1995 Alpha 1 5.7 Cooling, which gaskets? which thermostat? how to 'flush'?

[jesse_boston]

Slowly working through sorting what the previous owner didn't do quite right on my boat (1995 Doral 230 EX).
It has a 1995 Alpha I gen II, with the 4 barrel 5.7 thunderbolt 4 engine (serial 0F297698).
The engine overheats.

I have a new impeller kit that just arrived on my doorstep.
Going to pull the risers and elbows and inspect the manifolds and flappers.
Also going to pull the thermostat housing to inspect that, and to change the thermostat.

I've read that a carb engine should be running a 140 degree thermostat, efi 160. I've also read that a saltwater boat should be 140, freshwater 160.
The Mercruiser parts site specifies 160 for my engine, which has a carb, and though it has so far been a freshwater boat, it will be used about 50% of the time in saltwater.

Question 1: Should I get the 160, or something else?

Question 2: As for the riser gaskets, which ones should be in there? The parts site specifies half open for "standard" cooling, full open for "riser kits". I don't trust the PO to have done anything right, so I'm not going to replace like for like.

Question 3: What is an "acid wash", as opposed to just "flushing" the cooling system? How best to remove scale/rust/sediment/etc if the passages and parts are restricted or scaly?

Apologies that I'm sure these questions have already been answered dozens of times... trouble is I'm seeing different responses in different places and I'm just not sure anymore.

Thanks!

 

[alldodge]

Q1 - I would use 140 going into salt

Q2 - If you do not have riser "extensions" then just need half. If you have risers, then full is used on mans, and 1/2 is used on top of risers before elbow is connected

Q3 - Use acid wash only if the block and exhaust is clogged up. Can use things like barnacle buster if there is marine growth in side. If its just some muck, just flush and remove drains

 

[jesse_boston]

It is a bit clogged up...
Jackets look good, but big pieces of rust/scale inside them if looking close...

 

[alldodge]

Those look bad, and with elbows looking like that the mans are probably even worst

 

[Scott Danforth]

those risers are burnt toast. you need new risers, and most likely new manifolds.

 

[jesse_boston]

Ordering a new set of manifolds and risers now. Yeah the manifolds *might* be okay, but I also *might* destroy the engine if they are worse than they look.

I actually ordered a set of mercury marine stainless risers last night, but am I correct in thinking that using stainless risers with cast manifolds in a raw water cooling setup is a horrible idea?

 

[Scott Danforth]

Mercruiser put stainless risers on the 8.1s with cast iron manifolds