Ok, first run of the season, not terrible but could have been better. Ended up with this nice rainbow on the center engine, #1 cylinder water jacket, obviously not getting enough water. Water pump & pressure were all ok, on the starboard header, all pipes are cool, on this header, the other three pipes cool and the engine temp is normal. My suspicion is that the heat exchanger could have some blockage that is partially constricting water flow and since the #1 pipe is the tallest and hardest to fill, it is being starved. I removed the end caps on the heat exchanger and did not see anything obvious but its hard to see through all of those tubes that are the size of a straw. My next step was to take a piece of thick wire and run it down every single one of those tubes to make sure it's clear, but that is not very appealing. Any other tricks or suggestions??




Ok, first run of the season, not terrible but could have been better. Ended up with this nice rainbow on the center engine, #1 cylinder water jacket, obviously not getting enough water. Water pump & pressure all ok, starboard header - all pipes

Just curious...Have you done the header update that removes the bypass? The update will help increase the flow to the tubes.

Yes, 4 years ago. I am now suspicious of a bad injector causing it to run lean and hot. All of the three other pipes are cool. Everything else in the raw water pathway seems fine except this one tube and I've definitively ruled out a problem with the header itself. If that #1 cylinder was running that hot, it would explain the bluing. Going to pull the plugs next.

gasket seals at the heat exchanger end caps need to be inspected -- they cause issues for restrictions. common problem for all heat exchanges.

Compression testing - and how well does the engine run ? could you reach WOT with that engine ? - Hand held temp gun at each runner from the head to the collector to compare temps -- also temp the spark plugs while running and compare. Engine coolant temp is ?

Water output testing to compare water volume and flow.

Fuel injector issue - cylinder running lean.

Possible valve issue or the start of one

Fuel pressure readings ??

I'm interested to see the plug for that cylinder. I'd probably borrow/steal a borescope from someone to peep around in the cylinder too.

Now that I'm thinking about it, I noticed the following. Usually, when all three sticks are in the same spot, the center engine typically lags about 200 RPM from the two outer engines, ie. I have to nudge the stick a bit forward to get RPM to be all the same. On this last run, I noticed the center engine running about 100-200 RPM faster than the other two when the sticks were even.

I think it a lot easier than that. I think all you have is a blockage in the water distribution manifold under the header. You have blocked water flow to the hot pipe.
The headers are going to fill to the same level even if there is no flow - so all of the pipes would have the same amount of water in them. And I can't believe a lean cylinder would create enough heat over a normal one to burn off the water in that pipe. I have had this happen before. If one of the hoses gets full of sand it will burn the paint off that tube.

I've already ruled that out. There is no blockage in the header at all.