Why metals corrode

[BodybyFisher]

I was looking for information on corrosion for bschelle and came across this. Its interesting to note that corrosion is relatively high for aluminum in this article and low for gold. I was looking for corrosion in relays, but this chart alarmed me when i thought about the NS engine. Has anyone ever heard of corrosion being accelerated by an electrical current or bad ground?, I vaguely recall something about that.

It seems to me that dampness is an issue if it infiltrates electrical contacts. Note the statement in this article "exposed to a humid environment"

Why do metals corrode by Corrosion Doctors

Here is a continuation of corrosion theory

Corrosion Theory by Corrosion Doctors

Everything you could want to know about corrosion

Corrosion Course by Corrosion Doctors

[Texas Jim]

I worked on seaplanes when I was in the Air Force. The HU16 Albatross. Was stationed in Florida. Whenever they landed them in the Gulf of Mexico or in the Atlantic... we had to wash them with a special soap to help neutralize the salt and rinse them with firehoses to get the soap and salt off of them.

The salt water would eat up the aluminum in no time if you didn't keep it clean. Has to go to a special school on corrosion to learn how to care for them properly. There was also a special paint we used on them called Zinc Chromate. I funny green color.

[95SevilleSLS]

They should design a gold engine...HA! That would be inexpensive!

[Cadillac Jim]

The head bolt problem is probably due to galvanic corrosion by traces of conductive coolant. That's a good reason not to push the 5-year limit for red antifreeze or the two-year limit for green.

I believe that the new head gaskets have seals around the head bolt holes, which the original head gaskets didn't. I would like to see some assurance in future designs of aluminum engines (just about all of them nowadays, not just the Northstar) that would keep coolant traces out of the head bolt holes, use non-corrosion-prone inserts for head bolts from the factory, and other design techniques to minimize this issue on very old engines.

[Ranger]

All head gaskets are designed to keep coolant out of the head bolts. This is nothing new. To do otherwise would be a guaranteed failure. Engineers know better. The more I hear about head gasket failure, the more I am convinced that the threads pull first. Probably due to casting problems or the head bolt coating wearing off in one small spot as the bolt is torqued or such. I still say blocks should be made of cast iron, the way God intended.

[JimD]

....I was looking for corrosion in relays, but this chart alarmed me when i thought about the NS engine.

You can bet the aluminum engine design teams are well informed on the matter of galvanic corrosion; and how to minimize the situation. You will recognize the writing style in this post...

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Re: Headgaskets - deterioration or pulled head studs?

There is always an issue of galvanic corrosion happening

when you have steel against aluminum. That has been

recognized for several decades...yes...LOL. That is why,

for instance, the Northstar headbolts have a special

coating on them, have the micro-encapsulated loctite

compound on the threads to lubricate/lock/seal the

threads and was the driving force behind putting each of

the Northstar head bolts into it's own, dry, sealed

chamber to keep any comtaminates or electrolytes away

from the aluminum/steel interface.

Magnesium and steel bolts are an even bigger issue. That

is why the mag cam covers are isolated with rubber

grommets so the bolts never even touch them.....

[Cadillac Jim]

Thanks, Ranger and JimD. I wonder what breaks down in this system, and why, when Northstar head bolt threads do corrode? If we knew that, and what to do about it, we could help a lot of people.

Actually, Galvanic corrosion has been recognized since Luigi Galvani made many of his discoveries regarding electricity. Note the many words derived from his name, such as Galvanized steel, which is tin plated steel that is resistant to corrosion. Alessandro Volta, who discovered the electric cell in 1800, first laid out the electrochemical series which laid out the first set of standard electrode potentials. In school, I was told that Volta first discovered the electrochemical effect by noting current between a zinc and a copper electrode on a dead fish at the beach, but I am unable to find any substantive reference to this colorful anecdote.

A common way of preventing corrosion on boats, particularly in salt water, is to use blocks of zinc bolted to the metal, so the zinc corrodes but the steel or aluminum does not. You see this on steel and aluminum hulls, parts of drive shafts exposed to salt water, bronze screws, and even in the bilge.

[JimD]

Thanks, Ranger and JimD. I wonder what breaks down in this system, and why, when Northstar head bolt threads do corrode? If we knew that, and what to do about it, we could help a lot of people.

Based on the headgasket horror stories I have read here and the other Cadillac board, I have convinced myself the first failure seems to be the depletion of the corrosion inhibitor package in the coolant mixture.

That leads to errosion of the gasket material.

