First time changing Impellers - 1990 350 EC twin 454 Merc Inboards

[rmarkko]

Hey guys, Although, I've piloted many boats for some years, from parents to co-owned boats, this is my first solely owned boat, so I'm a little new to boat maintenance.

I'm getting ready to do my first (of many, i'm sure) impeller replacement to hopefully solve a water flow issue I am having. Can anyone offer me an tips/best practices/ or any diagrams/imagery they have on this before I dig into it?

Previously the guy I co-owned my boat with did a majority of the maintenance due to my travel schedule. I am now realize what a disservice I did myself, and want to learn and do as much as possible myself from now on. As always, thanks for all the help!!

Richard

1990 350 Express Cruise
Twin 454 Mercruiser Inboards - raw water cooled

 

[GrandMaster]

There are generally a lot of videos on YouTube that you will find helpful provided you use the proper search criteria

 

[Quint4]

Here is a quick and dirty general overview:
- Your impellers are mounted in a pump body on the lower left of your engine (looking at engine from the front).
- You probably have the "dual style" pump assembly that also has your fuel pump.
- Close the seacock coming from your thru-hull serving each pump before beginning (assuming you are in the water).
- Remove hoses from back of pump (use a white paint pen to mark one hose and its fitting.....prevent a mix-up at re-assembly).
- It may be easier to remove the belt and entire pump assembly but I managed to do my 454 with it left in place.
- Remove bolts and nuts from back of pump to reveal impeller......note vane direction of impeller.
- Needle nose pliers to remove old impeller ( if not intact look for pieces in cooling passages....backflush)
- Use a hose clamp around new impeller to keep vanes bent when you put it back in pump body
- Dish soap to impeller to prevent dry initial start up and ease insertion.
- Prepare bystanders for lots of foul language throughout procedure.

A few pics:

 

[Quint4]

Here is the "hose clamp" trick I spoke of. This is a shot from my current boat....different engines but wanted to show the method:

 

[Ricochet]

I would suggest two things, replace the entire impeller housing, I replaced mine this year after 3 years, the impellers were ok but the housing showed wear. Also the clamp idea is great but use a large plastic cable tie....less likely to damage the new impeller. If it is going to sit until spring use grease on the impeller so it will still be lubricated in the spring.

 

[Air O'Nautical]

Changed many impellers on gas engines.

I find on all the Mercruiser pumps its easier to remove the whole pump on the bracket, even if your having to remove the fuel pump along with it.
This way your working standing upright as opposed to working on your head or bent over killing your back.
You will (or should) end up changing the pump and housing as a unit....now is the time because, you spent the effort to remove it.
The newer kit is all plastic with a stainless wear plate, seal and O-ring, it works well and cost around $100.
The soaped-up impeller will twist in by hand or the plastic zip tie is a good trick too..
Also, if you have a mechanical fuel pump collocated on the water pump bracket, change the gear oil in it.
Put it all back and remember what tools it took for next time in 100hrs or three years.

Good luck,

Mark.