GregBBRD

Actually, I'm not trying to creating hysteria, but simply pointing out reality.

......Low mileage 928's, which missed routine maintenance during some period of their lifetime (very likely), are way more prone to have acidic coolant damage than higher mileage examples, which received routine maintenance .

And, if someone is going to lay out 150K...or even 50K for a "perfect" low mileage example of these wonderful cars, they should be informed enough to know about and think about the potential issues.

The low mileage 928 that was for sale on BAT had almost every detail listed, with over 130 pictures. Perfect car, right? Any details about coolant change intervals? How about simply removing the thermostat housing and taking a single picture of both it and the inside of the water crossover?

Without more information:
Into the purchase price, one needs to add in the reality that most '88's on the planet have severely compromised head gaskets (just from age and normal "marinating").
And unless a seller has specific records of coolant services, plan on there being corrosion (of various levels...possibly traumatic.)
Add in the known issue of '88 heads cracking (which can occur when '87/'88 heads are retorqued) and some of the "luster" of that beautiful, low mileage example fades a bit.

Reality is a far different "master" than hysteria!

drooman

Anyone seriously considered remanufacturing the heads? I'm sure it's an economics equation. ... GTO Engineering makes new Ferrari 250 heads, head spinning expensive, but the cars are valuable enough to justify the costs. Countless companies make new small block chevy heads, even the chinese make them and they are cheap! but the gazillions of customers must be what make that economic equation work.

Are 32v 928s even getting close to the value that justifies this endeavor? I'll bet a few people in this conversation have considered it.

@worf.. I always suspected some very low grade electrolysis is what blows up the gaskets/ heads in the 32v cars. Also wonder if 968 heads do all this baloney...if they do not why don't they?

FredR

I have explained in quite some detail previously that the cylinder head corrosion is brought about by a relatively unknown corrosion phenomena known as crevice corrosion. In every case that has been catalogued on this forum the evidence was crystal clear that there was no problem with the condition of the coolant and the problem centres about what happens to the coolant when it is trapped in a stagnant layer between the gasket and the cylinder head in the areas outboard of the fire ring and inboard of the gasket sealing beads. The problem centers around the fact that at some temperature around 55C when the chemical package gets exhausted the pH changes from alkali to acidic and when the pH drops to about 4 things start to go pear shaped. Once the trapped liquid changes like this it sets up an electrochemical potential difference and when there is a common electrode - in this case the cylinder head - electrons flow in just the same way as they do in a battery and as I can tell, once it starts it does not stop and this is why the damage can be so destructive. In a way it is similar to galvanic corrosion but the difference is galvanic corrosion has two electrodes and one electrolyte whereas crevice corrosion is the other way round.

In a flanged joint if the metal surface damage shows pitting that is a 100% sure sign of a crevice corrosion attack having taken place. The only fault of the coolant is it happens to be a mix of ethylene glycol and water - the chemical protection package type and brand are totally irrelevant. If the main body of the coolant is spent it would simply make a bad situation worse. This problem can and does fester away for many years and only becomes apparent as and when something blows or the heads are routinely removed for whatever reason.

The really interesting question is "what triggers it"- I am still trying to work that mystery. My pet theory was that it happens more in cars that are left for months on end without being run and thus no thermal cycling as it were thus more prevalent in low milers. My S4 motor ran for 16 years until the car got totalled in 2005. When I pulled the heads everything was in perfect condition but then the car was run regularly- several times a week at least and sometimes daily. Three examples I saw over with head damage were all left for months on end without being used. Unfortunately Jim's example kind of killed this theory as his freshly GB built example was well used and still had the early stages of this problem.

The 968 most certainly suffers from this problem as do some Corvettes and probably many more engine designs if we did but know it. I have never followed this up on the 944 platform and I am not familiar with that engine configuration. I dare say it may be similar. The root cause of the problem is [I suspect] the open deck configuration that leads to the gasket being designed the way it is. If Porsche knew this problem was going to happen they could have designed it out.

As GB stated earlier a simple look inside the thermostat housing will indicate whether the coolant has gone off if there are signs of a general corrosion attack. I have never seen a single example of this happening but I am sure it will have happened somewhere along the line.