In those cases where aluminum is present on the bolts at teardown, I have again convinced myself the gasket was erroded in such a way as to allow coolant (electrolyte) to enter the bolt area thereby accelerating the galvanic corrosion. Failed bolt hole threads would be the result of gasket failure; not the cause.

Coolant service, coolant service, coolant service; that's what owners need to know and understand and believe. And we have been singing that song forever.

I have no interest in cruising other auto boards so I'll add another question to the mix; is the Northstar the only aluminum engine that has a street reputation (undeserved as it is) for head gasket failures?

[Cadillac Jim]

My wife's 1999 Pontiac Grand Am with 3.4 l HO V6 suffered an intake manifold leak from the same cause. After I had my head gasket problem, I understood her antifreeze leak problem and had it fixed, and lo and behold, overage coolant had led to corrosion about the intake manifold. The mechanic said that it would have eventually led to leakage into the crankcase and brought down the main bearings...

[JimD]

....It seems to me that dampness is an issue if it infiltrates electrical contacts. Note the statement in this article "exposed to a humid environment"

High humidity and exposure to environmental liquids is easily managed with properly designed-manufactured-installed and maintained connection points. We have been doing this job on cars and boats and _______ for years and years.

Folks at or near sea level might see intermittent electrical problems that can be tracked down to connections that have higher levels of oxidation than you would find in a car in Amarillo, TX. Probable cause is salt water vapor intrusion.

In the case of relays and oxidation on the load switching contacts; relay design includes a very slight amount of scrubbing or wipeing action when the contacts are slammed into place by the relay coil. I have taken a number of failed relays apart and have not ever noted any ozidation at the load switching contacts. You will see evidence of arcing - but not oxidation or corrosion.

[BodybyFisher]

It makes you realize how good Dexcool really is give its recommended change cycle.

I must go back however. Has anyone ever heard about the acceleration of corrosion within the engine due to electrical problems causing electrolysis?

[Ranger]

Thanks, Ranger and JimD. I wonder what breaks down in this system, and why, when Northstar head bolt threads do corrode? If we knew that, and what to do about it, we could help a lot of people.

Based on the headgasket horror stories I have read here and the other Cadillac board, I have convinced myself the first failure seems to be the depletion of the corrosion inhibitor package in the coolant mixture.

That leads to errosion of the gasket material.

In those cases where aluminum is present on the bolts at teardown, I have again convinced myself the gasket was erroded in such a way as to allow coolant (electrolyte) to enter the bolt area thereby accelerating the galvanic corrosion. Failed bolt hole threads would be the result of gasket failure; not the cause.

Coolant service, coolant service, coolant service; that's what owners need to know and understand and believe. And we have been singing that song forever.

I have no interest in cruising other auto boards so I'll add another question to the mix; is the Northstar the only aluminum engine that has a street reputation (undeserved as it is) for head gasket failures?

Jim,

I have to respectfully disagree with you on this one. Think back to cast iron engines. How often did you hear of head gasket failures? Even with the old 2 yr coolant, which you know many people forgot about. Sure it happened, but not to the extent that we seem to hear about. Today we have longer lasting coolant and we are still seeing this problem. Many times from people who have maintained the cooling system. Sometimes even before the coolant is due for a change. To add to that, it does not seem to be as prevalent in other engines. How do we explain that? Perhaps it is GM's casting technique, or base material (didn't AJ once make mention of that?). Maybe the Northstar uses higher bolt torque than other engines? I don't know, but when it comes to the chicken or the egg, I am convinced that it is the thread failure that comes first allowing coolant into the threads and then the corrosion starts and the threads pull more allowing neighboring threaads to get coolant in them and the gaskets or cooling system service (or lack there of) get the blame. That's my theory and I'm stick'in to it.

[JohnnyG]

QUOTE (JimD @ Mar 3 2008, 11:28 AM)

QUOTE (Jims_97_ETC @ Mar 3 2008, 11:57 AM)

Thanks, Ranger and JimD. I wonder what breaks down in this system, and why, when Northstar head bolt threads do corrode? If we knew that, and what to do about it, we could help a lot of people.

Based on the headgasket horror stories I have read here and the other Cadillac board, I have convinced myself the first failure seems to be the depletion of the corrosion inhibitor package in the coolant mixture.

That leads to errosion of the gasket material.

In those cases where aluminum is present on the bolts at teardown, I have again convinced myself the gasket was erroded in such a way as to allow coolant (electrolyte) to enter the bolt area thereby accelerating the galvanic corrosion. Failed bolt hole threads would be the result of gasket failure; not the cause.

Coolant service, coolant service, coolant service; that's what owners need to know and understand and believe. And we have been singing that song forever.

