HG replacement prep
07-19-2022, 05:21 PM
#16
Rennlist Member
I find it interesting that on my Cayenne Turbo S that motor has a closed deck construction and on the likes of the 996 and 997 variants the gaskets are now completely sandwiched even with open deck constructions so presumably Porsche have learned where they went wrong on the 928, 944 and 968 platforms that all appear to have this issue. It is a fair bet that other marques have similar issues given most if not all use glycol in their cooling systems but I have no known data points about such.
Hopefully, my definition of a sandwich is the same as yours. :-)
07-19-2022, 06:14 PM
#17
Rennlist Member
My definition of "sandwiched" in the context of my comment is that the gaskets are now trapped between solid surfaces on both the head and the block sides and therefore the coolant cannot be entrained between the head and the gasket to cause the subsequent long term mayhem the 928 configuration experiences- doubtless they eventually fathomed it out as they saw example after example rot. I saw several sets of heads rot over here some 16 years ago that were cast off as scrap by the main agents as Porsche seemingly would not endorse such repairs. It never ceases to amaze me as to how folks blame coolant change intervals for this problem and then you see the transfer passages in the heads in immaculate condition not to mention the rest of the water jacket and the radiator show no signs of corrosion- how folks could think the problem was caused by the condition of the coolant or the coolant type/make is beyond me. Make no mistake coolants get exhausted as and when the pH drops below 7 and if and when that happens signiicant damage can be expected to commence at around pH6 but that would happen on all coolant wetted surfaces. I have never seen a single example of that happening on any of the examples tabled in this forum albeit I dare say such has happened somewhere along the line.
Ironically, I have also previously suggested that the Cometic MLS gasket [of a sandwich construction] might despite its specific need for a smoother surface RA finish may in fact due to its presumably stiffer structural resilience offer better protection against this specific problem. I know GB has opined these things do not work - personally I have no experience with them whatsoever but one wonders why an outfit like that would offer such if they really do not work. Perhaps it boils down to what folks are comfortable working with. Simple fact the stock 928 head gasket is basically dinosaur technology in automotive development terms albeit it works perfectly well for the intended purpose. Unfortunately it cannot cope with this corrosion issue and I reckon that is something that was just not known about at the time of development. Let's face it Porsche's expertise was in air cooled vehicles and their racing vehicles that used coolant probably had water in them that was emptied out after every race so possibly no experience of dealing with glycol coolant long term strange as it may seem.
Ironically a stainless gasket in contact with an alloy head in the presence of an electrolyte like the glycol/water mix of the coolant has the potential to cause galvanic corrosion wherein the alloy will act as the sacrificial anode but this may not be a problem given the much greater mass of the block material when compared to the relatively small amount of material in the gasket.
Was your experience with the Cometic type gasket successful as a matter of interest?
07-19-2022, 07:17 PM
#18
Rennlist Member
07-19-2022, 10:02 PM
#19
Former Sponsor
I stock Cometic Gaskets, in several bore sizes, if you are interested in trying those.
After all, the original gaskets only lasted for 35 years. (And have not failed, AFAIK.)
After all, the original gaskets only lasted for 35 years. (And have not failed, AFAIK.)
Last edited by GregBBRD; 07-19-2022 at 10:03 PM.
The following 2 users liked this post by GregBBRD:
928FIXER (07-19-2022),
Kevin in Atlanta (07-19-2022)
07-19-2022, 10:18 PM
#20
Former Sponsor
Kevin,
My definition of "sandwiched" in the context of my comment is that the gaskets are now trapped between solid surfaces on both the head and the block sides and therefore the coolant cannot be entrained between the head and the gasket to cause the subsequent long term mayhem the 928 configuration experiences- doubtless they eventually fathomed it out as they saw example after example rot. I saw several sets of heads rot over here some 16 years ago that were cast off as scrap by the main agents as Porsche seemingly would not endorse such repairs. It never ceases to amaze me as to how folks blame coolant change intervals for this problem and then you see the transfer passages in the heads in immaculate condition not to mention the rest of the water jacket and the radiator show no signs of corrosion- how folks could think the problem was caused by the condition of the coolant or the coolant type/make is beyond me.(Yes, Fred. Just because the coolant manufacturers make different types of coolants for engines with different kinds of metal in them means absolutely nothing. Just "smoke and mirrors" to confuse the public. And, of course, it's so much cheaper for those companies to make and market multiple types of coolant, that they don't want to tell everyone that one type works for everything! That would decrease inventory and costs....for everyone. Can't have that!) Make no mistake coolants get exhausted as and when the pH drops below 7 and if and when that happens signiicant damage can be expected to commence at around pH6 but that would happen on all coolant wetted surfaces. I have never seen a single example of that happening on any of the examples tabled in this forum albeit I dare say such has happened somewhere along the line.