The notion that the coolant has to be changed every two years by and large is generally speaking technical nonsense. The coolant manufacturers used to specify coolant was good for two years or 60k miles. I noticed that no one ever seemed to ask why it was specified this way. As I can tell the limiting factor for the coolant life is time spent at temperatures in excess of 50C.Try controlling that under warranty! Even my Prestone green coolant now says it is good for 5 years or 130k miles. I recently checked the pH of my coolant after 4 years and it was 8.5- still plenty of life left in it but I changed it anyway. This explains why some examples can sit for many years not being used and nothing happens to them.

Sadly to date I have not been able to think up a way of testing to determine whether the heads are under attack and if so what triggered it. Unless and until we can achieve such I suspect it is prudent to plan on pulling the cylinder heads every 15 to 20 years and be prepared to deal with corrosion damage should it happen.

worf928

First, let us separate the two 'head' issues: head gasket life and head corrosion.

Ok. So, how long do they - head gaskets - last? Under the most ideal circumstances. How long do they last? Your '85's head gaskets are now 35 years old. We agree that they don't last forever. How long do they last?

We've seen many, many pictures of head gaskets. Some of them are developing the 'holes' that isolate #4 and #8 cylinders.

Do we think that those pictures are statistical outliers? Or do we think that they are a significant sampling and therefore representative of the condition of the gaskets of the fleet? (Pedantically: in the set of pictures we've seen some are pretty ok, some are super bad, but most show signs of significant deterioration.)

Do you think Porsche - in the early 70s - designed them to last for 100 years? 50 years? 40 years? 20 years?

So, when I say "I think it's a good idea to plan for head gasket replacement when they are in 30 to 40-year old range" you think I'm being hysterical?

Ok. So, how long do they last?

This is the "corrosion problem." Again, let's ask if the condition of the heads that have been pulled are anomalies or representative. Let's not even discuss causes or history of coolant changes. Let's just ask "are these heads representative of the fleet?"

Both problems are 'creeping' problems. Head gaskets get steadily worse and corrosion gets steadily deeper. The nice thing about head gaskets is that they have a fixed cost. Correcting corrosion on heads is NOT a fixed cost. The longer corrosion is allowed to eat away the heads the more expensive the heads are to fix.

Either problem can kill a 928 engine. If not "kill" then make it so expensive to fix that most 'mortals' will throw in the towel.

So, ask the questions:
- how long will my head gaskets last?
- how long do I want to allow corrosion to eat my heads?

Right now we are looking at 928s with 26 to 43-year old head gaskets. Within the next decade that will be 36 to 53-year old head gaskets.

Am I really spreading hysteria when I suggest that it is a very good idea to pull heads in the coming decade if it hasn't been done already?

Am I really spreading hysteria when I suggest that head gaskets failures or corrosion will claim a lot of 928s engines in the next decade when they are 36 to 53-years old?

Ok. So...

How long do head gaskets last?

HOW LONG DO HEAD GASKETS LAST?

I think a lot of people don't really think about the age of our fleet. They just look around when driving and they don't see head gaskets popping left and right and they don't hear about the neighbor needing to replace head gaskets on the Honda minivan that will be on the output side of the crusher when it's 25 years old.

What's the percentage of cars on the road that are over 30 years old? Google it. See if you get different numbers than I did...

Numbers I found are: less than 1%.

We're not considering "typical" problems that cars have. We are looking at problems that happen in extreme old age.

worf928

Did you ever read the SAE papers I pointed you at in the other thread?

In any case, you don't need to convince me of crevice corrosion.

However, I think you are underestimating the problem.

Our heads are cast in a mold without pressure. Such castings are porous. Only the 'outside' layer is 'solid.' The inside is a sponge. It is porous. Once corrosion eats through the 'solid' outside it can very easily tunnel through the 'sponge' and thus deck corrosion is only the tip of the iceberg. The more porous is the casting the quicker coolant corrosion can 'eat' through the casting from top to bottom.

The more porous is the casting the more difficult and time consuming (and therefore expensive) it is to weld material into the head to repair the deck surface.

The porosity of the 928 heads seems to increase with model year. ('87/'88 heads seem pretty 'solid', '90/'91 not so much.)

This is why I am more concerned with the 'youngest' heads. They seem to be the most porous and therefore the most expensive to fix when corrosion gets into the 'sponge'.

And it is crevice corrosion that accelerates the sponge eating.

worf928

Is that where we are headed? We stick our heads in the sand and rather than suck up the expense of doing heads now we wait until all the heads are dead and then we have to make new ones?

Well... ok.

Got nothin' to say about heads other than 928 heads.

But didn't we cover electrolysis in the 'big' thread?