I have no interest in cruising other auto boards so I'll add another question to the mix; is the Northstar the only aluminum engine that has a street reputation (undeserved as it is) for head gasket failures?

Jim,

I have to respectfully disagree with you on this one. Think back to cast iron engines. How often did you hear of head gasket failures? Even with the old 2 yr coolant, which you know many people forgot about. Sure it happened, but not to the extent that we seem to hear about. Today we have longer lasting coolant and we are still seeing this problem. Many times from people who have maintained the cooling system. Sometimes even before the coolant is due for a change. To add to that, it does not seem to be as prevalent in other engines. How do we explain that? Perhaps it is GM's casting technique, or base material (didn't AJ once make mention of that?). Maybe the Northstar uses higher bolt torque than other engines? I don't know, but when it comes to the chicken or the egg, I am convinced that it is the thread failure that comes first allowing coolant into the threads and then the corrosion starts and the threads pull more allowing neighboring threaads to get coolant in them and the gaskets or cooling system service (or lack there of) get the blame. That's my theory and I'm stick'in to it.

Ranger, you're point is moot. We are NOT dealing with cast iron engines, so forget it. Advancements in coolant technology is an ATTEMPT to limit the failure but obviously NOT the cure. What bothers me is that a simple SACRAFICIAL ANODE of magnesium might have been left out of the design of the Northstar aluminum engines.

I think you are correct in one sense, the gaskets fail first, but NOT due solely to corrosion from the cooling system, but flame corrosion from the combustion chamber, COMBINED with cooling system corrosion. Throw in a few other manufacturing tolerances and a little cold carbon rap and you have a recipe for failure. This is the weak area in the Northstar design, which was obviously recognized by the engineers. Why else would somebody go through a 4 step process just to protect the headbolts?

[Texas Jim]

I still say blocks should be made of cast iron, the way God intended.

Hear... Hear... I second that motion.

[Ranger]

I think advancements in coolant technology is geared more towards "maintenance free" than to fix a problem.

I realize we are not talking about cast iron engines. I was using them as a comparison.

I think you are correct in one sense, the gaskets fail first, but NOT due solely to corrosion from the cooling system, but flame corrosion from the combustion chamber,

Isn't there a fire ring around the chamber to prevent this? If this is the case, why don't all engines have failures? GM or their suppliers have been making head gaskets for long enough to know how to do it correctly by now, wouldn't you think. I mean this is not something new. I just have a hard time believing that all of a sudden we can't figure out how to make a head gasket that lasts. I still think it is a design or casting flaw.

Throw in a few other manufacturing tolerances and a little cold carbon rap and you have a recipe for failure.

Now you might be on to something there. Maybe THAT is the reason for the lowered compression ratio in 2000. Think about this scenario. Most Caddies are babied, thus they carbon up. Hence cold carbon rap and the bolt threads get pounded loose. Those that get driven hard don't suffer HG failure. Thus a high failure rate and no one can really make the connection because no one knows how the driver drives the car. When GM finally figures it out, they can't admit it for fear of class action law suits, so they lower the compression in the pretext of allowing the costumer to use regular fuel, thus giving the added clearance needed to the cylinder head. It seems so clear now.

[BodybyFisher]

You know, I asked the guru about that. Whether the cold carbon rap could 'push' the head off and contribute to the threads pulling... He seemed to thing that was insignificant, relative to the combustion, that the piston was 'rocking' in the cylinder not pushing the head up or off..

[Ranger]

Hmm, another valid point.

[Cadillac Jim]

I still say blocks should be made of cast iron, the way God intended.

Hear... Hear... I second that motion.

The way forward, in my opinion, is to solve the problems, not to retreat from them. But, that's probably just the engineer in me.

[JohnnyG]

Regardless of what you think the guru said, I think you are getting two completely seperate issues confused. Cold engine knock, prevelent in the 6.0L GM truck engines and others, including a couple of Ford products is caused by the piston rocking in the bore. The clearances on truck engines are a little "generous" in that department for a perfectly valid reason........and the piston skirts are terribly short to eliminate internal engine friction. But cold carbon rap is caused by carbon accumulations in the VERY UNIQUE design of the Northstar combustion chamber.

I'm still leaning toward CCR as being a contributing factor, even though I've heard the official rebuttal.

