socket had melted together.  A trip to O'rielly and one very confused attendant later I was able to acquire a GM 12193611 which is a direct replacement.

The relay and socket can be had here on Amazon (an affiliate link).

While the socket was damaged, I was able to put the new relay into the socket without difficulty.  O'Reilly did not have the socket available, I will have to order it from Amazon.

The moment of truth.  I press the button she turns for a second then fires!  Hallelujah!   Then she sputters and dies. . . almost immediately I know why, but the ECM has thrown a fault so I go to see what that was.



Looking up SPN 66017 FMI 5 in Google I find "Fuel Pump Relay 1 Current Below Normal or Open Circuit".  If you recall, I used an undersized fuse for my initial testing here and indeed it has blown.  Replacing with a 20 amp per my info from Malibu, I repeat the process and this time she fires and stays running.  Amazing difference fuel in in the engine makes.

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With the heater core reassembled, I again disassembled the console so that I could install the heater-box.  I attached the wires according to the pictures I took when I first removed it.



I mounted the heater core on an angle to aid drainage when I next purge the heater core, as I had seen others suggest.  I am not certain this is best, but that is how it is for now.


I reattached the ducts to the heater box.  The keen eye may notice that I incorrectly attached the breather vent duct initially, I thought there was a heater vent on the port side, there is not.   I corrected this before I was finished and instead connected the second under dash port which I had initially left blank.  Turning on the batteries and testing, the heater is blowing strong and all ports are active.

While I was there I moved the bundle of wires on the left up higher with a zip tie.  I hate that nasty electrical tape the stereo installer used.  It was probably bargain tape, but it leaves a nasty mess on my hands every time I touch it.  If I don't notice, the mess transfers to the vinyl and does not come off easily.

I also re-oriented the anti siphon seen at the bottom of the pictures, so that it is mounted on the left wall with a zip tie in a vertical position, like all of the others in the boat.  I assume this is an anti-siphon for one of the ballast pumps.


With everything back together and the boat starting, I am heading to the lake this evening to see if she is sea worthy.  With luck I'll get in some chilly surfing.

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Glad to see you've been able to get things back moving in the right direction.  Thanks for documenting this on the site.  Great for others when searching.

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Nice detective work. Always good to see things work in the end with a root cause. Hope the water test goes well and thanks for the pics and documentation of this issue.


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Took the boat out this evening and all went well.  

Finally got to surf a bit, though the water is still cold it felt great.

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