stratfordshark wrote:
This is a very timely thread!
When I last changed coolant couple of years ago I used Halfords Advanced which is an OAT (organic acid) which somehow I'd got into my head that that was correct for aluminium heads. In fact it's a no-no for 928s! The Advanced in fact says on label for post-1998 cars.
That Comma Porsche-approved coolant was not there when I looked last week when I bought new coolant preparatory to changing rad, so it must be new stock. It looks ideal and I'm pretty sure heard people refer to the VW G11 coolant which it is on Rennlist. I bought the regular Halfords which should be fine and friendlier to silicone seals than the OAT pink stuff.
OAT will work with most (if not all) aluminium engines (I'd use it in the Stag (an engine known for having alloy heads of a dubious material quality) if I was more sure of certain facts (read on...)). The post-98 label is more to do possibly with the construction of the radiators (which is another can of worms in itself). There has been quite a bit of debate over the years over whether OAT can deteriorate the solder on copper cored radiators, something which many a manufacturer continued using until the end of the last millennia (Rovers for example (MGFs/TFs depending on year will have different coolant specifications on many a manual!). Some reckon it does attack the solder joins, yet others believe it is only the older type of solder that it attacks (closer to pre-war stuff) since the type of solder itself changed).
My current 944 has OAT in it (and has done for many years) and AFAIK it has been fine. My previous 944 did not, and had a failed heater matrix: the only copper cored item in a 944's cooling system (it was leaking surely enough at the tank to core join, and it had been leaking for quite a bit of time over the years. The receipts did say that the car had OAT coolant in it but the coolant was fairly black in colour when I acquired the car (probably from several doses of K Seal etc...). An old MGB of mine however ran fine for a year on OAT which is a cooling system based on copper cored bits! No rusty coolant was present either.
OAT seems to last almost a lifetime though and offer superior corrosion properties (I believe OAT is more inert, whereas IAT (blue) coolants tend to react more). Either way, old Peugeot 306s I have owned with mixed metal engines have produced zero silt with OAT coolants, but there was the presence of silt with the blue coolants (especially when changed infrequently (hence probably why many a 306 owner recommends coolant changes every 2 years.). Even my Mondeo on 200k has spotless hoses inside (although that runs on Ford's own OAT coolant).
Anyway, that's my take on it. As for recommending a coolant, it's horses for courses. If you do have blue coolant though, ensure that it is changed on a regular basis. FWIW Porsche now only sell red OAT coolant for the 944 if you go to an OPC...