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Old 04-15-2016, 10:06 PM   #1
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sacrificial anode and engine part damage

Can one of the local armchair metalurgist diagnose what is going on with the the bottom cover on this heat exchanger?

That bolt-thing is actually a pencil zinc.

I dont like the look of that...

I'b better start trying to find a replacement cover and stop that degradation.
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Old 04-15-2016, 10:23 PM   #2
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Salt capillary migration through a fibrous gasket ?
do a taste test .
Whats dose the anode look like have you taken it out and inspected it ?
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Old 04-15-2016, 10:40 PM   #3
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Greetings,
Mr. CLA. I tend to agree with Mr. g. Take off the plate, clean it up well while checking the mating surfaces of both the plate and the exchanger body for pitting. Couple of coats of good paint on the plate, inside and out (looks to be cast iron so POR15 would be a good coating), new gasket with maybe some gasket goo and you should be good to go. Ah, put in a new anode while you're at it.
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Old 04-15-2016, 11:01 PM   #4
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A very old friend who since passed away here in Australia built Blaxland putt putt motors all his life from an apprentice till over 90 . He would always soak a fibrous gasket in hot differential oil for a day before he used it . I have carried on with this and after 4 year it seemed to have worked so I will continue doing so.
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Old 04-16-2016, 10:38 AM   #5
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The cover itself looks like it should be removed and bead blasted, primed and painted.
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Old 04-16-2016, 11:23 AM   #6
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Is it because the anode, being embedded in the cap, and perhaps no electrical connection between the cap and the cooling jacket, is why only the cap is deteriorating?

Is the extra charge trying to escape right off the cap which is why over the years its blown off the paint from the cap?

Is it because the anode - over the years has not been adequate (or changed often enough) such that the cap is trying to do the job of the anode?
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Old 04-16-2016, 11:46 AM   #7
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Is it because the anode, being embedded in the cap, and perhaps no electrical connection between the cap and the cooling jacket, is why only the cap is deteriorating?
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No, water travels down. That's why the lid and not the upper part is rusted. If the assembly were upside down what is now the upper part would have the trouble.

Once paint has been breached water/rust will penetrate further and further. I have seen rust runners travel a long ways under otherwise solid looking paint. The rust was not YET bad enough to bubble the paint.

Be carefull when trying to remove the cover as the bolts may be rusting and be difficult to remove. A broken bolt will be trouble. Try it, wiggle back and forth often to beak up the grip, soak with penetrating fluid. Upside down won't be easy but some cotton batting taped into place should hold a reservoir.

Most likely GASTON, Post #2 nailed it. This has been going on a long time for that level of salt residue and rust. You may not see it but not only salt residue but actual water has been coming through. Not much water but enough with the salt to rust the part and knock off the paint.

The zinc WILL NOT help or hinder that external corrosion. It is meant to protect the internal parts where the actual zinc is immersed in water.

As suggested remove it, BLAST it and repaint. I agree about the Por15.
But even so if the water continues to escape the rust will eventually return.

Take care with the gasket. I have seen gaskets that were sealed well initially take a set over a period of time and then seep. The set allows bolt sealing/clamping tension to be lost Snug the screws again. Use some Nev R Seez or similar on the screws so they don't rust/corrode into place in the future..
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Old 04-16-2016, 11:56 AM   #8
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ah ha! And gravity is the culprit! Salt moisture went down not up... got it... easy fix pending finding a replacement gasket... or the gasket goo
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Old 04-17-2016, 08:31 AM   #9
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Use SS bolts.
Depending on your skill level, I might use permatex ultra copper gasket maker instead of a gasket. good to 700*F
I know it would work for me. It may not work for others.
POR15 is good, but if it does not leak, all you need is primer and paint after cleaning off the rust.

I like KG Gun Kote, hard baked on coating wont rust. Look it up.
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Old 04-17-2016, 10:25 AM   #10
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Do not use stainless bolts. It is an aluminum casting and the SS bolts in al form a more reactive galvanic cell if the threads get wet. The SS bolts won't corrode, but the expensive al casting will. Just use the same alloy bolts and coat threads with grease.

The white stuff is corrosion product from the al corroding. If there is contact with the bronze cap and the joint is damp, you have an active galvanic cell and the al will get pitted.

No fan of al housing heat exchangers for this reason.

