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Date:         Sun, 5 Apr 1998 14:53:42 -0300
Reply-To:     Tim Smith <smitht@UNB.CA>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Tim Smith <smitht@UNB.CA>
Subject:      head leaks/stats etc.
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset="us-ascii"

snipped from digest/ErikO post

>From the corrosion I've seen personally, I see no indication that the >coolant/water combination or grounding issues are the cause of this >problem, rather just signs of it. It is only under the headgasket >sealing surface where this problem is isolated. There are other places

Bingo, it is a simple liquid-solid/galvanic corrosion problem, specifically called 'crevice corrosion' due to coolant squeezing under the gasket and sitting against the head. That's why you see that 1/2" wide track of pits around the entire sealing area. Stats may be interesting, lot of variables at play here, including what level the heads were torqued down to, what sort/number of daily temperature cycles is the whole engine seeing, ambient temps., what age of gaskets, coolant mixture ratio and 'freshness'. I think the scatter in the survey will be huge, reliability low.

I'd be willing to bet that most leaks occur during late winter/spring, since very cold/cooled-off engines reduce sealing pressure and allow seepage. This happens more in winter (plus stiffer rubber), and a flow path ('join the pits') is more likely to get established due to the large expansion/contraction motion. Once a few drips appear, BarsLeak can still seal them, I think this has been established, but allowing them to keep dripping means the coolant starts to clear out the flow path and accelerate leak rate.

>you should find corrosion if the problem was one of the two above >causes. The whole head would corrode for that matter. That fact that >it's isolated under a surface that is supposed to be sealed makes me >think of other options.

ditto, I'm not a holistic mechanic, can only comprehend small things completely, so keep it simple pls. bye, Tim


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