Ironically, I have also previously suggested that the Cometic MLS gasket [of a sandwich construction] might despite its specific need for a smoother surface RA finish may in fact due to its presumably stiffer structural resilience offer better protection against this specific problem. I know GB has opined these things do not work - personally I have no experience with them whatsoever but one wonders why an outfit like that would offer such if they really do not work. Perhaps it boils down to what folks are comfortable working with. Once again, GB gets tossed under the bus for making factual statements about what has occurred, many times. If you don't believe GB, simply ask Mark Anderson how many engines he's aware of that have had Cometic gaskets and leaked coolant...some so badly that they can not be started to see if the gaskets might seal when the engine gets hot. Simple fact the stock 928 head gasket is basically dinosaur technology in automotive development terms albeit it works perfectly well for the intended purpose. (Don't tell the people that rebuild 100's of thousands of American V-8's, every year, how terrible this technology is.) Unfortunately it cannot cope with this corrosion issue and I reckon that is something that was just not known about at the time of development. (Yeah, the German gasket companies had absolutely no experience with water cooled engines, before Porsche built their first ones. All of those BMW and Mercedes engines before 1978 were air cooled, right?) Let's face it Porsche's expertise was in air cooled vehicles and their racing vehicles that used coolant probably had water in them that was emptied out after every race so possibly no experience of dealing with glycol coolant long term strange as it may seem.
Ironically a stainless gasket in contact with an alloy head in the presence of an electrolyte like the glycol/water mix of the coolant has the potential to cause galvanic corrosion wherein the alloy will act as the sacrificial anode but this may not be a problem given the much greater mass of the block material when compared to the relatively small amount of material in the gasket.
Was your experience with the Cometic type gasket successful as a matter of interest?
My definition of "sandwiched" in the context of my comment is that the gaskets are now trapped between solid surfaces on both the head and the block sides and therefore the coolant cannot be entrained between the head and the gasket to cause the subsequent long term mayhem the 928 configuration experiences- doubtless they eventually fathomed it out as they saw example after example rot. I saw several sets of heads rot over here some 16 years ago that were cast off as scrap by the main agents as Porsche seemingly would not endorse such repairs. It never ceases to amaze me as to how folks blame coolant change intervals for this problem and then you see the transfer passages in the heads in immaculate condition not to mention the rest of the water jacket and the radiator show no signs of corrosion- how folks could think the problem was caused by the condition of the coolant or the coolant type/make is beyond me.(Yes, Fred. Just because the coolant manufacturers make different types of coolants for engines with different kinds of metal in them means absolutely nothing. Just "smoke and mirrors" to confuse the public. And, of course, it's so much cheaper for those companies to make and market multiple types of coolant, that they don't want to tell everyone that one type works for everything! That would decrease inventory and costs....for everyone. Can't have that!) Make no mistake coolants get exhausted as and when the pH drops below 7 and if and when that happens signiicant damage can be expected to commence at around pH6 but that would happen on all coolant wetted surfaces. I have never seen a single example of that happening on any of the examples tabled in this forum albeit I dare say such has happened somewhere along the line.
Ironically, I have also previously suggested that the Cometic MLS gasket [of a sandwich construction] might despite its specific need for a smoother surface RA finish may in fact due to its presumably stiffer structural resilience offer better protection against this specific problem. I know GB has opined these things do not work - personally I have no experience with them whatsoever but one wonders why an outfit like that would offer such if they really do not work. Perhaps it boils down to what folks are comfortable working with. Once again, GB gets tossed under the bus for making factual statements about what has occurred, many times. If you don't believe GB, simply ask Mark Anderson how many engines he's aware of that have had Cometic gaskets and leaked coolant...some so badly that they can not be started to see if the gaskets might seal when the engine gets hot. Simple fact the stock 928 head gasket is basically dinosaur technology in automotive development terms albeit it works perfectly well for the intended purpose. (Don't tell the people that rebuild 100's of thousands of American V-8's, every year, how terrible this technology is.) Unfortunately it cannot cope with this corrosion issue and I reckon that is something that was just not known about at the time of development. (Yeah, the German gasket companies had absolutely no experience with water cooled engines, before Porsche built their first ones. All of those BMW and Mercedes engines before 1978 were air cooled, right?) Let's face it Porsche's expertise was in air cooled vehicles and their racing vehicles that used coolant probably had water in them that was emptied out after every race so possibly no experience of dealing with glycol coolant long term strange as it may seem.
Ironically a stainless gasket in contact with an alloy head in the presence of an electrolyte like the glycol/water mix of the coolant has the potential to cause galvanic corrosion wherein the alloy will act as the sacrificial anode but this may not be a problem given the much greater mass of the block material when compared to the relatively small amount of material in the gasket.
Was your experience with the Cometic type gasket successful as a matter of interest?
Oh, never mind....
Continue on, with this great logic!
Last edited by GregBBRD; 07-19-2022 at 10:25 PM.