[BodybyFisher]

Regardless of what you think the guru said, I think you are getting two completely seperate issues confused. Cold engine knock, prevelent in the 6.0L GM truck engines and others, including a couple of Ford products is caused by the piston rocking in the bore. The clearances on truck engines are a little "generous" in that department for a perfectly valid reason........and the piston skirts are terribly short to eliminate internal engine friction. But cold carbon rap is caused by carbon accumulations in the VERY UNIQUE design of the Northstar combustion chamber.

I'm still leaning toward CCR as being a contributing factor, even though I've heard the official rebuttal.

Thanks Johnny

I think he was saying that when the piston hits the head because of carbon buildup, the piston rocks in its cyliner, and that the force is not transferred to the head, thereby pushing it up.. does that make sense?

What is CCR by the way, that acronym lost me, Thanks

[Ranger]

Mike,

CCR = Cold Carbon Rap.

I think he was saying that when the piston hit the head because of carbon buildup, the piston rocks in its cylinder, and that the force is not transferred to the head, thereby pushing it up.. does that make sense?

Actually that does make sense.

[BodybyFisher]

Thanks Ranger, I wish we could get the guru to chime in once in a while on his break.... He is sorely missed.

[Ranger]

That would be nice.

[Bill K]

As stated before, I had changed coolant well in advance of the 5 yr. 100K interval (74K / -4 yr.) Head bolts pulled & gasket failed. I knew about BBobs(aka guru) claim that the failures were the fault of the customers and not the mfgs. and wanted to be sure that I didnt fall into that category. Design changes in the bolts & pitch ect. lead me to believe that the coolant failure excuse was a knee jerk, "not my fault" or best guess, by the engineers, with the info available at the time, reaction.

A coolant change is important but I dont thing it is the root, or at least "only" cause of the head gaskst failure.

The only other car I ever had head gaskets fail on was a 1962 Buick Skylark V-8 with, surprise-surprise, an aluminum

engine block.

[BodybyFisher]

As stated before, I had changed coolant well in advance of the 5 yr. 100K interval (74K / -4 yr.) Head bolts pulled & gasket failed. I knew about BBobs(aka guru) claim that the failures were the fault of the customers and not the mfgs. and wanted to be sure that I didn't fall into that category. Design changes in the bolts & pitch ect. lead me to believe that the coolant failure excuse was a knee jerk, "not my fault" or best guess, by the engineers, with the info available at the time, reaction.

A coolant change is important but I dont thing it is the root, or at least "only" cause of the head gaskst failure.

The only other car I ever had head gaskets fail on was a 1962 Buick Skylark V-8 with, surprise-surprise, an aluminum

engine block.

I like this statement > with the info available at the time, that is an important consideration. I think you are correct, it results from a bunch of sources. I think that some of these engines got a mix of green and orange at some point also.

I myself am more educated now, I have done intake manifold gaskets on three 3400 GM engines, and the gasket was re-designed. I just heard of someone needing the intake manifold gaskets done a second time within 6 months! Both times by the dealer. By the way, I don't think the intake manifold gasket job is an easy job at all. GM has had problems with them and modified the torque specs also. So while I bleed GM, I know that ship happens. We have seen head gaskets go before 100K as happened to you. AJ brings up the idea that the aluminum can change becoming brittle and soft and with drilling and tapping the material the threads are bound to fail. That would explain why some time-serted engines fail anyway. It could also explain why the tech that does the time-serting at my local dealer has a negative opinion about it, and has said that it doesn't work. And I do know that techs have been known to do improper timeserting as KHE found in his engine. Is this caused by a chemical change, a breakdown for some reason, a bad casting?, who knows.

What I don't understand is how do problems elude the engineer and why do they release potential problems to the market. What happened to the days that they actually raced and did endurance testing? While its impressive that the NS is run for 300 hours straight at the red line, I think that the engine should be run hard till it breaks over and over and over, it should be driven to 100K miles over and over and over. ANYTHING that breaks needs redesign. It seems that GM is doing that....but WE are the testers, look at how the NS has improved from 93 till the current offering?, and NOW, stupidly they are moving away from the NS, I understand. Such a shame, develop, move toward dependability and perfection and then DISCONTINUE IT... Reputation and dependability to me, HEAVILY outweighs the bean counter's cost cutting. The first owner is not where you reputation goes down the toilet, its the subsequent owners that run into the problem that end up badmouthing the engine to death that KILLS your reputation. As someone else mentioned, I want to find out what other aluminum engines are experiencing. Honestly I don't hear these problems on other engines. Is this the inherent design? The alloy? The casting process? CCR as Johnny believes (and that I surmised at one point).

About 20 years ago, a friend of mine told me that he read that one day engines would be made out of ceramic.. What do we think of that?, can you put threads in ceramic?