GregBBRD

Wait until you see the pictures.
The deterioration of the head gaskets is very concerning, to me.
While there are not gaping holes, there is definite deterioration of the gasket, with corrosion coming from under the paper...making little "corrosion volcanoes" obvious. Not what I would expect to see at 3 years and 40,000 miles.

I generally use factory Porsche coolant in all my new engines. And to save clients a few bucks, I generally use the G-05 coolant in any used engine that I have no history of....since I have no idea of what coolant has been used, in the past, and it seemed like a reasonable choice.

I'm rethinking that, now.

worf928

Maybe we need to find a Rennlister than can do a chemical analysis of various head gaskets (NOS if we can find one and a new one.) The thought that new V-R/Porsche head gaskets turn into mush after 50k-miles is not something I want to think about.

I will go to sleep tonight knowing that I've only ever put G-05 in one 928 at the owner's insistence.

jcorenman

Pictures or it didn't happen: Head gaskets were under attack also. This first pic is the "bottom sides", exposed to the coolant passages surrounding the cylinders:




Here are the "top sides", against the head. Note the ribbons of sealant, which isolate the oil drains and head-bolts from the coolant, but not the space surrounding the fire-rings. And note the holes along the bottom edge, "coolant vents" into the space between head and gasket.
Also note the yellow / reddish corrosion stains, which correspond to the stains and corrosion on the head. And mostly on the one side:



Here's a "crusty" area:


Here's a close-up of a corroded spot. The gaskets are an outer layer of some sort of resin on either side of a metal mesh layer, which was corroding wherever there was a break in the outer layer. There were were numerous "bumps" where this was happening. Here is one where Greg picked it open with a knife. The metal layer was toast:



Every place there was any defect in the outer layer e.g. where they stamped "TOP" (or "Victor Renz") was corroding internally and starting to raise a blister:




I need to be clear on a couple of points:

1) There were zero external symptoms, it was just quietly corroding internally. If it hadn't been taken apart for other reasons, we would not have known for many years. These engines are tough, even when they are slowly being nibbled to death.

2) And this damage is minor, a quick shave and new gaskets will take care of it, and a more suitable coolant will hopefully prevent a recurrence. We may have dodged a bullet. However, we do not intend to disassemble and check it again in another three years. This is simply a rare opportunity to see what happens with a fresh engine with a popular coolant in a relatively short interval.

3) This is not meant as a criticism of anyone. If you chose a coolant more wisely than we did, then take solace in that. If you are using G-05 for a 928 engine then I would kindly but strongly urge you to reevaluate your decision. But it is your decision, and please feel free to ignore this advice-- it may be completely wrong.

4) No corners were cut on this engine, and any bad decisions were ours, not Greg's. Our shared passion is 30-40 year-old cars, and things change. We learn, we adapt, and we gather stories to tell the next time we get together.

Cheers, Jim

Kiln_Red

Thanks for sharing your experience, Jim. Sorry for your misfortune. There is a always a positive takeaway, and in this case I think it is that everything should be repairable based on observation of the cylinder heads.

I'm sure it's been discussed here before and I probably missed it, but I give validity to the voltmeter "acidity" test. When I was still working in Nashville, I worked alongside a really bright mechanic that used his voltmeter as a first step for cooling system evaluation. He said you could just about take it to the bank that if any coolant went to 600mV or more, there would be a cooling system failure in the near-term unless the coolant was changed immediately. He didn't believe in flushing a cooling system, in this event, as there would be higher risk to advancing potential HG defects. Also, if the weather were right and the customer could be trusted to follow-up, he actually changed it twice (short interval) and just filled the system with h2o the first time. That said, it was rare to hear that he actually observed 600mV or higher.

I have never used G05 because it was one of the coolants that would occasionally go to 600mV or higher. This was 10 years ago FWIW. Perhaps the voltmeter coolant screen is no more than a silly pseudoscience, but I have seen it give reliable indication of cooling system health enough that I am satisfied to rule it out as just coincidental.

dr bob

Can you share a little more on the "voltmeter acidity test" please? I watch the pH carefully, keeping it >9.5, and keep on a two-year coolant change protocol. I've been using and recommending G05 for a long time though, and it's that time again, so this may be the perfect time to adjust the coolant choice.

Kiln_Red

Using a DMM to check coolant:

Note: Set the voltmeter to its lowest range instead of 20V as the video suggests.

Dr. Bob, it's said that this is just an alternative way to evaluate pH levels.

SwayBar

A very interesting development, thanks to everyone for sharing!

Tomkat80222

Ouch! I did the volt meter test and got .14 volts from G05 that’s been in for about a year. It will be very interesting to see how bad the damage is when Sean pulls this engine apart later this year. During the 900 miles I drove to Telluride and many redline traffic passes I lost 2 pints of coolant with no external signs of coolant.

HenryPcar

Anybody have the same problem with Zerex G-40 which I'm using at the moment ?

Kiln_Red

140mV isn't ideal, but not completely indicative of impending or present doom. I would definitely change the coolant though. You don't want to see more than 60 or 70 mV.

bureau13

I'm going to do that voltage test this weekend. If I decide to change from the G-05 to something like Pentofrost NF, is there going to be an issue with G-05 mixing with the new stuff? I'm thinking about Dexcool allegedly turning to jelly when put in over some residual "green stuff."

HenryPcar

The industry standard for checking electrolysis is with the engine running not to exceed .3volts. BMW, Mercedes and Porsches all have similar guidelines. Even with fresh coolants, it would have exceeded .1 volts for sure.

Kiln_Red

My 928 is sitting at 60mV, so less than 100mV (0.1V).

Jim Morton

Thanks to all for posting this information. It ties in with some concerns I have been having lately.

Does anyone have specifics for how the G05 coolant is incompatible ?

Also, I reviewed the Pentosin data book for the differences in the their various offerings. Didn't really make. There were different thermal coefficients and boiling points listed but why would an aluminum engine from Germany (BMW, MBZ, Porsche) have different needs from their Asian counterparts ? The Pentofrost "Blue" did seem to have the best thermal properties, so why the red and purple variants ? Curious...

Comments welcome.

worf928

Probably. The one 928 for which G-05 was requested, I ended up doing it twice because I'd forgotten about the old coolant in the heater core. I don't know what was in the heater core, but I didn't like what I was seeing.

If changing to or from G-05 I'd do a flush with water (heater on full blast too) to get all of it out. That's what I ended up doing: draining the G-05, a couple of heat cycles with H20, and then new G-05.