I have 4 hrs on my new 540 efi, two week ago I found black on my white swim platform that is directly below my port exhaust tip. I pulled the plugs thinking it was running rich, but plugs looked perfect.

Went back to the water only to immediately burn through the boot between the header and tip. I brought it home, pulled the Outdrive and put a new seal kit in after finding a damaged o ring. I ran the boat for 20 min around table rock lake and burnt through another boot.

I have back flushed every hose and cooler on the cooling system, and checked the veins on the sea pump only to find nothing. I tried tightening my serpentine belt, and took the boat out. Upon startup the port side starts shooting water out about 3 sec later than starboard, but have the same amount of flow at idle. But, with the boat on plane for a cpl mi, port side flow is next to nothing, and the tailpipe reads 50deg hotter than starboard.

The bottom rails are plumbed to the thermostat housing w 1" hose, the thermostat is 140deg with 3-1/8" holes in it. Thermostat housing's two ports are semetrically forward, 90deg apart, with 2 other temp probes in it. The motor always runs at 150deg. I am obviously overlooking something, but still don't understand why I'm running out of water only on the port side header while at cruise.

Are theses E-tops headers new or previously used units? Do they use clamp on tips or are they the newer once piece units?

Almost sounds like you have some debris in the port header or rails that is moving with higher pressure and water flow and causing a blockage to flow when cruising at higher rpms.

Have you checked the water pressure on the system at cruise rpms?

Best Regards,
Ray @ Raylar

I just put clear hoses on both sides, the starboard side is immediately running full, the port had an air pocket until I raised rpm's to 1000.

He headers were used, and have a v-band clamp to connect the header to the tailpipe. And a 4" rubber boot hose that connects the tailpipe to the tip. They were check at Ateco when he built the motor 4 engine hrs ago.

What is the best way to clear the header or any debris from the header?
Thanks for your help, Brock

I would disconnect the collector to tip u bend haose on each header and trhe watrer rail entrance hose on each header and hook a hose up tot the coolector outlet hose fitting on each header one side at a time and put hose pressure backwards in thre header on each side and see if there is an obvious flow difference port versus starboard. This should tell you if the port header water passages are clogged more trhan the starboard header and isolate if the problem is in the header. take both header tips off if that does not point to anything and check erach tip seperatly for water flow from a hose. If these all check OK and pretrty much equal flows at a common pressure then your rraw water flow problem and exhaust tip hose burn through is not being caused by the header or tip but something else on the raw water flow and path.

Best Regards,
Ray @ Raylar

are the hoses long enough to switch port and starboad to see if other side heats up the same?

I have hooked a garden hose to both sides and it appeared to have equal flow. I reversed the hoses between the thermostat and headers and the port side still lost flow after we got on plane. I switched the hoses back but replaced the port side hose, and still had a reduced flow on the port side. So I guess I have some type of restriction in the header. Any suggestions now?

these are 1-piece exhausts? can't switch risers? take it off and take it to a radiator shop and get it flushed out. or try back-flushing it yourself if there is a way to hook a hose up to the water exit. also, quikie pressure test. fill water jackets and watch for water in the exhaust tubes. search this forum for "pressure test etop lights. onesickpantera had a cute way to do it.

Seems like a silly question, but have you looked inside the thermostat housing ? Some of the Mercury housings had a semi-blocking diverter piece which was developed to try to equalize flows to the exhausts in some 454-502 Mercruiser engines. Some of the stock and aftermarket thermostat housings had some spring loaded balls that acted as check valves and many would stick closed or partially closed and create such an issue.
If this is not an issue then it sounds like this used port header or tip may have some sort of blockage to flow that's creating you condition. When you flow them with a hose on the headers make sure you flow into a known bucket or barrel size on both headers for a specific time period the same on both headers and that way you can rreally compare the actual flow volume going thru each header at a specific pressure and flow rate.

Best Regards,
Ray @ Raylar

FYI, My headers are merc style elbow tops with welded distribution tubes and removable tailpipes, and my thermostat housing is aftermarket without any type of diverter plate or spring loaded by-pass balls.
I have removed the port header to forward flush, back flush, and pressure test, but found nothing that would cause this condition(flowed perfectly). I did notice that the internal flapper on my tip has the rubber seals burnt off of it. The flapper is able to turn 360 with some resistance. I am wandering if it is possible for this flapper to get bound up while on plane and causing enough back pressure into the tailpipe to dirasticly reduce water flow on the port side, but the motor still runs great.
I am out of ideas, but i am going to remove my flapper completely from the port tip, and rebuild my sea pump, and see if this fixes my problem. If problem is resolved I will get flapper seals ordered asap. Otherwise the boat is going to either Ateco Engines, or Performance Boat Centers.
Thanks for your ideas and help!

make sure its not sucking air anywhere, I had one motor running 50 degrees hotter than the other, water flow seemed equal on both engines, turned out that the plug to the flush out was cross threaded, replaced the plug and no problem