GregBBRD

Truthfully, I've seen one engine in the past 5 years that didn't have head gaskets in a complete failure mode. And I suspect that the gaskets in that engine had been replaced, at some point in time.

The head gaskets, in our 928 engines are beyond the end of their life. (Low mileage engines suffer worse than high mileage engines.) That "paper" is done. The ones that are not leaking into cylinders have holes in them, interrupting correct coolant flow through the cylinders and the heads, damaging the rear pistons and cylinders, from excessive heat.

If anyone has an engine that has not been apart, a coolant change is not going to "fix" the damage. At this point, the "target", for me, is to keep the rest of the aluminum pieces from disintegrating.

I should take some pictures of thermostat housings, thermostat covers, head gaskets, etc. It's a horror story.


There's a ton of threads, on Rennlist, about which oil to use.

Forget the oil....it's not the long term problem. Poor in anything that is 15-50 or 20-50 with 1100 ppm ZDDP.

Damage from acidic coolant is the real culprit!

polecat702

Greg, Are you saying that we need to pull the heads when doing a intake refresh? I'll be doing mine soon, I have my spare intake and valve covers back from blasting and painted by our own Don Buswell, and they look fantastic!

Do I bring the heads to you for rebuilding? I don't trust anyone else.

GregBBRD

It is definitely time, if you suspect they are original. Regardless of whatever they "soak" or apply to head gaskets....in the end, they are just paper. 35-40 years of paper soaking in acidic water....it's time.

I'll post a couple of pictures of the head gaskets out of this 100,000 mile GTS.....which are not as bad as most I see (the fire rings look perfect, but the acidic coolant ate away the head between the gasket and the head), but the engine still had a catastrophic "water" related issue.

It wouldn't be such a problem, if Porsche had inventory on replacement pieces. No oversize pistons for '85/'86. Six oversize pistons for GTS. No GTS crankcases. No "sets" of GTS camshafts. No "sets" of GT camshafts.

This makes fixing some engines a real challenge.

Judging where the prices are at/going on 928 vehicles....can anyone "afford" to not pull the heads and address the issue, before it is catastrophic?

I used to do heads, in house...because I could not find anyone that I really trusted to do what was needed. I've now got someone I trust to do the work to my standards. I still have to tell them, each time, exactly what I want done (they do heads for other people who have completely different standards and expectations.) I can certainly "manage" people's head rebuilding....just keep in mind that my trusted machinist is busier than I am....and with as much work as I take to him, I have to wait in line, too. (People that know how to do engine stuff correctly are getting few and far between....and are generally very busy.)

polecat702

Thanks for the honest, and informative reply Greg!

jetson8859

Here are before and after pics of the heads from my 93 GTS. I do know they had new gaskets in October 2006 as I have receipt from Reeves Porsche in Tampa detailing work. The car had green coolant when I bought it in Feb 2016 and I flushed it and filled with G-05.

We took 1.5 thousands off as part of project and they turned out pretty nice. Will also get Colin's tri-flow cams, new valve stem seals (guides were good) along with PAC Racing springs and retainers, Ferrera seat locators, new rings, 48lb injectors and a sharktune.

928 GT R

Here is an alternative and admittedly AR method that I have used for nearly two decades.

Start process with an engine that has gone for a spirited run and has cooled enough to work on.

1. Drain radiator and block drains, then refill with distilled water.
2. Heat cycle engine with heater on and blasting heat into the cabin.
3. Drain radiator and block drains and remove and fully empty radiator.
4. Pressure rinse out external insect debris from the radiator core using a hose from the engine side, then inspect and remove tiny stones with a blunt dental pick. Straighten dinged radiator gills as necessary.
5. Pour a half gallon of distilled water into radiator while it is lying flat, lift radiator (keeping it flat) and roll it in a circular motion to agitate water in radiator. Drain through a fine screen to inspect for contaminants (repeat as necessary until there is no particulate in radiator.

6. Refill with 60/40 mixture of G-05 and distilled water to result in a closer to 50/50 mix because the heater core and a few other spots will have mostly distilled water in them.

Note 1: It is silly easy to remove the radiator from a 928 when performing a coolant change. Just do it and keep this vital system clean of external and internal contaminants!

Note 2: I may be switching to Greg's suggested factory coolant (000 043 305 75) in the future.

Note 3. I have been performing these changes on a bi-annual basis, this is overkill and am adopting a three year coolant flush cycle.

Note 4. Never introduce any tap water into your cooling system unless performing a terminal cleaning of a newly purchased vehicle that has a poorly maintained system with crud in it.

