I have a 2005 Fountain w 525s, original CMI headers, 260 hrs. The port side back header tube from the # 7 cylinder / back of engine, has been showing signs of running hot at the bend about half way up the header tube. The tube is a light bronze colour only at the bend. It appears to get hot when idling, but cools if I run the engine at higher rpm. There is obvious water restriction at this point, possibly from an object. However I was advised it could also be the header design where the water jacket is too narrow. My questions are: 1. should I pull the header now to check for a possible obstuction or is there a way to back flush this tube while still on the engine. 2. Is this a common occurrence with headers, and should just monitor it to ensure it doesn't get worse. I will be pulling the headers during the off season for pressure tests. Thanks

Check for blocked water flow from the water manifold pipe on the bottom of the header. How often do you drain the headers? They fill up with sand.

I drain them at the end of season when winterizing. How do I check for water flow? Do I pull the plug & run the engine, or just pull it with engine off and see how much water drains. I have noticed during winterizing that some drain more water than others but never explored beyond that. Fwiw I have had the heat exchangers apart and found no sand or debris.

The discoloration is caused by heat. For some reason the back header tube is not getting the water flow it needs. You need to drain your headers more often than once a year. since it is the back header tube I would bet there is a blockage in the water distribution manifold under the header.

Changing your impeller/housing at least once a season? I change every 20-25 hours, minimum of once a season. Also have you done the header update for better (more efficient) cooling?

Toilet bowl cleaner will take the discoloration right off.

Impellers with housing changed each spring. Water pressure is good. I will start draining headers after next run this coming weekend. Does anyone know if this heat will or has compromised the header. I've read that leaks occur at the weld points and that heat contributes to weak weld points.

Also, what is the update for better header cooling. Does it apply to my settup?

I would also like to hear about the header update , first I've heard of it.

Eliminates the bypass
Header updatr.pdf