I would look in the system like the power steering cooler that this sand is not still clogging Something. I say this because if you use a OEM mercruiser or quicksilver impeller it should be lasting longer, unless it was sitting for years on the parts shelf.
also if sand got in there there may be scoring of the housing.
i have changed perfectly working 6-10 year old merc impellers that are in perfect condition. Everyone complains about the alpha one impeller location but there is no free lunch. If you look at where a lot of the engine driven pumps are they can be a pain to get to and you still need to block the water flow off if it is in the water. you also have a very easy engine compartment with a 3.0 i always enjoyed working on mine.
personally i am a fan of the alpha design, simple, inexpensive (as far as boats go…) and durable.
in my opinion stop screwing around , bite the bullet and fix it correct so you can enjoy a beer on the water… also check that you have no blockages from pulling in sand and look up in the water connection in drive upper. If you pulled enough sand to notice You may have interrupted water flow and melted the orings or plastic parts and impeller is fine just leaking water down stream.
how big is the Wannsee? I visited Chimsee by Chemung in 2013 absolutely pristine and gorgeous
Well, I don't think theres any sand still in the system (no power steering). It wasn't much in the first place really, as I just felt the boat dragging a bit on the sandy bottom, shut it down straight away and punted it into deeper water with a boat hook. The engine ran fine afterwards, with no cooling issues, even at idle for the rest of that season and another season too (summer 2022). Also I drained the block and manifold into a bucket to check for sand, and the drains ran clear, with no obstructions or sand coming out.
I suppose (expect) the housing and or wear plate might be scored a bit, but I dont really think theres a blockage, due to the water flow being fine at speeds just above idle. Ive replaced an impeller before on a boat where the owner ran the boat out of the water for no more than 1 minute (so I was told), and this had a similar issue (no water at idle, more at higher rpm). This impeller looked fine, apart from the usual set to the vanes, but was obviously worn / damaged enough to impair the pumping ability at low rpm. A new impeller cured the problem completely. This leads me to believe that Alpha 1 impeller still looks good even when its slightly worn or aged.
Anyway, Im sure you're right. Im going to look at the boat one more time next week then make a decision as to whether its got to last the summer, or to bite the bullet and fix it now.
Cheers!
PS the Wannsee is a large lake, actually a widening of the river Havel, and part of a system of other interconnected smaller lakes and waterways. Wannsee itself is maybe 15km long and up to 1km wide in places with plenty of sheltered bays for swimming, restaurants with mornings, and a designated water ski area. Generally 2-3 m deep, with the deepest parts being 8m. Here's a pic of the northern end, my mooring is at the top left of centre, in front of the white buildings. If you look to the right, just in front of the city of Berlin in the background, you can see the Teufelsberg, an artificial hill made from rubble from the bombed city after the end of WW2, which during the Cold War was an American radar station and 'listening post'. You can still make out the remains of the towers on top.
Ive also been to the Chiemsee, and taken a (rowing) boat out there - very nice area.
