Rust in Water on Startup

[Tacoma290]

My port side 8.1 was replaced last year with a long block (Michigan Motorz), and all has run well since. I have noticed that on startup, a good amount of rust colored water comes out the exhaust on startup on that engine. I know a little is normal for a boat in salt water, but I see much more on the port than on the starboard side. Perhaps as an aside, I have noticed that the engine coolant is little darker on that starboard side than starboard (I thought this was due to a remaned enine and was going to dump and flush that side, but they could be related...). I am thinking of pulling the heat exchanger since the old one was re-used and original. But if I pull it, I might as well replace with new. What do you all think?

Relevant info:
-Boat is kept year round in salt water.
-I do flush with fresh after running the engines.
-The exhaust manifolds were new 1 year ago on both sides.

 

[Golfman25]

The longer my old boat sat, the more rust I would have come out the exhaust. A good run usually cleared it for a while.

 

[northern]

Are the manifolds and risers the same manufacture on both sided