I put brand new water pump housings and impellers on my boat last year and had no problems cooling. This year after I finally got it into the water last week and ran it. I overheated the port engine and blew the head gasket (mercruiser 470). I always had the muffs on when I was running it on land to winterize it. The impeller and housing is less than a year old. The boat spent 1/2 the season last summer in the water all the time. This year, it hasn't even been in the water once. It looks like the vertical shaft is flexing and oblonging the hole at the top of the water pump housing. And small chunks are missing from 2 vanes and a third vane is cracked vertically. Has anyone seen a upper water housing oblong like that?

I saw this same oblonging of the water pump housing on another Alpha outdrive too

first question who impeller and housing is installed ? Looks like Sierra with the white plastic housing.

Next is ---- those are a once per year impeller changes because they are very small vaned and become very hard within a year or 2.

Can careless what the general pop says about that, Once per year change whether you use the boat or not is a no brainer when it comes to proper cooling , Impellers go bad sitting in one spot faster than if they are rotating all the time. Also new gaskets and most of the time the SS wear plate needs to be changed as it gets grooved, Even the slightest groove cause cavitation.

Also really indepth looks at the plastic housing and SS cup and blistering or discoloring it needs to be changed as well. . Also complete kit and some times the lower base needs to be changed upon further inspections. The lower base will blister and or warped --- many miss that as it never gets pulled and inspected.

Another problem is the water pocket assembly gets melted and causes overheating as well. Many miss that when changing the impeller, The water pock assembly is in the upper just above the impeller housing when all is mated back together.

The Merc 470 is a cast iron 460 FORD cylinder head mated to an 4 cylinder aluminum block out of Merc racing back in the day up to 1993. It is long gone and getting harder to get parts for as well.. Also problems with that 2 dissimilar metals ( head & Block ) and warpage very common with those engines along with blown head gaskets. Back in the day we use to see that engine bend push rods as well.

Yes, they are sierra water pump housings. Any idea on why the top of the water pump housing is oblong? It would seem that the vertical shaft is moving around but this is the second Alpha outdrive that I have seen that on.

That assembly was used without water. It's melted. It's not uncommon to see. Doesn't take long to do that damage. Replace the entire water pump assembly including the upper and lower housings.

Everyone here has given you good info.
one thing I will add is to check the inlet for debris.

i have seen some weird things that caused them to overheat.Plastic bags.leaves etc.

Whatever starved it for water may already be gone but it never hurts to check it so it doesnt happen again.

Also when water starved the exhaust heats up. The outside of that housing is in the exhaust path. So it is getting cooked inside and out at the same time. If vert shaft was moving around, you would need outdrive, not water pump.

I wish I could agree with you but every time I started it on land I had water muffs on it. Ive probably ran it on land on the muffs twice since last year when I pulled it out of the water. I'm going to replace the whole water pump in both outdrives and check for debris. Here is something that might be a reason. This outdrive has the slip on exhaust hose coupler that mates to the outdrive when the drive is down. I was thinking that while running it on land the outdrive was up a little and not letting all the water coming out of the exhaust flow over the water pump housing. Does this seem plausible?

you better buy the whole complete kit including the very bottom base. If not you need a whole lot of luck for not burning this up all over again.

you need the top seal on the drive shaft that sits on the very top of the of the plastic impeller housing. That comes in the complete kit.

do not put grease on the impellers either.