What's different about 16v, 32v S3, and 32v S4 motors that would drastically change the 'lectrical characteristics?

I'm going with casting porosity.

In one of the other threads I related a story from a Porsche head tech. I'll do it again here:

A half-decade ago the porosity of Porsche castings got to the point where some of the 997/987 motors would leak oil through threaded bolt holes. The casting was so porous that drilling and taping holes in the block for accessories (etc.) opened up 'the sponge' to the extent that oil would simply be 'forced through the sponge' and out the threaded holes.

linderpat

Really Dave, SHOUTING at me? Screw that. I don't give an eff how long they last. I know GD well that they don't last forever, like ANY car. It's a maintenance item. The corrosion is what I am talking about; that's where the stink is being made. But like I said, you miss the whole point. You think there is some virtue in every single 928 auction to provide a PSA as to how these engines are rotting under our noses, and helping to drive the myth that 928's really do suck. Leave it here in the technical forums where it belongs. If anybody is sourcing an aged supercar and not doing their homework, then shame on them.

Anyway, I'm done here. I cannot compete with the smartest guys in the room. Sorry I ruffled your feathers!

uraniummetallurgist

Crevice corrosion requires chloride in the solution to break the tight and protective aluminum oxide surface protecting the alloy below. Crevice corrosion is a normal situation on offshore rigs where it is a major problem. Much less so in the relatively chloride-free environment (recall the antifreeze instructions to use distilled chloride-free water) inside the cooling channels of the motor. As I mentioned in a previous post, galvanic corrosion is a much more likely cause due to the failure of the head gasket allowing iron based alloy to contact aluminum resulting in a current caused by dissimilar metals in contact.

In addition to changing the coolant, head gasket should be inspected and changed as required.


All the best,


Joe

worf928

Hmmm... I see. So it's not really about head gaskets or deck corrosion. You are pi$$ed at me for comments on BaT about crank-end play measurements.

Got it.

GregBBRD

No, he's pissed at me about my comments on BAT about potential head gasket and corrosion problems on a low mileage '88 and my comments about the GTS in this thread.

Since he wasn't/isn't the seller or the buyer of either vehicle, but just another observer, I'm completely at a loss to figure out how this affects him.

What I really don't understand is the motivation behind trying to hide reality from potential buyers....

4664

So, what coolant should actually be used in the 928?
Surely that would make a difference too?

• Inorganic Additive Technology (IAT)
• Organic Additive Technology (OAT)
• Hybrid Organic Acid Technology (HOAT)
• Hybrid Organic Acid Technology (Si-OAT)

DexCool is OAT, but more recent Porsche engines require Si-OAT.

FredR

Despite what many seem to think it would make absolutely no difference whatsoever- they are all ethylene glycol/water mixes and will all suffer the same fate cylinder head wise were they to be used in a 928. .

That being said our engines were designed for use with the one and only coolant type available up until 1994 and that is IAT coolant. In the States you recognise this as "green coolant" and in Europe it was commonly marketed as either green or blue coolant. The blue version came from Germany- more specifically BASF who own the Glysantin division. The German version [as best I can tell] was referred to as G10 coolant the G10 being a VW designation.

As best I could fathom in my research this type of coolant became a universal standard coolant after world war 2. The derivation root came from British aero engines- specifically the one and only Merlin engine. This was an all alloy water cooled engine. At the start of WW2 as best I know US aero engines were invariably those horrible radial air cooled engines made by the likes of Pratt and Whitney. The Luftwaffe engines made by the likes of BMW were all water cooled engines- it gets pretty cold up there in winter time so they needed a coolant that would not freeze at minus 30C- nothing could compete with ethylene glycol and water thus it became a universal coolant after WW2. The colour is irrelevant. The US auto industry liked dayglo green because it was easy to see if rust from the cast iron components was discolouring it and if so they then knew it was time to change it. The Germans went for blue for whatever reason. The notion that IAT coolants are not suitable for use in alloy engines is therefore laughable. As I can tell they remain the best coolant available and now my IAT green coolant made by Prestone is rated for 5 years or 130k miles. They say they improved the chemistry but I have a feeling it is the same stuff they used to sell as only being good for two years. I have never seen IAT coolant lose its pH value in two years or even 4 years for that matter.

