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Old 12-19-2005, 08:40 PM   #1
jcutsh
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Caution corrision theory inside ***

A long, long time ago in this far away land of CF, I posted a question about a Daewoo with a severe water in oil problem.

Well the problem has been solved.

Behind the water pump, which is mounted in a machined hole in the front of the engine block, is a plug screwed into the main engine high pressure oil galley. This galley actually leads to the center hole in the oil filter.

The plug, a simple 1/4 inch pipe plug was almost eaten totally away.

Daewoo states: : “The plug was destroyed due to the corrosive properties of the antifreeze”

Now, I am not the brightest pigeon flying around the neighborhood, BUT, I do like to think for myself once in a while, especially after I have exercised by pulling the engine out of my car three or four times. I love searching for logical answers.

I know that companies that produce antifreeze go to great lengths to control the corrosive properties of their products, and that antifreeze comes into contact with la arge variety of different metals with very little damage. It is hard to imagine, antifreeze could eat up an iron plug in just 60000 miles.

My questions for all the guys with high Sat scores:

1. Was this damage due to chemical corrosion because of the antifreeze, or due to a cathodic problem, caused by the pH differences between the water and oil on each side of the plug, which turned the little plug into a sacrificial lamb? I have never measured the difference in pH between antifreeze and oil, but it would take very little to set up a metal eating electron flow.

2. Would a plug made of an inert metal, such as stainless steel be a permanent fix?

3. Aren’t they still teaching “cathodic protection” in our universities?

4. This plug sets right in the middle of the vortex of the water pump, making this the lowest pressure point in the entire cooling system (I believe). Could fluid flow and pressure, at this point, have caused a problem?

Go get em CF peoples. Learn me something.
Inquiring minds want to know.
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Old 12-19-2005, 09:05 PM   #2
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I don't recall your original post on the subject, but;

1. Anti-freeze is blended specifically to provide corrosion resistance. I don't know what Daewoo was talking about when they made that statement, but I'd be willing to bet at best it was poor wording and at worst it was technical tap dancing.

2. Stainless steel or brass certainly won't corrode as quickly as an iron plug will, and would be a good way to go. On the other hand, any kind of plug not made in Korea might have twice the original life expectancy as well.

3. Now you're getting above my pay grade. My knowledge of cathodic protection centers completely around the anode rod in my water heaters.

4. Possibly. Coolant flow patterns, air pockets and cavitation can and do cause accelerated and isolated erosion within cooling systems.
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Old 12-19-2005, 10:08 PM   #3
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jcutsh your query and VWHobo's response exposes two very important issues:

there are a lot of Korean built tankers plying the seas;
does anyone ever replace the sacrificial anodes in hotwater tanks?

I would suggest the plug corroded because of oxygen release from cavitation. You should be able to identify this by looking for rust and fissures. Electrolysis will result in a smooth pitting. Straight up cavitation damage should be evidenced by pitting on the pump diffuser plate and volute.

I use impressed current cathodic protection on water vessels, but also have the end caps nylon coated.
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Last edited by Wally : 12-19-2005 at 10:10 PM.
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Old 12-19-2005, 11:49 PM   #4
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Well Wally

Gaseous release is something I thought about, but since we are talking about a closed system, I would thing the constant heating and cooling would drive any excess gases from the fluid and make release of any gas almost impossible. Perhaps, graphitization could be part of the answer.

Many water distribution systems use cathodic protection for their pipelines and towers, where they have two sources of water, such as two water plants or wells combined. Anytime two different pH waters meet, it eats the pipe.

All outboard motors and stern drives have sacrificial electrodes to prevent destruction .

But of course, Hobo could be right. You can’t make a plug out of silly putty.
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Old 12-19-2005, 11:56 PM   #5
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Of course, now that I think about it, Wally. That plug came from Holden, some place called "way down under". lol
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Old 12-20-2005, 12:01 AM   #6
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Jcutsh!!!


I joined after you left, but your legacy stays behind. Welcome back, man!
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Old 12-20-2005, 12:02 AM   #7
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I wasn't going to say anything, but yes the motors are made here and loaded into Hyundai's, Vectras, etc around the world. Be very afraid if you have a GM, Alpha, Saab, etc with an Alloytech V6 too
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