Heat exchanger vs. pencil zinc. Assumptions and questions

[bgary]

Today was maintenance day... oil change, check the transmission fluid, etc. And then change the pencil zinc in the heat exchanger. Normally a 3-minute job, 2-1/2 of which is spent digging out the 9/16" wrench.

.... and then to find that only part of the pencil zinc came out with the bronze cap.

Arrrgghhh!

I can feel the rest of it in the hole. It's solidly stuck in place. No way that I can think of to get it out. I tried for the better part of two hours. By taking off the end-cap closest to the hole, I can see it... but nothing I tried would persuade it to move, let alone come out. (I didn't want to get too energetic with it for fear it would break loose and move out of reach)

My assumptions at this point, are two:
-- it's probably a pressing problem, as it likely isn't doing much galvanic good in there right now, and
-- it's probably not a good idea to run the motor until it is fixed. If it breaks free in there, not sure where it would go.

So, it looks like my next chore is going to be pulling the heat exchanger. So much for a 3-minute job.

Couple of questions, since I've never done this before

1) It seems pretty clear that the process will involve draining the coolant from the system, disconnecting the 4 hoses, and unbolting the bracket that holds it in place. Anything else I should plan for?

2) Once I've got it out, seems like a good time to have it boiled out. My guess (just from looking through the end cap) is that the zinc is being held in place by accumulated crud, so it's probably past time. I've heard (?) I could take it to a radiator shop and have it cleaned out. Is there a better way?

3) This is an (apparently) original 2" diameter unit. Once it's out... should I think about replacing it with a 3" diameter heat exchanger? I've heard people have done that, but don't know the pros and cons. Or where to get one. Or what to ask for. It occurs to me that the end-cap gaskets should probably be replaced, the port one at least is looking pretty tired. That might be harder to find than a whole new unit, don't know.

4) looking forward to that happy day when all is back together, anything I need to do (other than refilling coolant and such) before firing up the diesel? I've heard about people having high-temp issues resulting from air-bubbles in the system, are there ways to prevent that?

6), oh, and how often do people generally change the pencil zincs? I've been doing it each spring, have never had a problem until today, but I'm wondering if doing it more frequently would help the system stay healthier. Or at least make it so the next one comes out whole.

At this point, I'm frustrated and feel like I don't know what I don't know, any insights appreciated....

Bruce

 

[Christian Williams]

My current engine ran for years with several entire zincs caught in the Hx. They still work even broken off.

If you can tie up the hoses that connect to the heat exchanger, you may lose only a little coolant. There's no real need to drain the entire system, unless you feel like it.

Next time I will boil the unit out myself, as I have in the past using muriatic acid. I think I'll switch to the "Barnacle Buster" product linked to in the comments on this blog entry. The end gaskets are available at West Marine, $3 each or so. I made my own with a pair of scissors out of some nitrile rubber I had lying around.

I'm familiar with the move toward a 3" heat exchanger on the 32-3, but to my mind if there's no overheating issue I wonder why it's necessary.

 

[Frank Langer]

Hi,
I replace the pencil zinc every 5 months, to avoid it getting too thin/weak and snapping off. They are cheap and it's an easy job. Replace any coolant with diesel coolant, not just any automotive coolant, as the diesel is specially formulated to avoid problems caused by non diesel coolant. There is more detail on this issue in a recent related thread.
In my opinion the coolant should be replaced every few years, so if this hasn't been done now would be a good time.
I have had good success having the heat exchanger serviced by a local radiator shop every three years - - cleaned out, tested for leaks, new gaskets, painted. Previously when I left it for five years, they warned me it was getting pretty bad.
The hardest part of this job is removing the hoses from the heat exchanger, which requires patience, a hose remover tool or flat screw driver, or cutting them off if you have enough hose to reconnect them.
You may need to bleed out air bubbles by leaving the cap off the highest point in the system after you restart the engine, but keep an eye on it so it doesn't boil over as the coolant expands with heat.
Good luck with it!
Frank

 

[Kenneth K]

The pencil zinc corrosion/erosion always seems to be worst at the base where it screws into the housing. To offset this, I've been painting that lower 1/4" of the new zincs with nail polish before installing. It doesn't corrode under the nail polish.

5-6 months between replacements is about what I've been doing.

 

[kiwisailor]

Run Barancle Buster through the raw water system it will dissolve the zinc away as well as all the other scale, best to let the stuff sit 12hrs then flush out with raw water and then install the new zinc.

 

[Bolo]

Regular boat maintenance often turns into “teachable moments” and this is another example. It’s like our boats are trying to get us to learn something new about them. Back in 2018 I had the opportunity to learn many new things about my boat when the transmission went bad (long story) and in turn required me to move and refurbish my heat exchanger. You can read about it here:
Post in thread 'Transmission Problems...again. - The Saga Continues'
https://ericsonyachts.org/ie/thread...ms-again-the-saga-continues.15738/post-115389

When I had to move the HX because of the install of a new transmission (again, read the story to find out why) I decided to recondition it. I had used CLR (available at the local hardware store) to clear calcium buildups and water stains in other non-marine applications in the past. So I tried it on my HX and it worked great. I’m sure having it boiled out by a radiator shop is maybe the best way to go but CLR worked for me too. I purchased new end caps and gaskets and repainted the HX red mostly because I had a can of red paint in my shop already. If you do paint cover the nipples on the HX where the hoses connect So they don’t get painted. You want a bare metal surface where the hose connects. And speaking of hoses, I replaced them all. Although my pencil zinc was never stuck I found a small pile of zincs when I took the end cap off. As for going to a 3” HX I never saw the need since the 2” never overheated on me. Actually changing my old Sherwood raw water pump to an Oberdorfer seem to give the engine more “cooling power”. If you have a water heater connected to the plumbing then there should be a bleed valve located near the top of the engine on a hose that goes to the heater. This is the valve that you use to bleed air out of for the cooling system if you have to replace some or all of the coolant. When I refurbished the HX I drained all of the coolant and replaced with new fluid since it hadn’t been done in awhile. I got a heat spike soon after start the engine but resolved it by opening the bleed valve to the water heater.

