6BTA 5.9 370 hp #6 cylinder hot, injector or valve? Causing exhaust leak.

[Kevin Battjes]

After noticing an exhaust smell in the cabin and engine room, a soap bubble check indicated an exhaust leak around the metal-to-fiberglass joint on the port engine exhaust riser. On the way to haul out with a warmed up engine at no wake speeds, checking in the engine room looked normal, but smelled of exhaust, at higher RPM (1500) the port engine exhaust riser was smoking at the metal/glass joint region, either charring fiberglass, exhaust leak, or both. Checking the exhaust ports on the head-to-manifold joint with an IR thermometer showed cylinders 1-5 at 185-200 F or so, but #6 was at 400 F or more while running at 1500 RPM. At idle RPM the exhaust ports are all similar around 185-200 F. I suspect that high of exhaust temp has scorched the fiberglass joint on the riser leading to the exhaust leak. Turbo does not seem to be damaged, but has not been closely inspected. Water injection is well below the bend in the riser so I don’t suspect water intrusion (or should I?). Both engines have the SeaBoard Envirovents, V-drive type.

I talked with a local Cummins mechanic and he asked if a thumping sound was heard. Answer is no. He thinks it is the #6 injector. I expected to hear there is a burned or leaky exhaust valve to make that kind of heat, but I am not a mechanic (but learning more every day about them). I don’t really doubt his opinion, but have not worked with them either.

The port engine does use about 10% more fuel than starboard (which seems to be running normal). It is also slower to accelerate than the starboard, but that may be unrelated.

The question is: Would a malfunctioning injector cause the high exhaust heat at that cylinder at higher RPM? I am looking into having the injectors pulled and tested and likely have a compression test. Does this approach sound reasonable?

Photos are attached of the riser. Leak is at the bottom and around the pyrometer port. I will have to have some repair/rebuild work on the riser, but need to get the hot exhaust port fixed first.

The paint on the turbo outlet is peeled and looks a little baked from the heat, but the rest of it looks fairly normal.

Any suggestions? Thoughts?

Topic

[Justin Riege]

There is a simple explanation why number 6 is hotter. All of the exhaust gasses from all of the other cylinders have to pass that point and funnel through the opening for the turbo right there. So that area tends to have a more heat.

That doesn’t mean there isn’t some other issue present. I would definitely start with Tony’s suggestions of checking that gasket and dry side of the exhaust for leaks. Like tony said, the peeling paint is not a cause for concern. The dry side of the exhaust is hot. By the looks of the rust, that paint has been peeled for a while.

[Kevin Battjes]

Thanks Tony. I’ll be pulling the riser while in storage and follow your plan. Very low clearance at the top of the riser so it may be a tight fit for the soft wrap. See attached.

The question about the injector would be why does only #6 cylinder get much hotter than the others measured on the head at the exhaust port where it bolts up to the manifold? Seems like it should be close to the other cylinder temperatures. Valve leak or injector?

[Tony Athens]

My thoughts.

1)———-You have a gasket leak between the riser flange the the turbo. Remove the riser. Block sand the turbo face until it’s clean. New hardware with anti-seize on the threads and use a graphite gasket..

2) ———–And OR, you have a crack in a weld that you cannot see (under the hard fiberglass heat wrap) ??———–If that is the case, then throw out the hard wrap ( you have to cut if off) , fix the riser and use a new soft wrap made by ATP in Irvine Calif.. Maybe $500..

I do not buy the injector thing, and all the burning “paint thing” is normal.. Buy a small SS brush and get rid of it.. ..

Tony

[Kevin Battjes]

The boat is not equipped with boost or EGT gauges. Pretty much the factory set-up 2000 model year Tiara 3500 Express, engines built in 1999, just over 400 hours. The aftercoolers were serviced in early 2017 using the kits and following the method from Seaboard. Heat exchangers serviced at the same time. Both pressure tested to assure no leaks. Temps on the starboard side consistent around the 185-200 F under the conditions observed. Typical cruise speed is 2500-2600 RPM, for about 24-26 mph depending on load and sea conditions. I had been thinking the exhaust smell was from station wagon effect until it got stronger and more persistent. The boat is used strictly in fresh water.

[Corey Schmidt]

Are you monitoring BOOST and/or EGT numbers on either of these engines?

When was the last time the aftercoolers were serviced PROPERLY?

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