Note 5: All this effort only extends the life of the cooling system and reduces damage of inevitably failing head gaskets.

NoVector

And this is why I have trust issues:

FredR

I have a deep suspicion that the problem these cars face corrosion wise is a mix of the coolant being left in the car longer than it should and examples that sit for too long without running. When the coolant sits stagnant for too long I suspect that the time based degradation of the coolant is worse at the high point, acid conditions form and the by then acidic coolant then nibbles away at the gasket, the top of the cylinders and the cylinder head face where the gasket used to be. The phenomena is known as crevice corrosion and is prevalent in aqueous solutions that can form acidic conditions. Running the motor up to temperature briefly on a regular basis may well help stop such degradation simply by circulating the coolant. If the car is going to be left static for long periods of time it may be better to drain the coolant completely.

The original GTS motor that was fitted to my current 928 had head corrosion problems and I know for a fact that the poor thing sat for weeks, maybe months at a time without being operated and that before the TBF hit the motor. My S4 motor never sat stagnating for very long- perhaps a month at most during a leave period. When I lost my 90 S4 it was 15 years old, had covered about 130k km and the cylinder and heads were perfect as was the head gasket we removed suggesting it had more life left in it. If the car is used regularly and the coolant changed at appropriate intervals I think it is a fair bet that the head gaskets will last 20 plus years. The current gaskets have been in situ for some 14 years and my long term planning is thinking along the lines of pulling the heads once the gaskets have been in-situ for 20 years. If list experience suggests they will last a bit longer than that all well and good.

Whether this theory holds remains to be seen but it is interesting that GB suggests that higher mileage vehicles present less problems and that fits the above theory well.

SeanR

Low mile '91 I did about 6 years ago.



High mile GTS that was well maintained I did 6 years ago.



115k '88 from last year.

dr bob

^^^ My highlighting/emphasis above ^^^

I'm against this idea, as experience has shown that the paper gaskets dry out, and exposure to oxygen after acidic coolant exposure does more damage in storage. A couple wet-sleeved (steel sleeve in aluminum block) engines suffered severely following dry storage for about ten years after less than five years in service. I've resorted to 'pickling' stored engines in kerosene, in hopes that the corrosion devils will drown. I'll find out some day if this is effective at protecting head gaskets; I can easily replace those, where restoring corrosion-damaged metal parts is a bigger challenge sometimes.

If a stored engine has been thoroughly flushed with distilled water prior to storage, maybe with detergent and some buffering as part of that process, then vacuumed and storage dessicated in a sealed bag, you might be happy with metal survival in long-term storage. The paper gaskets still dry out, and seem to fail within a few months of return-to-service. In my limited experience with such things anyway.

A fellow enthusiast proposes a long-term coolant system pickling with distilled water, Water Wetter, and a healthy dose of soluble oil if the whole cooling system is intact. (engine, radiator, heater, hoses etc, still in the car). I might add sacrificial zinks to his method, with regular inspection.

polecat702

Is it best to pull the engine to get the heads off?

FWIW the Zerex web site says the G-05, is good for 5 years/150,000 miles in light duty applications and 3 years/300,000 miles in heavy duty applications. I change mine about every 3 years wether the car is driven much or not. I haven't put 5,000 miles on my car in the last 3 years. The oil still looks golden.

I have a spare engine, so I think I'll pull the heads off of the spare, have them rebuilt, and do the swap, when all the parts are here and ready to go.

dr bob

I wonder what differences the coolant experiences in "normal" or "light duty" applications vs. "heavy duty". Except perhaps for bigger temperature variations within a system, I'm not seeing how the flowing liquid in the passages knows whether the engine is working hard or hardly working. I'm with Joe on following the "severe service" schedule on almost everything. I spend time waiting at the drive-through, poking along in traffic, moseying casually through the nearby mountains and deserts, dashing to the store when the mood hits me. None is tough duty, but it's also not gentle steady low-load cruising. If it's not 1500 RPM cruising with under 50 lbs/ft torque load in 60 degree ambient air, it's "heavy duty" at least as far as maintenance scheduling goes. Two to three year intervals works out well for me, including a change at the six-year timing belt replacement party.

If I had that spare engine sitting around, it would get the full cleaning, inspection and reseal including all gaskets. Heads would go to Greg and his machine shop que. Then the whole thing into a plastic bag and at minimum fogged, vacuumed and dessicated for storage.

FredR

Bob,

In this instance it seems we have a somewhat different take on the issues associated with the cooling system.

