linderpat wrote: ↑Sun Sep 12, 2021 11:26 am
As I pointed out previously, that was never a question raised by me, or my point. Obviously head gaskets are a wear item and need to be replaced over time. I am not a total idiot (soome would argue this of course
)
I think the 'conversation' is getting muddled by conflating head gasket deterioration and head pitting.
linderpat wrote: ↑Sun Sep 12, 2021 11:26 am
My point - and for one more time to be stellar clear - is that I have questions about the incidence and seriousness of the pitting of the heads from coolant seepage around the gaskets in every case on a low mileage car (or any mileage for that matter).
I understand this - that you are skeptical that every single 928 has deadly head corrosion. That's fine. I've never written that.
What I have written is that it is 'time' to replace head gaskets fleet wide because:
a) for early cars can we expect head gaskets to last for 40 years?
b) for later cars we know - strongly suspect at least - that their heads are more prone to expensive-to-fix corrosion.
linderpat wrote: ↑Sun Sep 12, 2021 11:26 am
That is being painted as the newest most serious issue confronting us, and make the cars a lot less desirable.
This I don't understand. Either knowledge is good. Or knowledge is bad. Or you do not believe what is being posted?
Or you believe that this is some unique-to-928's issue?
From talking with 'my guy' that does reconstructive work on everything from my client's heads, to Ferrari cylinder blocks, to one-of-one parts for Bugattis, deterioration of "plain" aluminum castings is not at all unique.
linderpat wrote: ↑Sun Sep 12, 2021 11:26 am
Now that has been clarified on rennlist that it is an issue mostly associated with the 87+ engines. My point is that one cannot make a blanket statement about it - the condition, which obviously exists in certain cases (I've seen the pictures too), is dependent on a number of factors including maintanence history and coolant used, etc.
Again, the only unqualified blanket statement I've made is that head gaskets cannot be expected to have a design lifetime in excess of 30 years.
The corrosion damage is a separate, but related issue.
linderpat wrote: ↑Sun Sep 12, 2021 11:26 am
If you and Greg are saying none of that matters, and that pitting will occur no matter what, then I would not touch a post 86 car and never recommend to anyone to buy one. They are ticking time bombs in need of replacement engines, and that is an unacceptable defect. I have a hard time believing that this state of affairs is actually the case. I have seen pictures of blocks where no pitting has occurred under circumstances where one would have expected it.
I've never made such statements vis-à-vis corrosion and you are applying a too-broad brush. First don't conflate block corrosion with head corrosion. Next realize that the 'time bomb' issue has two manifestations and that head corrosion is actually the least serious manifestation.
A deteriorated or 'popped' head gasket can damage the cylinder block.
Serious head corrosion just makes the heads more expensive to repair...
... unless the head corrosion is allowed to proceed to the point where the manifestation is just like a 'popped' head gasket.
I advocate head gasket replacement for the early cars for the first reason and for later cars for the second reason.
My many discussions with 'my guy' along with the TOS threads have brought me to the opinions I hold and have posted.
In particular:
- the later heads (90+) are more porous than the earlier heads. It is the porosity of the castings that makes the later heads more expensive to repair and ALSO what causes them to exhibit far more deterioration due to crevice corrosion when coolant is allowed to 'go bad.'
- ensuring that the additive package in the coolant is refreshed on schedule will limit corrosion.
- nothing we do will enable head gaskets to last indefinitely.
- a 928 engine 'marinating' in old coolant without being operated will exhibit less deterioration than a 928 with old coolant that is circulated due to once-per-month "warming up the fluids" operation. (All other things equal.)
- and last but not least, very few 928s that arrive at my shop come with since-new records that enable an educated guess as to the health of head decks (for '87+ where head deck health rather than gasket age is the concern.)
I have seen a set of garage-queen low mileage GTS heads with insufficient corrosion to warrant the expense of 'decking.' But, those heads came with records of on-schedule coolant changes, or long periods of dormancy immediately followed by a coolant change.
And of course, there's the '89 that *sat* for 14 years with the same coolant that required no welding.
A mid-mileage '91 with 20 years of records and no coolant flushes that was 'warmed up' once a month that required significant welding.
All the 32v heads I have seen with my own eyes exhibit head health consistent with the bullet points above to the extent of records (or previous owner stories) provided.
SeanR wrote: ↑Sun Sep 12, 2021 12:21 pm
Personal experience on head gaskets, the 1990+ cars are the worst.
The 90+ heads suck because of the casting porosity. 'my guy' has done enough heads for me now, that this is a hill I'll die on.
SeanR wrote: ↑Sun Sep 12, 2021 12:21 pm
I don't know if they used a different material on the gaskets but everyone I've had to tear down required welding on the heads because of it. Most are low mile examples that just sat. Took down an '80 Euro with 100k on it a couple months ago and while the gaskets were 40 years old, they looked pretty damn good, and that's usually what I find on the early cars.
I'm not sure exactly why, but what you wrote above and/or exactly the way you wrote it, make a mental gear turn in my head.
How many places in PET (or at least old PET) do we see "gasket" and on the next line down "gasket (without asbestos)?"
I did a few minutes of googling...
In 1987 the US passed a law required all automotive stuff to be asbestos-free. No doubt this came after Europe did the same thing.
Asbestos was used in automotive gaskets.
Was it ever used in 928 head gaskets? If so, when did it stop?
If 928s stopped using head gaskets with asbestos in MY'87, or '88, or '89, would that further explain why we see 16v head gaskets that look better than 10-year younger 32v head gaskets?
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