B series heat exchanger failure

[Roger bing]

When recently starting my motor, I noticed a decent amount of what looked like zinc discharged out my exhaust. This surprised me as I had replaced the zincs in December and the boat has seen very little use. Upon warming the engine and oil, I changed fluids as part of routine maintenance. This is when I noticed the expansion tank level was a bit low (330 hp b series). At the time I didn’t think much of it as I have not needed to add water to the motor in some time. Upon changing oil and fuel filters I topped the exp. tank and began to monitor the level. Two days later prior to starting the motor I checked the tank. Bone Dry. Turns out exchanger had coolant on sw side. At this point I figured the coolant had prematurely deteriorated the zinc. I replaced the exchanger.

Yesterday I noticed another shot of zinc out the exhaust again during startup. All fluid levels were normal. So I figured maybe the aftercooler zincs were shot as well. Turns out the bottom zinc was 95% gone. Now I started wondering, if my theory of the coolant eroding the zinc is valid how did coolant make its way all the way back from the exp tank to the lower end of aftercooler? It dosen’t seem feasible taking into account the height of each component, water seeking its own level, etc. etc.

Now I am left to believe my heat exchanger may have failed due to electrolysis based on the premature deterioration of the zincs. I plan on pulling the zincs on the other motor to see if they are equally worn. Has anyone ever witnessed coolant destroy a zinc before? In addition is there a test that can rule out electrolysis on the motor? In reading online I saw one where potential (voltage) is measured from the neg. terminal on battery to the fluid in exp. tank. Supposedly anything over .3V means there is significant stray current.

Topic

[Rob Schepis]

Eliminate the easy stuff – use a 110 tester on a twist lock adapter and test the dock tower. I keep this handy on the boat and whenever we are traveling I make it a habit of testing the tower before even bothering to drag out my cord….

[Roger bing]

Update! Think I’m on to Something

Rob, good call on that reference electrode. That thing is definitely somthing handy to have. I tested the boats hull potential and it is actually at the high end of the “protected” region. Turns out shore lead may be problem. Hull potential dropped from 1054mv to 930 mv when I plugged in. The book says anything 100mv or over will eat electrodes. Before notifying marina I tried to repeat the test and sure enough it came in at 1054 mv (which would be perfect). I jiggled the shore connection at the boat a bit and it jumped all over and settled down at 930mv. Going to retest tomorrow with a friends cord but it definitely looked promising. Also will leave boat unplugged for few days to see if zinc pieces stop exiting motor during initial startup.

[Roger bing]

Went down today… disconnected ground from battery… measured 1.8 miliamps of current with battery switches off. started disconnecting wire by wire.. got to the point where all sources were disconnected ( pos to starter, alt output, shorepower removed, etc.) There was not a source of power feeding this motor left connected. Yet it still read 1.8 ma between the coolant and battery ground.. only way I could get current to stop was to disconnect positive from battery as well.. other motor came in at 1.3 ma. I’m stumped.. only thing left is to move boat and retest to eliminate slip/marina as culprit..

Before I left I noticed what I posted in pics.. paint on exp tank was gone where coolant overflowed after filling.. other motors paint is still there. I guess I should test the ph? It’s brand new stuff I just changed upon installing new exchanger..

[Rob Schepis]

For sure any problematic equipment could be causing a current leakage so start there.

[Roger bing]

Hi rob thanks for the reply… I haven’t looked at running gear yet since boats only been in water for a month and waters way too cold to swim lol. I’ve already thought about the marina. I recently moved to bay shore and am no longer in Freeport..I never noticed uneven zinc wear between motors in Freeport. problem is the marina I’m in is mainly outboards… I’m literally the only inboard on my dock and I don’t think they worry about electrolysis as they pull motors up. Also I appear to be only boat that plugs in on my dock. I would imagine if the dock was “hot I would see it between both motors no?

After thinking last night I am wondering if my block heater may be an issue.. I think that is the side it does not work. I do not leave it on but perhaps there may be stray current coming in through the neutral …i will remove plug. And see what happens after testing for current.

