525EFI CMI Port Header Hot
 

Hello, I have a 2005 29 Fountain with the stock Mercury Racing 525EFI engine and CMI headers. Boat has approx 200 hours. First 75 hours in salt water, remaining hours all fresh water. I recently started the boat to warm it. After about ten minutes of running at idle I noticed the port header was very hot to touch, but the starboard header was cool to the touch. Anyone else experience this? Is this normal or something I should be concerned about? If it’s a problem, any ideas what the fix might be? Thanks in advance.

I had same issue on a 502 efi with closed cooling system. I noticed the port side exhaust had poor water flow, are experiencing this also? I believe 525's are closed cooling too. I Pulled the end caps off the heat exchanger and found sea weed inside. Cleaned it out and it was fine.

Header may be leaking
 

If you have excess oil temp also, after the thermostat opens you got a crack or pin hole in the cmi header. I have had this issue twice...find the pin holes and weld them up. CMI told me to cap it off pressurize to 65 lbs submerge in water and wha-la leak showed right up. $20 to weld up or $5,000 for new ones....