I knew after a few of these all had the same issue in mere weeks to a few months that it needed changing, but time and motivation got away on me.
Finally got around to blasting, lapping and a few spot repairs to pitting to the genuine original with epoxy. I found this on the S after only 1 year and 5 months of installing a brand spanking new KC thermostat housing. Brand new 8 year long life Penrite coolant too.
What shit are these made from? Every single one has done this in rapid time, some in just a few weeks as it did on my VR.
The metal was even blistered and lifting in one spot, popped like a blister and was filled with the same green gooy hydroxide looking stuff inside.
Also note how much the bolt heads sunk in, it's like it's made of cheese I only torque these to 25Nm too, not the 35 max allowed.
Never has an issue with the genuine ones.
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So now the repaired original is back on.
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I'd like to know if the cooling system was full. That type of corrosive buildup usually occurs when air gets in. The bolt issue may be due to the use of spring washers machining the surface when you undo the bolts.
Yes, it was totally air free. This happens only with these KC castings aftermarket housing for some reason I think is related to it's metallurgy. The alloy is very very soft, can whittle it with a blade like it's made of a hard lead alloy.
If you take note of the gasket each side, the manifold side remained clean and indeed, the manifold surface was still nice, but on the housing side it's putrid, which shows it is something with the metal itself.
I have only ever seen that type of buildup when the component has been exposed to air for some time. The gasket sides is a bit of a mystery and the housing got wet by coolant or there is an issue with the gasket material and the housing alloy which I have never seen before. Did you use sealant on both sides of the gasket? OEM housing is probably impossible to find now and were subject to the aftermarket blackmail prices.
You can get genuine housing as NOS on ebay and facecrap occasionally. Gasket is a genuine one and they are meant to be installed dry. I haven't had issues with the genuine housing and a fresh genuine Holden gasket, Aftermarket gaskets aren't so great and tend to weep slowly through the core of the material itself.
All my other cars where I used the genuine housing and new genuine gasket have been toally fine for a few years now, no leaks at all, edges of the gaskets are as dry as the day I installed them.
The KC casting ones weep within 1 to 2 days 100% of the time due to being too soft and squishing out of shape. Then the metal does that green goo thing anyway.
That's why I went back to the original housing once I had figured out the issue.
I’d be very vary of long life coolants. Penrite market one as being a HOAT but don’t list the glycol content.
For me I’d stick to a coolant that has a decent glycol content as its been proven for decades, and avoid OAT coolants unless absolutely necessary.
Theirs HOAT is more than 60% for the concentrate, OAT is superior for corrosion protection, but is generally incompatible with copper and brass, but other mixed metals like alloy, iron and stainless it is better than the old type A.
HOAT is a good step above the old stuff as it still retains copper compatibility but gives better modern protection that also lasts longer.
I've had zero issues with the HOAT on the genuine housings and the engine in general. I also found the intake manifold to do wonders on HOAT where as conventional does show some trace evidence of erosion over time even when changed on time (normally 2 years).
That said, I had the same issue with the KC housing on my VR which ran the old conventional 3 year green penrite before they started the HOAT green. That was back in 2014, I replaced it in 2017 and again in 2024 and it was severely eaten away, other alloy parts including the stainless heater insert pipe to timing cover hole is in mint condition (this has high galvanic corrosion potential) . I popped open the hoses and opening to have a look. All perfect, so it was all isolated to the KC part. I lapped about 1mm off to bring up a decent surface in late 2024 but I sold the car late last year with the engine out early 2025, it was eaten away again, only on that housing as always.
One of the cars had conventional Nulon, it suffered the same issue with the KC part. Ever since changing each car back to a genuine one, the issues all went away one car at a time. Logic and process of elimination makes it without a doubt the issue squarely on the housing material.
I know a guy personally who I talk all things Buick for a few years now and has driven the same VR ute for 25 years he switched to the OAT red coolant many years ago and reported that even the thermostat gaskets now never leak or weep, and upon changing a thermostat found they have zero additional corrosion compared to the green Nulon he normally used before.
For anyone that has pulled apart modern mixed metal engines running factory OAT knows how ridiculously pristine they are in the cooling system, so I firmly believe that the coolant isn't the issue, after all, OAT and HOAT are best at alloy above all metals, over all other older coolant chemistry.
Perhaps KC use some alloy mix that is not compatible with coolants in general. It really looks and feels like some soft alloy, very shiny and bright like a polished part, but it's not polished, according to google AI search, it says it's likely 1100 series alloy or one of the 1000 series which is almost pure aluminium. So perhaps maybe the very alkalinity of the coolant itself is reacting with the very pure aluminium? Penrite say it's a PH of 8.7 which is right in the ideal rage for protection, so I'm not sure about that. It also suggests that this alloy could be able to corrode even in a inhibited coolant if the temps are above 80c which is interesting to read, but the car was seldom run, not that I found use or non use had any difference in this case, just time + KC housing.