[Rob Schepis]

Roger, is this new this season?
Freeport …. you must have quite a number of boats around you in close proximity… Anyone else right around you having similar issues?
Anything new since this started – change marinas or slips? Same marina but new shorepower electric work performed? New boat neighbors? New equipment added to your boat? etc etc. You see where I’m going..
I’ve used the Corrosion Reference Electrode from boatzincs and it’s a handy tool that comes with useful reference material. https://www.boatzincs.com/corrosion-reference-electrode-specs.html

[donald roth]

Your marina, or your boat, or Your neighbors boat may have an AC stray current issue that’s eating your zincs.
Have you looked at the zincs on your running gear?

[Roger bing]

Thanks for the feedback. Im not happy with the condition of the 3 week old pencil zinc in exchanger though. Somthings up. I will take look at water on start again and post once i know more.

[Tony Athens]

Sounds like typical soot on the water after after typical start-up.. Most engines do it , some more than others–Can be perfectly normal on the 6BTA 5.9…

[Roger bing]

After starting the engine I run to the back of the boat from the bridge. You can see the cloud that has dispersed into the water about a foot and a half from the transom. I look at the other exhaust and its not there. In it you can see little pebble like pieces that appear shiny. Unfortunately, the water in my marina is brown so its hard to see more to tell you exactly. I am going to pull sw feed to elbow off prior to startup and shoot it into bucket in a few days. Hopefully it will tell me more as to what exactly is going on.

[Tony Athens]

What exactly is a “shot of zinc” out the exhaust? No mixer I no of would allow anything thru it that could be seen? Plus, how could you “see” what is coming out the exhaust during a start up? Is the start key on the transom?

Something BIG is being left out here.

Tony

[Roger bing]

update with question

I serviced aftercoolers in the fall (early Dec.) and pressure tested. All is good. The aftercoolers are not the issue here. The engine is running fine no variation in top end RPM, stack temps, etc. I was simply noting the excessive, premature zinc wear when I checked the pencils after having the heat exchanger issue.

So its been a few weeks with a fresh pencil in the new exchanger. Every time the boat sits for four days or so I still get a shot of zinc out the exhaust on the first startup. Im pretty sure thats what it is as oil is clear with constant level and water level is same as other motor. Plus you can see little chunks sinking. I pulled the pencil yesterday and it was evident that motor must be alive with electrolysis. For three weeks it was suprising how much was gone.

Wanted to run my plan of attack by you guys and see what you thought. I always turn battery switches off when leaving the boat. The only DC that remains live is the bilge pumps which bypass the switches. Im figuring if I disconnect the ground wires (one to battery and other to second motor) from the lug on the engine and place a milliamp meter in series with the block/battery I should be able to read any stray current through the motor. From what I have read .3ma seems to be the threshold that constitutes a “hot” engine vs one that does not have stray current. If engine is ‘live’ I plan on disconnecting things till current drops and work backwards from there. Any advice is greatly appreciated before I dig in. Oh and last but not least, I plan on starting motor with sw hose disconnected from elbow and shooting in pail for few seconds to catch whatever is coming out of the elbow first for further inspection.

[Julian]

Pressure testing is a crucial part of aftercooler maintenance. When were your aftercoolers last serviced? It should have been done then.

[Roger bing]

Hi Tony:

As far as time, i am not sure. I am not the first owner of the motor. And the system has not been pressure tested. What would I be testing for it was pressure tested? The new exchanger is installed and fw side is holding water.
I was not suprised by the failure of the exhanger. I totally understand they fail from time to time. What Im more worried about is potential electrolysis. I change engine zincs routinely and never see them deteriorate that quickly. Going to pull them out of port motor today to see if they are as bad.

[Tony Athens]

Simple questions:

1) How many years has the heat-x been operating in salt water?

2) Have you pressure tested the system?

Post a few pics of the engine so I can see what you/we are dealing with..

Tony

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