Diesel Slick in Exhaust 6CTA8.3 480 CE

[Jerome Ciliento]

Can anyone help me identify the cause of a small amount of diesel slick coming out of the SB engine.  I have a 2006 express Luhrs with twin 6CTA8.3 480 CE’s with only 710 hours.  I have had the fuel tanks polished and the fuel filters are all new.  The SB engine has recently started bouncing about 10 rpms up and down at idle when cold and level out after a few minutes.  It also hunts around 1200 RPM and levels out after that.  I have not had the valves adjusted and being the third owner of only 4 months I have had the entire cooling system flushed and new aftercoolers installed by certified local Cummins service company along with the air intakes cleaned and serviced.  The engines run at 163-165 degrees and all the vitals are text book per the displays and gauges.  The local Cummins people speculate that an injector may be leaking too much fuel at idle and this is creating the slight slick behind the boat.  I haven’t had them out to test it yet but wanted to get some insight before I did.  This engine has always steamed quite a bit more the Port side but I don’t think that this is a related issue but thought it would be worth mentioning.  If anyone has insight about more steam on one engine vs. the other engine your input would be appreciated for that as well.

 

Topic

[Rob Schepis]

Steam (continued)

Coolant temperature and exhaust temperature are two different animals so the fact that the two engine’s coolant temps are the same does not speak to why the visible exhaust steam differs between the two engines.

The max temp you should get measuring the wet (cooled) exhaust is 140degF, less is better.  Measure the port and starboard and measure around the circumference as perhaps one showerhead is doing a better job of spray and mixing the water to the hot gases, for example is the top hot and the bottom cool?  Probably need to shoot these at different rpms.  The better the mix the cooler the wet exhaust becomes and the more steam that is condensed.  If something is noticeable here one of the mixers could have clogging.

The hose between the seacock and the pumps (the suction side), is that a wire hose?  Could they be failing internally?  Age?  Is the hose to the steaming engine pump routed with more bends than the less steaming engine.  The more bends = more stress = more likely internal hose failure.

Do you have squid screens (aka south bay strainers, aka wedge strainers) under the boat.  Have they been fully cleaned and inspected?  Are they the “positive flow” type where the holes are drilled on an angle?  If the screen was removed and reinstalled in the wrong orientation that would decrease flow considerably.

New impellers is good.  Was attention paid to the pump cams and wear plates as well?  The pump should have test ports where you can test for reduced pressure or high vacuum.

[Jerome Ciliento]

Rob, All of the raw coolers were taken out, the aftercoolers were replaced.  All the other coolers were also cleaned and serviced along with new impellers and new hoses including the intake hose from the thru hull.  It doesn’t make much sense that I am maintaining 163-165 degrees but one engine makes double the steam than the other.  Should I throw a temp gun at the exhaust elbow and see if there is a temp diff there?

[Rob Schepis]

Steam

Increase in Steam is usually related to decrease in raw water flow.  You mentioned some recent cooling system work, was that on the raw water side?  You didn’t mention the raw water pumps?

But you’ve only owned the boat 4 months, right?  So you don’t really know if this is an “increase” or an inherent condition that could be related to the characteristics of that engine’s raw water loop starting from the thru-hull and all the way back to the exhaust mixer ..

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