Periodic disassembly, cleaning, resealing and greasing tends to slow the corrosion.
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Old 04-17-2016, 12:09 PM   #11
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If aluminum then yeah I suppose SS is not so great. All my outdrives were built with SS bolts. But they can get stuck. If anti seized-greased and well sealed, then why not.
I have asked around for aluminum bolts before and none seem to have such things. And they would be weak too. Maybe bronze bolts better, but also easier to buy SS.

SS would be loads better than carbon steel.
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Old 04-17-2016, 07:55 PM   #12
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SS would be loads better than carbon steel.
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NOT SO. SS is weaker than the usual Gr 5 bolt material used. SS can do some funny [not] corrosion tricks where a steel bolt will simply rust giving warning of an impending problem.

Not saying not to use it but do not just assume that SS is better in applications like this.
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Old 04-18-2016, 07:50 AM   #13
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SS would be loads better than carbon steel.
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NOT SO. SS is weaker than the usual Gr 5 bolt material used. SS can do some funny [not] corrosion tricks where a steel bolt will simply rust giving warning of an impending problem.

Not saying not to use it but do not just assume that SS is better in applications like this.
Ok, go ahead and be contrary. Ask yourself why outdrive OEM use SS bolts.
I have had not too much trouble with SS and aluminum. I have rebuilt-repaired a few sterndrives. And if those bolts had been carbon steel and not SS, then they would have long ago been wasted into piles of rust.
A little heat, sometimes a lot, and some rust buster and hammer whacking gets those SS bolts out of old aluminum drives. The main problem is the aluminum swells up because of corrosion gripping the bolt tight.

It seems to me, a coating of permatex gasket maker and greasing the bolts will seal the water away from the bolts way better than a porous gasket material which will soak up salt water. that water will wick right into the bolt threads especially with heating and cooling cycles.
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Old 04-18-2016, 08:33 AM   #14
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Outdrives have to use SS as they are submerged in seawater. Not a good analogy. Take a look at marine diesels, which are what we are discussing: How many use SS bolts on their aluminum case heat exchangers?
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Old 04-18-2016, 10:06 AM   #15
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Outdrives have to use SS as they are submerged in seawater. Not a good analogy. Take a look at marine diesels, which are what we are discussing: How many use SS bolts on their aluminum case heat exchangers?
It really is not a poor analogy, these bolts in aluminum are exposed as well to salt water if the gasket is porous.
It is the price of the bolt since plain steel works ok or OEM would not use them that is the tripping point here, not the applicability of the SS bolt strength. Maybe I just like SS bolts.
I have had problem with plain steel bolts on exhaust manifolds and elsewhere when exposed to corrosive fluids,. the heads erode, sometimes they rust, they get weak, they break coming out. I am not inexperienced, experiencing many bolt failure over decades of wrenching, I just switch to SS where I feel it is better. I don't take well to automatic rejection of something just because someone says 'we don't do it that way', I am not stubborn, I yield to what I think is just plain better.
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Old 04-18-2016, 10:09 AM   #16
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For years I have been reading recomendations for using Tef Gel on SS bolts or screws into Aluminum. It's pretty expensive, I've never tried it yet. One day I'll get around to buying a 2 oz "tub" for $38.00
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Old 04-18-2016, 10:21 AM   #17
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For years I have been reading recomendations for using Tef Gel on SS bolts or screws into Aluminum. It's pretty expensive, I've never tried it yet. One day I'll get around to buying a 2 oz "tub" for $38.00
Might use Rectorseal T plus 2 on bolts instead. Stuff is not easy to remove even with soap and water. I just use grease or a silicon gasket maker, depends on what I think would be better depending on the situation.

This here job, I might use permatex black or ultra copper etc... and grease the bolts.
I have been working with KG Gun Kote which is a bake on phenolic resin coating impervious to acids, water, gasoline, etc... on various parts including cast iron. I have found acid etching to clean off rust using muriatic on cast iron pieces seems sufficient for KG Gun Kote to stick well, versus grit blasting with AlOX 125 grit media. I bought some for another purpose and using it other things now. I am going to test it on some metal carb fuel bowls next. I would likely Gun Kote and bake several coats on that cast cover piece too. Gun Kote will seal the metal, so if it is porous, it will no longer leak. I suppose epoxy coating would work also.
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Old 04-19-2016, 12:15 AM   #18
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I'm not being contrary and I had no way of determining your expertise. I simply intended a note of caution. Too many people simply assume that SS is better in all things and it is not and I have had that conversation.
I also am aware of the use of SS in o/b engines and outdrives.
If you feel comfortable with using them here then go ahead which is actually part of what I said.
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