ador117

Bonjour,
Last track day was great. High temperature but no warning light.
However coolant was blown over the reservoir cap. First I thought that the cap was wrong. I bought a new one and when replacing it, engine cold... PSHIIIIIT... the cooling system looks pressurized..
Damn...
So I bought a Rapid Engine Leak Detector... and the verdict is on the video attached...

One head gasket is toasted... I verified with a bore-scope but I see nothing wrong...
I re checked my compressions this time with a FACOM tester and I found 12 bars on 5 cylinders... slightly less than 180 PSI... so it is time to rebuild the engine...
I'm so sad... hard to realize that I will stay month without driving the car... at a moment she was working better than ever...

To make sure my leak detector is not wrong I checked on another car and the liquid remain blue...
I will pull the engine out and report what I will found. Comments and advises will be welcome.
Have a great day,
Raphaël

ador117

here is the video :

karl ruiter

All 928s that have never had them will be needing head gaskets about now, so not a surprise and nothing you did wrong.

SwayBar

He had previously tuned the engine, and it may have been too aggressive, detonated, and blew the head gasket.

Speedtoys

Detonation blowing it out..
Cant say until we see it.

FredR

Raphael,

Whereas there is little doubt that you have a head gasket issue I trust you understand that the 5 cylinders exhibiting 180 psig compression test pressure are perfect. What readings did you get for the remaining three cylinders?

There are two possible reasons why the head gasket has blown- one is a pure head gasket failure for whatever reason, the other is if corrosion has set in- that can ultimately get to and damage the fire ring in more extreme cases. Either way if the gaskets are the OEM build then chances are the gaskets are shot due to the inherent problems that manifest themselves with age due to what I consider to be a design flaw. Had Porsche issued a technical bulletin advising owners to change out the head gaskets every 20 years then my perception would probably be different- not that it makes any difference,

The heads on my current motor were pulled at 15 years back in 2005 and they were in perfect condition. I have seen three sets of heads over here that failed when about 12 years old and the heads were written off by Porsche due to the corrosion damage- Porsche does not recognise or support welding up of corroded heads and thus does not sanction such- a bit short sighted given the attrition now being taken by cylinder heads 30 pus years down the line as it were but that is their problem.

ador117

Bonjour,
The intent of my tuning was to keep the level of performance I had with my previous performance chips and make sure correct amount of fuel (more) is injected in order to lower the temperature inside the head, using E85 fuel. I stay at least 2 or 3 degrees of advance before detonation...
I would be surprised if detonation is the cause of the failure. But reality is reality and we will see when engine will be out and open.
I have no idea on how the coolant was managed before 2011... and since, I changed the coolant on a regular basis. However I used approved G-48 coolant only since this winter... before that I used high quality Porsche approved coolant but not sure they where good for the 928..

Compressions measured after the track day were (12,4bars = 180PSI).

Compressions are between 12 and 13 bars, looks good to me first. But after reading some post here, my understanding become that below 180PSI, engine rebuilt is recommended.
I understand it wrong?
Have a great day,
Raphaël

FredR

Your compression pressures are perfect as I am concerned. The perception that cranking test pressures of less than 180 psig indicates an engine rebuild is technical nonsense.

The test rig checking for exhaust gases appears to be a problem of legitimate concern

JET951

Do you really consider head gaskets that last 20 and in most cases 30 years a design flaw? they are gasket and a perishable item, particularly combined with owners that don't perform consistent coolant changes. Then we need to take into account a 928's unknown history, in its past life did it pop a radiator hose at some point causing an overheating event? or did the fan control system fail at some point causing a similar event? these all subtract life from the ever lasting gaskets.
Regards
Sean

GregBBRD

Raphael:

I'd personally quit running or even turning this engine over, with the starter motor.
A blown head gasket is one thing.
A split cylinder from hydraulic forces is another.