 

[1911tex]

ok guys, I give up...where do I find the location for the pencil zinc on the heat exchanger...Universal M25 5421?

 

[Christian Williams]

...

 

[1911tex]

View attachment 39362...View attachment 39363

Thanks Christian...swore I was looking at it without knowing what I was looking at.....the heat exchanger is 10 months old....sooooo...it's about that time!

 

[nquigley]

Unless you know the correct size, you might want to order a couple different lengths. The first one I ordered was too long - it seemed to jamb against the central structure before the cap screwed all the way in. I had to get a slightly shorter one. I probably could have hacksawed off a 1/4" but didn't.

 

[Rocinante33]

I always must hacksaw the end off of my zinc before installation. Last time I didn't cut off quite enough and because of interference, I thought I had stripped threads. Arrrgh! wasted a lot of time needlessly, futsing with it. Hours! It just needed to be cut shorter!

As to the original problem, Bruce, try to use either a cheapo corkscrew to get that piece of zinc out or try a small, sharp tipped probe. The zinc has softened (that's why it broke off) and you can get the corkscrew or probe stuck into it and perhaps you can pull it out. Maybe try to partially straighten or elongate the corkscrew tip with pliers to allow it to get inside and poke the zinc. It's worth a try.

 

[Christian Williams]

The busted zinc should be lying next to the end cap (which is the only place it can penetrate). If the end cap is accessible, that's the easiest way to get it out.

 

[markvone]

3) This is an (apparently) original 2" diameter unit. Once it's out... should I think about replacing it with a 3" diameter heat exchanger? I've heard people have done that, but don't know the pros and cons. Or where to get one. Or what to ask for. It occurs to me that the end-cap gaskets should probably be replaced, the port one at least is looking pretty tired. That might be harder to find than a whole new unit, don't know.

Bruce,

You probably don't need a 3" HE in the PNW. My boat with a 5424 lived happily in Santa Barbara with a 2". I didn't have cooling issues until summer in the Chesapeake with 90+ degree water. That said, if you do buy new, get a 3" (don't know if you can get a 2" any more).

299835CN Universal Heat Exchanger

Overview 299835CN Universal Heat Exchanger Offered is our replacement for the 299835CN Universal Heat Exchanger. Sentence here. Some details to note: 299835 and 299835CN are the same part for us, both with a Copper Nickel Bundle. If you have a Universal M25XP, XPA or XPB, you’ll need...

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The only Con is the cost. The engine won't care, it has a thermostat

The Pro is more cooling. More reserve cooling as the HE fouls or adequate cooling in hot water if the boat ever moves to a hot water climate.

Mark

 

[Second Star]

Lucky guys! My Universal M18 OE heat exchanger has the zinc end cap braised in place. Spend lots of quality time shaking the pieces out the zinc fitting hole.....

 

[Kenneth K]

2" heat exchanger pencil zinc with nail polish painted base....

 

[bgary]

2" heat exchanger pencil zinc with nail polish painted base....

OK, I have the threaded fitting scrubbed out and the carcass of the old pencil shoved far enough out of the way that I can get a new one in. It's trapped in a chamber between the end-cap and a perforated interior bulkhead, so it can't go anywhere and I don't see how it could impede water flow.

I also bought some clear nail-polish today. I was ready to sternly rebuke anyone in line who challenged my lifestyle choices

@Kenneth K when you say the bottom 1/4", do you extend that past the corner toward the threaded area? I'm thinking of doing the bottom 1/4" plus the top thread or two, just to ensure there's no erosion where the threads meet the body - seems like that would be the worst area to create a weak spot....

 

[Rocinante33]

I think that painting any part of the threads will be a bad idea. For the zinc to truly be sacrificial, you must ensure electrical continuity which happens through those threads so bare metal to metal contact is best.

what say you all?

 

[Kenneth K]

Yeah Bruce, that's pretty much what I do. Like Keith said, you wouldn't want to cover all the threads (one year I mistakenly put Teflon tape on the brass fitting) but I can't believe the miniscule galvanic current needs much contact area, so covering the first thread shouldn't make any difference.

 

[bgary]

I don't want to brag (OK, well, I kinda do), but... for the first time in the Modern Olympic Era, I was able to get an old pencil-zinc out of the heat-exchanger in one piece.

Many thanks to @Kenneth K for the nail polish trick. It worked a treat and based on the appearance of the old zinc it clearly didn't impair the galvanic purpose of the zinc itself.

 

[Prairie Schooner]

This spring, after an hour an a half of futzing around I got the broken zinc out. No removable end cap. My elite coat hanger tool helped. I was so elated I felt like I'd picked the lock on Fort Knox. My inclination has been to blame the well-intentioned good-natured motorcycle mechanic training as a diesel mechanic who installed it. But, maybe that's just what happens with them. Next spring I'm trying the nail polish trick. Makes sense to me. (I did trim down the new zinc after this photo. Probably would not thought to cut it if I hadn't read about that on EYo.)