Holden and nearly all car makers use a high zinc alloy, typically die cast for thermostat housing and many similar parts, that's what give it that dark silvery colour. It makes the alloy very rigid and hard, perfect for this application and cheaper to make for die cast parts. It also it ideal for corrosion protection. So to me, it's very much the wrong alloy choice. I'd say it's because 1100 alloy is much easier to cast and work with, easy to cut, drill, machine,and linish etc...
I think the high zink is that if the system gets neglected they work as a sacrificial anode. Cheap and easy to replace rather than some obscure part or a cylinder head like the Falcons.
Oh a side quest regarding coolants and what not, I have found some info about an inhibitor used in OAT and HOAT coolants for a long time, called 2-EHA (2-Ethylhexanoic acid), which is an excellent inhibitor, but has the downside of being in somewhat incompatible with silicone rubber and potentially attacks nylon.
Sounds familiar? intake gaskets! A few pages back I posted the ones from my shitbox when I replaced the heads, they were totally stuffed after only 4 years and that ran on Nulon green, and for a short period prior Tectalloy. I thought the exhaust gases were the main factor, but upon learning of 2-EHA I now have doubts on what the main cause and think back to all the times I had these fail without a real definitive answer. Given the 2-EHA has been standard across nearly all brands for a good decade or so, this main help explain why really old low K engines that hadn't been touched since the early 00 or older, ones that were neglected in every sense, seemed to have gaskets in way better condition that ones replaced much more recently and with good service history/
I have confirmed the Nulon has it and had it at the time I filled it. Older penrite list it on their green 350k coolant as recommended for these engines.
The newer 8-12 year ones do not list it, but neither does it list anything other than ethylene glycol and the bittering agent, all other non hazardous chemicals are not specified, so I guess they do not need to disclose all ingredients. But in only data sheets, they listed nearly everything. 2-EHA is considered hazardous, so maybe they are 2-EHA free now.
So I emailed Penrite to clarify this. My understanding is most manufactures are moving away from 2-EHA for not only health and environmental reasons, but also because of the silicone elastomer and nylon issues it's known for.
Penrite informed me that all of their green coolant products contain 2-EHA as well as the 10 10ths racing inhibitor and the classic coolant.
So I gather 2-EHA is very wide spread and the old IAT (inorganic additive technology) that predominately used a silicate inhibitor are quite uncommon now and have all but been replaced with a HOAT which is a mixture of inorganic and organic inhibitors.
So a bit more digging into it and which coolants are 2-EHA free and mixed metal and material free comes out to be current Euro coolants, normally purple or blue (purple for sure).
These use a Silicon-OAT and Phosphate-OAT mix hybrid that does not use 2-EHA, but somewhere between what a lot of Asian cars use which is a P-HOAT from what I recall reading, and the Si-HOAT is a bit like the old silicate IAT tech, but I guess attached to an organic acid molecule other than something like 2-EHA.
Euro coolant specs must be 2-EHA free as most Euro engines use plastic and silicone elastomer seals and gaskets and many Euro engines have mixed metals like cast iron, alloy, stainless. Brass is also listed as compatible in mixed metals.
So from what I can gather from all the info and research I've done, the Euro purple coolant may well be the right one to suit the Holden V6 as it has materials much like a Euro engine, especially a compact turbo diesel which are very wide spread over in the Euro market.
The down side is these coolants have less life than the HOAT green and probably the reds. But still 8 years long life, the green is now rated as 12 years.
I never really let my coolant go past much over 3 years anyway.
I did ask in a response if I could potentially use the purple in place at my own risk, but based on that info available from their very own product data and spec sheets. I should hopefully get something on Monday.
Another thing is any coolant that uses a silicate based additive, when the coolant is old and beyond spec, the compounds break down at some point allowing for silicate to precipitate out as micro sized crystals and they are abrasive, this can cause the water pump seal to wear out much faster and fail.
I often saw something like this in the early to mid 00s on all non alloytec Holdens of the time and I think this is likely what the problem was. Probably coolants used the older silicate tech and people were pushing past that 2 year replacement period. Silicate additives are super good and offer very quick protection on bare metal surfaces, but they deplete unlike newer HOAT and OAT tech, so when the coolants are older the 2 years (back then), they could have well precipitated out and kills the pumps.
I only torque these to 25Nm too, not the 35 max allowed.