Take it out and take it apart, before it gets any uglier....

ador117

Bonjour,
yes… no intention to run this engine anymore. Too much risk to fill a cylinder. I don’t understand why I see no water inside the cylinders…
Last time I run the engine was for the video. No smoke at all…
reality always oblige to revise what we think…
have a great day…

FredR

Raphael,

When you pull the motor and remove the heads in all probability I suspect you wll find corrosion has taken place of the kind I have defined elsewhere and on one of cylinders you will probably find this has undermined the fire ring leading to a tiny pinhole type leak path. The combustion gases at much higher pressure find their way into the cooling system and that would have caused the cap on the expansion tank to lift at 15 psig. The cooling system at 15 psig cannot blow back into the combustion chamber through the pinhole and so you do not see any coolant in the combustion chamber as things stand.

GregBBRD

I'm not sure that the people who I've installed sleeves for cracked cylinders in their GTS engines or the ones with connecting rods broken off and sticking out the side of their engine would completely agree with you.

Yes, the combustion pressure far exceeds the water pressure, so when the engine is running...no problem (except for the over pressure and water being ejected from the overflow tank.)
Once the engine is not running is when the "disaster" can strike.
The coolant backflows through the tiny hole and fills the cylinder with coolant.
The "next" cranking event can turn an engine quickly into scrap metal.

If someone is "feeling lucky", it's no sweat.
However, I don't crank these engines over with the starter.
My momma raised no fool.

FredR

The OP asked a simple question and I gave him a technically logical response- he did not ask if it was OK to continue running his engine, he did not ask if it was OK to crank the motor and he has advised that he is going to pull the motor and investigate/rectify whatever the problem may be- is there any point in there that you did not understand?

FredR

Sean,

I suspect your point of view is based on significant experience that you have come to take for granted and thus is your "norm". My point of view is seemingly quite different- with over 40 years experience managing engineering in the oil industry I look for "what should be the case" rather than "what is the case" which probably better defines your understandable but as I am concerned incorrect perceptions.

I have owned 928's for the last 23 years - two of them to be precise- a 90S4 that sadly I lost in a big accident caused by some tw*t on a mobile phone and then for the last 16 years a 92GTS powered by the engine from my late S4. When we opened my S4 motor in 2006 to my relief the heads were in perfect condition, i have no meaningful recollection of the state of the gaskets but there was no mention of anything untoward. If every engine emerged from say 20 years of service like that I would say that would be a "perfect design". Unfortunately that is just not the case and I am sure you well know that and doubtless you will have seen many examples of corroded heads.

Nowadays we see S4/GTS motors being pulled with 30 years of service on factory gaskets, some pulled because the head gaskets failed and some pulled because the owners have elected to have their motors opened. What I have noted in these motors is that invariably they show varying degrees of head corrosion and this has created the false paradigm that somehow this is "acceptable". The head gaskets also show signs of damage varying from mild to catastrophic but such damage is not "aging" as you perceive rather it is due to a chemical attack. Just as with other practioners you instinctively blame the coolant but have you ever tested the pH of the coolant in the engines you sare pulling? If the coolant was responsible for the degradation then the block side of the exposed gasket surface that is continually exposed to flowing coolant would be attacked on each and every 928 engine and that just does not happen- once this fact is considered it destroys the perception that gaskets "age by exposure" and is totally consistent with the perception that the gasket attrition is caused by an [acid] attack coming from the head side of the gasket.

During the initial years of operation the gasket generally stops coolant from getting between the gasket and the heads in those areas bounded by the cylinders and those cast-in ports and while that status quo holds there is no problem. Those ports are open at the back of the coolant bath and thus permit coolant to flow into the heads and back to the radiator to complete the circuit. At some locations the gaskets actually have small holes in them to permit controlled amounts of coolant to flow into the heads thus providing additional/balanced cooling at the top of the cylinders. The problem is that with passage of time the status quo is interupted and coolant gets into the very small gap [the "crevice"] between the gasket and the head. When this happens the anti corrosion package gets depleted rapidly and then it is "game on". The big problem with ethylene glycol is that it thermally decomposes at temperatures above 55C. When the chemical package is in play this is prevented by buffering the glycol such that its pH is alkaline and lies within the range pH9 down to pH7. At some point around pH6 the glycol breaks down when heated and an obnoxious mix of organic acids is formed. These acids slowly but surely nibble away at the both the heads and the binder material of the gasket and at some point the passive protection film of aluminium oxide breaks down and the alloy is then vulnerable to corrosive attacks. Once this starts it is just a question of time as to how long the system can function without issue which seemingly can be quite a long time.