The notional first discussion point is the perception that process fluid wetting of the gasket is an inevitability. As I am concerned if the process fluid migrates into the body of the head gasket the thing has failed. I do not know any details of the head gasket construction but every flexible gasket I have worked with has a fibrous body of some kind and a binder that holds it together. If the binder fails the gasket fails. When I removed the head gasket from my S4 motor it came out in one piece in seemingly perfect condition with very little in the way of fibrous material deposition on the head and crankcase faces. If the gasket were made purely of paper that had been wetted by the coolant I suspect that the gasket could not have been removed in such condition. Mix paper with water and it will invariably form a mush.

The second point is that whereas we are constantly told that acidic coolant conditions are to be avoided [and I believe they are], have you ever seen a corrosion problem reported where an across the board weight loss corrosion event has occurred [i.e. corrosion on all wetted surfaces]? The common failure is invariably at the head joint and it involves the top of the cylinder or the face of the head [or both]. If the gaskets hold up on some cars and not on others it cannot be a random coincidence rather there has to be a reason for this. The only logical reason I can think of that might cause this to happen is if something causes the gasket to break up. I suspect that "something" is most likely an acidic coolant mix that eats away at either the binder or perhaps the fibrous content whatever it may be. I know that concentrated hydrochloric acid can eat paper but i doubt there is anything that potent present. Once the gasket has been damaged by process fluid wetting joint failure is inevitable.

Finally, gaskets only work if they retain their elasticity. They are designed to operate within specific stress ranges thus why they can heat cycle many times, over many years and retain their seal. If the cooling jacket is drained the gasket should retain its seal. If the gasket material is process wetted then indeed I would think it could well dry out and subsequently fail but the problem is the wetting of the gasket material in the first place. If such were a routine event then I would expect the WSM to advise that if the block is drained down the head gasket has to be changed- I have not seen such caution to date.

I thus concluded that for the head or the cylinder top to corrode something else has to be going on. My perception is that if the gasket material gets wetted, it does so because the binder has failed, the coolant finds its way to the metal surfaces and then the crevice corrosion phenomena kicks in wherein ionic fluids trapped in a crevice causes a dramatic and very localised increase in acidity and that is what eats the metal surfaces. Keep the coolant alkali, cycle the coolant regularly and the gasket survives. Expose the gasket to stagnant acidic coolant, the gasket fails and metal gets eaten. Low mileage engines can and do stay static for long periods of time, high milers are invariably used all the time thus less vulnerable?

This is my theory as to what happens within the cooling jacket of these engines that ultimately leads to severe engine failure and I have yet to see a better explanation should such exist. If there is hard evidence that something else is going on then all well and good and I for one would like to know what it is.

When it comes to flushing the coolant chamber with water, I have no problem with using high quality water but similarly I have no quarms about using a hose pipe and tap water to flush the system. I would prefer not to use hard water and if I had no choice I would subsequently fill the system with distilled water, drain it and blow the system out with compressed air to dry it.

dr bob

Hi Fred --

My casual experience is with a few British engines that started out life as Ford or Ford-design blocks. Aluminum twin-cam heads on iron blocks, and aluminum with steel wet sleeves and aluminum heads. The head-gaskets failed during storage. Whether they rotted due to wrong gaskets, wrong coolant, whatever, I can't say. They were stored without coolant after "normal" service, whatever that is for engines in weekend race duty. For that duty, "coolant" is limited to water plus a very short list of optional surfactant additives like Water Wetter. Just sharing the experience.

From that and the other observed deterioration, I upgraded the storage prep protocol for the remaining bunch and some new additions. At this point I plan to tear down, inspect and reseal each of the stored hoard engines before placing them back in service.

For those playing along at home, I'm a recovering early Lotus addict. I'm not ashamed of it anymore. It's part of my auto history, nestled among Porsche and F-car (and others...) addiction periods. The 928 has by far the greatest performance/$ ratio of all but one or two in that history. At some point soon the remaining hoarded cars and spares collection will be offloaded to someone who is currently addicted. The last one I sold (for 928 garage space) lasted less than six months before the new owner backed it into a guardrail. I need to be more particular about who buys them I guess.

FredR

LOTUS- Lots Of Trouble Usually Serious!
Great when they are working which is not too often.

I have a 1996 Daimler Century 6 litre Vee 12 engine- one of 100 made, not sure how many were left hookers or how many of them are left. They also made 100 with the 4 litre straight 6 motor. It was a superb car and very reliable until it was about 16 years old but then some 7 years ago everything started failing at once- makes the 928 look like a paradigm of reliability and sensible motoring. It is going to take about $6k to restore. The heart wants to do it common sense says I should walk away from it.

We must be infected with the same virus!