In the 80's politics started to dig in and there was concern about the amount of this stuff being discarded and environmental pressures started to demand longer life coolants. Thus the first generation OAT coolants emerged- trouble is the first gen versions were awful and for want of a better phrase were initially abandoned by major marques. The first real world solution emerged in 1994 when Glysantin introduced their G-05 coolant and offered it as a replacement for IAT coolant and offered it as being good for 5 years or 130k miles and it was rapidly accepted. The trouble was that the German manufacturers never recognised it.US companies made it under license from Glysantin and thus the likes of Valvoline G-05 came to market. Eventually VW saw the light and in 1998 adopted their G11 spec. As I can tell this was adopted by Porsche and MB and the colour was blue as it was intended to be a replacement for their G10- they are supposedly backwards compatible and this is the current spec of choice for our 928's. Purchase it as a generic coolant and what costs you US$10 will cost you $20 in a VW bottle and US$30 in a Porsche bottle!

G11 is a HOAT chemistry formulation, G05 is also a HOAT chemistry formulation and the notion that G11 will work for a 928 and G-05 will not is complete nonsense. The only difference is that G-05 contains a nitrate component that is designed to protect against a specific type of corrosion known to wet liner engines- no need for such in a 928. Many 928 owners have used G-05 with absolutely no problems.

As engine designs and materials used in them changed the G12 coolant emerged- this is pink in colour and is used in vehicles like Cayenne 955 Turbo S. As I understand it is not suitable for use in our 928's and G11 is not suitable for use where G12 is required. The latte is something to do with more modern engines having smaller passage ways in their more efficient coolers that will block up if older type coolants are used.

The names G11 and G12 are proprietary names of VAG coolants. As I can tell non of the German companies design coolants and Glysantin are the brains behind such. Ever wonder why VAG used the pre-fix G in their coolant specs? Glysantin on the other hand make the same coolants in their own house brand name. VW G11 is Glysantin G48. VW G12 is Glysantin G40. Confused? Grab this- VW later modified their G12 to G12+ and G12++ and then said they can be used instead of G11. Then recently they introduced another coolant spec that covers anything and everything [supposedly].

As for Dexcool, well if you are into Gello throw a jar of that into your cooling system and see what happens to it!

namasgt

Greg,

Are you seeing equal number of 87 & 88s with the head cracking issue around the head bolt holes or do you see more 87s with this problem?

drooman

Dave, I don't see how having a discussion about remanufacturing heads is about sticking one's head in the sand, not saving the heads that can be saved, or waiting until head supply is at zero before considering remanufacturing.

If we take all of the heads that were made from 87-95, it seems like a very low percentage of them would be in good shape:
- Cars that had whatever history formula made them survive well (miles, coolant changes, use pattern, etc) whatever this formula is seems hard to nail down definitively.
- Engines that have been rebuilt in recent years with required head repairs and subsequent care.

That's it, and according to many multiple representations over the years by the people who are regularly opening these engines up, it is a low percentage of engines.

The general consensus seems to be that the rest (ie; significant majority) of the heads currently out there are in the process of rotting, completely rotted beyond repair, or in the case of the 87-88 were defective in other ways. Since the cars are becoming more valuable, and the "supply" of good or repairable heads is not increasing, not staying the same, but absolutely decreasing with time, then yes..remanufacturing is where we are heading. As with the Ferrari 250 heads and the countless american V8 head offerings, *new* 928 heads could be BETTER than the Porsche units EVER were. I know that the 250 ferrari heads are superior to the finest originals and cost around $30,000 per set... but remember they are V12 heads and fit on a Ferrari. What happened on those heads is that the supply of repairable ones got very low, then the heroic measures to save them got more expensive, then new heads came out and most engine builders are NOT saving old heads because they will NEVER be good as new heads, then this justifies paying more for new heads instead of repairing old ones. This is an important concept of considering remanufacturing, they have to be BETTER than the originals ever were.

I'd like to hear from someone with more knowledge in this type of product development about the costs involved. What can you professional 928 engine builders sell a set of new heads for? What might the development costs be? The formula works for chevys with cheap parts and many clients, and it works for Ferraris with few clients and high prices. What do the numbers look like for us?

4664

Thanks for the DETAILED explanation. Much appreciated!
I had previously perused these sites:
https://blog.fcpeuro.com/how-to-pick...t-for-your-car
and
https://www.valvoline.com/our-produc...engine-coolant

From what I gather, VW G11 is closest [or identical] to: Valvoline ZEREX G-48 (HOAT (Hybrid OAT, Phosphate-free, turquoise in color))?