At the other end of the scale three years ago we saw an example of a perfectly re-built engine that was opened up after three years/30k miles of service and this problem, although not at serious levels of degradation, nontheless had its teeth into both the heads and the gaskets. At the time the coolant deployed somewhat understandably was blamed simply because those involved had nothing else to blame it on - not surprisingly those involved [on their own admission] admitted they knew little about corrosion and coolant chemistry and there was no reson why they should - however yours truly does know quite a lot about such matters and the evidence was such that there was no doubt that the coolant deployed was "guilty by association" and nothing else- there was not a scrap of engineering based evidence to support the notion that the coolant was responsible. On the other hand I knew precisely why the corrosion had set in and even I was astounded by the fact that it happened so quickly despite a most perfect build. This confirmed my suspicion that onset is a random affair influenced by something whatever it may be. Interestingly the coolant deployed [G-05] has identical protective chemistry to that of the long life coolant Porsche recomend for our engiens, put in a bottle labelled as "Porsche coolant" and charge the earth for. The G-05 coolant was developed by BASF in Germany under their Glysantin brand and was deployed in 1994 as a universal cooant to replace the original IAT bsaed version. Four years later in 1998 BASF deployed a similar coolant without an element that is not needed in our motors and called it G48. VW Audi put this coolant in their own brand bottle and called it VW G11 and were duly followed by Porsche deploying the same coolant in 1998. From what I can ascertain what you purchase for US$10 in a bottle labelled G48 you pay double that when it is in a bottle labelled VW G11 and triple that when it is a bottle labelled Porsche and they are one and the same thing manufactured by BASF.

Needless to say our motors were not designed with these coolants in mind - they were designed to use IAT coolant which until 1994 was the only grade of ethylene glycol based coolant that was available globally. In Germany and many parts of the world it was coloured blue. That is why the G48, VW G11 and Porsche coolant currently recommended for our engines have a blue dye added because they are considered compatible with the original IAT coolants and thus can be mixed not that that is likely to happen these days. In the States the IAT coolant is green and known as Prestone. The original IAT formulation had nothing technically wrong with it and the ony issue I know of was it has to be diluted using distilled water quality- mix it with hard water and your cooling system will be covered with scaly deposits. This coolant has a "limited": lifespan that was hard sold as being 30k miles or two years but this was a misrepresentation as glycol based coolant lifespan is controlled by run hours at temperatures in excess of about 55C.

Political pressure from environmentalists led to a drive to achieve coolant lifespans of 5 years or 130k miles. My motor has only ever seen IAT coolants and for most of its 32 year life has run using Prestone and is now 17 years into its second iteration. The irony is the current version of Prestone is now rated as being good for 5 years or 130k miles. Now you may well ask why do i raise this point? Given my motor had no head corrosion issues 15 years ago and has now run for 17 years without any issue, this left me wondering whether there was something in the so called "long life" coolants that for whatever reason induces the gasket to let coolant into the crevice and initiate problems- a long shot- I doubt that happens but....?

Finally, I consider the 928 head joint very robust whilst it is working as Porsche intended and it can obviously take way more attrition than a stock motor can throw at it. The head gasket failures I recall were invariably induced by corrosion weakening the fire ring seal. I dare say genuine failures have occurred and if such happened then I expect it would be somewhat obvious as the head would likely be distorted by such.

Hopefully the above may help you understand that there is much more to this issue than initally meets the eye. Interestingly I have looked into over 50 cases of head corrosion, most on this list, some on other organs and some 18 years ago on 3 examples in the flesh as it were. I also have a pair of moderately corroded heads gathering dust in my garage. Each and every example i have studied exhibited exactly the same chartacteristics. The most startling piece of info I deduced was that not one of these cases showed any evidence that the problem was caused by spent coolant. If in your record files you have any photographic evidence that compels you to believe that such happened on any 928 [or 944/968] you worked on- kindly post the photo and I will be happy to advise whether I concur with your assessment for whatever little that may be worth. I would truly like to see/examine an example that was caused by such but I have a feeling that Unicorn is just not going to happen.

Kindest regards to you and Bruce.

FredR