I have 7.4mpi's today I installed brand new stock mercruiser not cheap aftermarket manifolds&risers because I thought the cmi headers were having issues. While running on the hose it turns out the port exhaust tip is dryer on both engines. Less than half the water coming out the back!!!

These are closed cooled blocks raw water everything else and the heat exchanger feeds the manifolds. Could it be the exchanger is clogged with rust and corrosion? I removed the hose connecting them and it looks like rust but no chunks or mess of any kind. Where else should I look?

I have the thermostat housing from the engines I pulled so I can convert and eliminate the closed cooling system if that's the solution. Definitely not buying a new heat exchanger.
Before:


After:

it is not uncommon to have one side hotter than the other on the garden hose.anything above idle rpm and the garden hose can not provide the volume of water the sea pump will suck.put the boat in the drink and you should be good.

What he said^^^^^^^^^^^^^

^^^ Agree with these guys. And I recommend, NOT using those fram filters.

The direction of flow in closed cooling will always favor the starboard side. I put a water pressure gauge to eliminate the guess work.

+1 on those Fram filters, they're junk. Tore a fresh motor down looking for an oiling issue to find out the issue was the filter. Been running K&N HP3002's ever since.

Cool thanks guys. I'm gonna drop her back in and see how she runs.

I went to Walmart and bought 6 filters and 10 gallons of oil changed the oil 3 times on each to get the milk out. I have the quick silver ones but the oil was clean before I ran out of Fram filters. I'll be changing the oil again soon and never using Fram again.

most all marine engines will run hotter on one side of the risers / manifolds even in the water. The 496 is the worst for it. Part of the problem is unequal water flow and travel distances through the engine.

Yea seems about right. The route and distance to the manifolds being unequal... I dropped it in the water and both sides are cool to the touch. Now i have another issue with the props or hopefully just the hub.

just had the same issue on a friends 525SC found that the oil cooler had gravel in the screen

Wix/NAPA Gold is a good choice for an oil filter, and you can pick them up at any NAPA.

What caused the milkshake in the engine? Were the CMI's leaking?