MerCruiser Raw Water Problems

[MikeMahler]

have a MerCriuser with a 350MPI Horizon motor that is Fresh Water Cooled. Even with the Fresh Water cooling I flush the moter after each trip to clear the salt out of the raw side and manifolds. Last year the raw water pump stopped being able to pick up its prime with flushing muffs on the outdrive so I pulled the pump apart and replaced the impeller. When that didn't correct the problem I thought that I might have too much scaring on the housing for the new impeller to work right so I replaced the entire pump. This still didn't correct the problem.

I backflushed the intake side and water seems to move freely from the pump intake hose to the outdrive. I also found that if I squeeze the muffs to force water up to the pump the it will start working.

Any suggestions on where I should look next?

 

[Don S]

Re: MerCruiser Raw Water Problems

What's the SN of your engine? What outdrive, even a year would help some. What kind of raw water pump is what I am trying to find out.

 

[MikeMahler]

Re: MerCruiser Raw Water Problems

It is a 2004 350MPI Horizon with a Bravo-3 Outdrive. The Raw Water pump is the Bronze model mounted on the lower starboard side of the engine. It has the vacum ports for that single point drain system.

 

[MikeMahler]

Re: MerCruiser Raw Water Problems

Serial Numbers:
0W016419
OW223360
OW120085

 

[Don S]

Re: MerCruiser Raw Water Problems

It has the vacum ports for that single point drain system.

Those are NOT vacuum ports. They are pressure ports. They open with a small hand pump mounted on the front of the heat exchanger.

MAKE ABSOULTELY sure that ALL the air is off that single point drain system, or it will open the system and allow it to suck air.

 

[MikeMahler]

Re: MerCruiser Raw Water Problems

Yea I checked that and I checked to make sure that plunger was free to move back into the closed position.

I will be pulling the outdrive off this weekend to do my spring check of the U joint and bearing. Maybe I will find something there.

With my problem being getting the water started moving and once I get flow everything seems to be fine I think my problem is an obstruction or air leak on the intake side of the pump. Am I on the right track here or should I be looking at my heat exchanger and manifolds too?

 

[Don S]

Re: MerCruiser Raw Water Problems

I will be pulling the outdrive off this weekend to do my spring check of the U joint and bearing. Maybe I will find something there.

You should actually be doing that in the fall when winterizing. That way if there is water in the bellows it doesn't have all winter to corrode and rust things together.

Since you do have an engine mounted raw water pump, you could actually use this Volvo diagnostic procedure for overheats. The principals are exactly the same.

http://www.4shared.com/account/file/50572185/e88f1d89/Volvo_Penta_Overheat_Diagnosis.html

 

[MikeMahler]

Re: MerCruiser Raw Water Problems

Problem Fixed. When I pulled the seawater pump apart I was surprised to find that the impeller in the brand new pump had a ?set? in the blades. They were not expanding on the intake side of the pump to give a good seal. Thinking about it I guess there is no telling how long the pump sat in a warehouse before I bought it.