2018 SL Dual ballast fill issue

I've been troubleshooting a problem with the ballast system on my 2018 SL450 for a while, and hope that someone on here can help me figure it out.

My SL has dual ballast pumps to each bag that split off a single through hull. I noticed my left ballast was filling much more slowly than my right. After some troubleshooting, I realized that the left pump was spinning, but not pulling water. It's bone dry, and gets very hot as you can imagine. I checked the impeller and it is (suprisingly) fine. As an experiment, I disconnected the pump that was pulling. With that pump disconnected, the other pump began to function again. One thing that I am thinking may be an issue is that the non-pulling pump is mounted about a foot or so higher than the other pump. But it has always been mounted this way, as is the right side pump. And I assume that all SL's are set up this way. My dealer hasn't seen the problem before, and between us we are basically out of ideas.

I appreciate your help, as always!

I have no issues with mine priming or pumping. They overflow at almost the exact same time.

Have you tried replacing the impeller? Some guys on this forum have commented that an impeller May look fine but wasn’t good.

Either the impeller isn’t spinning or there is an obstruction in the line. If the impeller was run dry for that long it would show damage of some kind. Maybe the pump shaft is spinning freely in the hub?

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Originally Posted by pedel

I've been troubleshooting a problem with the ballast system on my 2018 SL450 for a while, and hope that someone on here can help me figure it out.

My SL has dual ballast pumps to each bag that split off a single through hull. I noticed my left ballast was filling much more slowly than my right. After some troubleshooting, I realized that the left pump was spinning, but not pulling water. It's bone dry, and gets very hot as you can imagine. I checked the impeller and it is (suprisingly) fine. As an experiment, I disconnected the pump that was pulling. With that pump disconnected, the other pump began to function again. One thing that I am thinking may be an issue is that the non-pulling pump is mounted about a foot or so higher than the other pump. But it has always been mounted this way, as is the right side pump. And I assume that all SL's are set up this way. My dealer hasn't seen the problem before, and between us we are basically out of ideas.

I appreciate your help, as always!

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Mine did the exact same thing, the impeller looked fine. Changed the impeller and works like a charm. Mine just had tiny little flat spots in the impeller, it was enough to make it not prime. It only happens in the pumps that are mounted higher. Make sure the inside of your pump is totally smooth too, that way the impeller will last longer.

Thanks for the feedback. I pulled the impeller and it literally looked brand new so I put it back in. I'll take your advice and replace it.

thanks again.

Just to follow up...

I replaced the impeller, and cleaned up the inside of the pump, and it seems to be working again. I also remounted the pump lower to try to avoid the problem. The more I look at it, I think this is a design problem with the implementation. The second pump is not only mounted higher, but also has a much longer tube running to it than the other pump. Therefore, the lower/closer pump gets primed first and if the upper pump doesn't have enough pull it never gets primed (and spins dry indefinitely). My impeller looked totally fine, but maybe there is the slightest difference that causes it not to have enough pull. If they want to run two pumps off of the same through hull I think they need to mound the pumps right next to each other with the same length tube at the same height.

It's also interesting that adding the second pump doesn't double the fill/empty time. With both pumps running it fills in 7:30 min. With only one running it fills in ~11:00 min.