Manifold/ Riser Question 8.1 Horizons

[douglee25]

I would not suspect manifolds and risers right away. They are practically new if it was done in 2017. Heck there isn't even a rust stain on the manifold. Plus with it being a closed system, I'd look somewhere else. How is the water flow out the exhaust?

 

[Misterhelms]

I would not suspect manifolds and risers right away. They are practically new if it was done in 2017. Heck there isn't even a rust stain on the manifold. Plus with it being a closed system, I'd look somewhere else. How is the water flow out the exhaust?

The seller bought the boat in ‘17 and hasn’t touched them. He was the 2nd owner and no one seems to know what took place with the 1st owner. Water flow looked decent - that was my original thought - blockage. Especially with one of the risers performing well.

 

[CaptRonn]

Each water pump for an 8.1 will run about $500 for the assembly plus labor. They’re a PITA to change. Not mechanically difficult, but logistically as each one is directly under the engine in that ridiculously tight bilge. I’d expect a mechanic to likely charge you $1500-$2000 to replace both, parts and labor.

Why replace the whole pump?

Typically all that’s needed to replace is the impellers which are $25 or so each.

 

[CaptRonn]

The seller bought the boat in ‘17 and hasn’t touched them. He was the 2nd owner and no one seems to know what took place with the 1st owner. Water flow looked decent - that was my original thought - blockage. Especially with one of the risers performing well.

So if you don’t mind, what year is this boat you are looking at?

 

[Misterhelms]

So if you don’t mind, what year is this boat you are looking at?

It’s an ‘07 with about 890 hours on the engines

 

[M Prod]

Why replace the whole pump?

Typically all that’s needed to replace is the impellers which are $25 or so each.

Brass housings get scored on these. Pump becomes less effective, and eventually ineffective. I got sick of replacing mine and got the Harden stainless ones now.

 

[CaptRonn]

Brass housings get scored on these. Pump becomes less effective, and eventually ineffective. I got sick of replacing mine and got the Harden stainless ones now.

Ok. I haven’t had that experience, just replace the impeller and move on.

 

[Jimmy Buoy]

I'd be replacing the impellers. Inspecting the old ones will give you a clue if they are responsible for the apparent lack of cooling at higher RPM's. As they age, the impellers take a "set" and don't flex like they should to pump water - especially at higher RPM's and higher torque requirements.

If the impellers are "set" in a perma-curl or if the impeller veins are cracked new ones may be the fix. I can do mine in about 2hrs (but my engines are facing forward with lots of space). You should also inspect the impeller housing for scoring at the ends of the pump. It's a bronze casting which can score badly if sand is ingested with the cooling water which gets trapped at the ends of the spinning impeller. If it's badly scored the pump will not provide as much flow which could cause overheating. There is a kit available which uses stainless wear plates at either end of the impeller along with a custom shorter impeller for about $100. Mine has worked well for some years now.

The risers on the 8.1's are constructed from stainless steel and don't usually require replacement. The manifolds are cast iron (the very early ones were cast aluminium which weren't a good idea in salt water) and do rust with sea water passing through them. They are NOT cooled by glycol on the 8.1's. That's why others are saying they last for 5yrs or so in salt water. If the manifolds fail it almost never is from the dry joint design. It is from failure of the casting inside the manifold itself and the cooling water leaks through the failed iron either inside to the exhaust port area or to the outside into the engine room. Leaks inside are of course, not visible and can cause the exhaust valves to rust over time and even result in hydro-locking the engine if the leak gets severe.

My money's on the impellers needing replacement and possible wear on the pump housing itself.