CAT Heat Exchanger Zinc bonding

Discussion in 'Diesel Engines/Drives/Transmissions/Props' started by ttmott, May 9, 2014.

  1. ttmott

    ttmott PhD in OCD GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    Changing the engine zincs, its that time of the year, and it dawned on me that the heat exchanger caps the zincs thread into are composit (plastic). How then are the zinc rods bonded to the metallic components of the engine and boat? They won't do any good unless bonded.... Are there wires or bonding straps inside of the plastic?
  2. trit21

    trit21 Active Member

    Dec 16, 2007
    Live, Orlando: Boat, Ft. Pierce
    See signature
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    So your saying the threads that the brass nut screws into is plastic and does not touch any metal at all? Sorry for my ignorance but not familiar with Cats.
  3. ttmott

    ttmott PhD in OCD GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    That is what it appears - there seems to be a metallic insert in the plastic cap that the zinc assembly threads into. Is that insert bonded somehow to the engine? That's the question....
  4. Turtlesboat

    Turtlesboat Minister of Media TECHNICAL Contributor

    Feb 4, 2007
    New York City
    1996 450DA, TNT, Caribe dink w/15hp OB.
    3126 427HP TD transmissions
    Yes, there's a metal sleeve inside that mates to the heat exchanger when it's bolted on.
  5. Alex F

    Alex F Well-Known Member

    Nov 14, 2006
    East Coast
    2005 420DB with AB 11 DLX Tender, Raymarine Dual E120 MFD/Radar/XMWeather, ST7001 A/P, AIS, SeaLift
    T-Cummins 450Cs Straight-Drives, 9KW Onan Generator, 40HP Yamaha for tender.
    I'm bringing this old thread back to life, as my friend with 3126s has the same puzzle. The fact is that the HE zincs go into plastic HE cap and pretty much don't do anything corrosion preventive, as there's no metal to metal contact between the zinc and the HE. When the zincs are taken out during regular maintenance (say every 6-12 months), they just have discoloration, but 90-95% of the zinc remains intact, which means it doesn't work as it should to protect the engine.

    The original HEs are 17-18 years old and work just fine and we believe that it's just due to the overall engine bonding system. However, the question is, are we observing a design flow in regards to zinc-to-engine bonding or is there something that were missing here in regards to how CAT designed this? I get it that the HE housing is making the contact with the engine via metal bracket that's welded onto HE, but having the zinc being screwed into plastic cap just makes no sense.

    If anyone can shed some light on this, I'd greatly appreciate it.
  6. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    There is no design flaw. A metal sleeve is cast into the heat exchanger where the anode threads into the HE cap. That sleeve extends to one or more of the 4 bolt holes that attach the cap to the HE body so when everything id installed and buttoned up, there is metal to metal contact between both end caps and the HE body.

    Here is the only photo I can find of the inside of the end cap; note the star design on the cast in sleeve at the bottom:

    This design is also why you never use Loctite or over tighten the zinc plugs when changing the zincs. It is a $250 screw up if you break the sleeve loose in the end cap.
    The Bill Collector likes this.
  7. JVM225

    JVM225 Well-Known Member GOLD Sponsor

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    My Cat dealer recommends Loctite 51147 Copper Based Anti Seize for the threads on the zinc caps.
    Amazon has it for 13.75 with free shipping.

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