1998 t 200hp mercs efi water flow & over heating

[ALANSR]

I purchased a boat in Maryland with twin 1998 200 hp mercs efi. The water at Maryland is very mercky. Both engines have the same water flow problem and overheating. Here are some of the things I have done with no sucess. Replaced the impellers and housings, Replaced poppet valves, replaced, altered, and removed the thermostats, I have blown air and water at high pressure (about 150 psi) through the pipe after removing the lower units. I have put commercial radiator cleaner through the engine Nothing works. I left the engine without thermostats and I still get about 180-200 degrees when trolling and about 170 degrees at 5,000 rpm's. water flow is still low at 5,000 rpm's.

Please advise on the issue.

 

[Faztbullet]

Re: 1998 t 200hp mercs efi water flow & over heating

Are these the 2.5 liter efi's or 3.0 liter Optis?

 

[ALANSR]

Re: 1998 t 200hp mercs efi water flow & over heating

They are 2.5 L

 

[Faztbullet]

Re: 1998 t 200hp mercs efi water flow & over heating

Was boat left in water all the time or trailered? What you have is a restriction caused by:
1) growth in the water pickup area under the water pump base
2) restricted water supply tube from pump to powerhead
3) hole erodded in water tube to powerhead
4) debris in exhaust divider plate