FredR

I have a corrosion issue on the thermostat housing nozzle external surfaces where the coolant hose slips over the boss- just wondered if this is a "common" occurrence- thoughts?

The housing on my engine will probably have to be replaced shortly [assuming such is readily available].

belgiumbarry

i think it's very common. Never seen a "old" engine that had not any corrosion on the bosses under the hoses.
Those are wet "dead" places ( no fresh flow ) , were aggressive chemicals can grow in % and start corrosion.
New coolant and/or flush the engine will hardly reach those places.

GregBBRD

Somewhat common.

Although I hesitate to go there.....it's more so on cars that have had the incorrect coolant or have not had the coolant changed at regular intervals.

Jim Devine

Just get it clean, down to undisturbed metal (wire brush, etc) and put a thin smear of JB WELD on the pits & sand to round with a fine paper when it's cured- the hose & clamp should make up the difference

Petza914

When I took my 79 apart this summer I found the same thing as well as on the coolant connection near #4, which was much worse. Cleaned up the other one, but replaced this one.

FredR

Gents,

Many thanks for the inputs- pretty much confirms my expectations. I also have a problem with the Y piece that also was corroding from the outside in underneath the hose.

Of the four possible corrosion mechanisms I can think of it cannot be:
1. General weight loss corrosion- no corrrosion on the inside of the piece.
2. Galvanic corrosion- there is only one electrode.
3. Pitting corrosion- there is no pitting within the main body of the thermostat housing.

Anyone care to hazard a guess as to what type of corrosion mechanism is taking place on the external surface of the nozzle underneath the hose?

thepurpleblob

I just attacked mine with a wire brush in a drill. An acceptable result was achieved.

hacker-pschorr

FYI the majority of the wire brushes you find at the local store are carbon steel, which is a no-no when working on aluminum or stainless steel:

https://www.spiralbrushes.com/brush-...-wire-brushes/

I have a box of various sizes of stainless brushes specifically for anything aluminum. Once they touch regular steel, they are ruined for aluminum or stainless work. Could be a minor thing, but stainless brushes are readily available and not expensive so why chance it?

thepurpleblob

I think I used a brass brush. However, I didn't know that. I'll get some stainless steel ones.

FredR

For the examples you have seen demonstrate issues of this nature did you happen to observe whether they were examples with higher mileage or lower mileage - or maybe no obvious correlation?

dr bob

At the risk of adding fuel to a similar fire... This kind of corrosion is not so different from the corrosion discussed in the 'never again G05 thread' https://rennlist.com/forums/928-foru...y-forever.html. A somewhat 'dead' area, exposed to coolant but with no circulation. Old coolant with lower-pH contaminants get to work on the metal at their leisure. It might be a Good Idea to remove those hoses/connections at every coolant change, clean and flush the surfaces to remove deposits and contaminants, etc. How often? Mine get done every belt change (7 years or so) in the front, twice that for the rest when all the coolant and heater hoses are swapped.

This all makes a good case for powdercoating some of the the semi-wetted parts exposed to coolant. There's also a growing case for getting stainless replacement Y-pipes into production. More than plenty of those are corroded beyond the cosmetic. At least they are grounded while installed.

uraniummetallurgist

Hi All:
Aluminum alloys corrodes in many ways as discussed elsewhere on this site. The video below give a good overview of the various mechanisms (speaker's voice is pretty soft in some places). Of interest in the video are the preventive measures that can be taken to protect the aluminum alloy. Anodizing, painting, powder coating or any other method to prevent surface wetting are effective ways to minimize corrosion.



All the best,


Joe

FredR

Jim,

I took a similar approach in terms of cleaning it up but I coated the pitted surfaces with vaseline and clamped the hose as close to the lip as possible. To date it has held for 3 years and I will shortly be removing the assembly as and when I replace the coolant in the near future. It will be interesting to see how it has progressed.

I noted your use of the term "pits"- this is very significant in terms of understanding what is going on.

FredR

Barry,

You wrote a nice "lay description" of what is going on. It is not a really severe issue in this location given my example is now close to 30 year old but annoying nonetheless when one understands what is really going on.

FredR

Hi Bob,
Apologies that despite education on the subject matter I have not as yet been able to get the multi quote feature working as intended. So will respond with some thoughts on a point by point basis as enumerated:

1. Good to see "some lights" coming on here- I am confident you will be "fully enlightened" in due course.
2. I suspect that the problem here has been exaggerated by the designers building flared sections into the design on the premise of helping to secure a fluid seal. The clamp is invariably tightened further along the hose and that leaves a crevice [oops I really meant to say gap] between the hose and the base metal. My Y-piece was knawed away from the outside to inwards direction and had penetrated through in places. Three years ago on the last coolant change I cut the flared section off that was corroded, smeared the residual section with RTV and tightened the hose over the goo. Three years on not a drop of coolant has been lost. I will shortly be changing the coolant if the pH is "marginal" and for sure will inspect to see whether corrosion has been stopped in its tracks [or not]. The boss on the thermostat housing was well corroded around the flared section but clean as a whistle where the camp came down on the hose
3. The perception of aged coolant is [I suspect] "technically" flawed albeit the general intent implied is understood. I will explain this observation in due course but it should be obvious that aged coolant is not causing this issue as the problem is not generally manifesting itself across the vastly greater coolant exposed surfaces. The best that can be said is that if the coolant condition is borderline the problem will manifest itself "quicker".
4. Powder coating the external surfaces may well have prevented this corrosion issue. Another approach might have been to eliminate the flares and clamp directly above the tube entry into the hose- 15 psig is not difficult to seal against. For the thermostat nozzle a machined external finish with a nominal push fit interference in the hose might have been a better approach. I do not consider this a major problem given the life span seen on my motor but I will hazard guess and suggest that well used examples fare much worse in terms of chronological life.
5. Stainless steel is probably a big "No no". Given my hypothesis is correct passivated metals are the biggest victims of such attacks and once the passivated coating is breached corrosion is assured- just a question of how long it lasts rather than whether it will last. It would be interesting to know what the stock y-piece is made of. I assume it is a mild steel coated with something like zinc. Whatever it is, once the passivated coating is breached the steel underneath is fair game.
6. It would be interesting to know if anyone has actually experienced an in-service failure of either the thermostat housing or the Y-piece. I have a feeling many will have been replaced when the damage was spotted but I suspect non will have actually pissed out coolant- if anyone has seen or experienced a coolant shower at such locations please holler.
7. Not sure I understand the relevance of "grounding"- perhaps you can explain the context you have in mind. The thermostat housing is clearly grounded through the block or so I would think but as I can reason it does not help or hinder anything.