mercruiser 4.7 manifold and riser replacement

[cpoint]

Here we are another season is over, when it starts, I am already lined up with work
Basically I was told I need to replace my mercruiser 4.7 manifold and riser on both engines, as I have been apparently very lucky that my 2000 carvers original manifold and riser have not given up yet, but they are ticking bomb at this point. I did research and looks like that I have been lucky, as these things needs to be replaced every 5-6 years I read everywhere and been told by everybody. So there goes more green stuff Any input, suggestions, comments appreciated as always. Luckily, so far nothing happened, as in water leaking into engines.

[tomschauer]

I assume have 5.7's not 4.7's as listed. Are they raw water cooled or fresh water cooled? If they are fresh water cooled you most likely only need to replace the risers.

[buster53]

Source of the post I assume have 5.7's not 4.7's as listed. Are they raw water cooled or fresh water cooled? If they are fresh water cooled you most likely only need to replace the risers.

Tomschauer is correct. If you have a full fresh water cooled engine where the manifolds are included in the closed cooling system, as far as rust and corrosion goes, they should last as long as the engine block. Risers/elbows are a different story. Depending on how salty the water is you boat in, they could only last maybe 4-8 years.

[mjk1040]

I think he meant 7.4L engines if it's a Carver 356! Riser replacement time frame would depend on what type of water the boat has been in. If you are in salt water, then yes the time frames you were given is about right. I'm in fresh water non salt and our are original from 1998 on our crusader's!

[darrenlife]

Either way, use a generous amount of liquid wrench and let that soak in. You should be able to see the shank of the long boat on the side of the riser, use this to sight if the bolt is attempting to turn as you apply torque to your socket handle. Go slow, you won’t want to deal with a broken bolt.

[buster53]

Source of the post Either way, use a generous amount of liquid wrench and let that soak in. You should be able to see the shank of the long boat on the side of the riser, use this to sight if the bolt is attempting to turn as you apply torque to your socket handle. Go slow, you won’t want to deal with a broken bolt.

Liquid Wrench or PB Blaster...don't just use it, use it a couple of times and even run the engines a few minutes between soaks over a couple of days. The vibrations of the engines running will help the penetrating oil soak down the threads of your bolts.

Agree that the OP meant to say 7.4's. A 356 needs big blocks, not 5.7's.

[tomschauer]

Most likely 7.4's, but the 355's and 356's were available with 5.7' mags.

[cpoint]

Source of the post I assume have 5.7's not 4.7's as listed. Are they raw water cooled or fresh water cooled? If they are fresh water cooled you most likely only need to replace the risers.

No, not fresh water unfortunately.

[cpoint]

Sory, typo 7.4 MPI. Also it is in brackish water.

[tomschauer]

Then it most likely time to change before they leak water into the cylinders.