My Porsche had alien blood

[thstone]

The risk is whether the previous owner had fully flushed out the OEM coolant before re-filling with Prestone. If so, then there isn't any likely damage. But you will have to do a full flush (maybe two) to get all of the Prestone out before re-filling with the OEM coolant. This is because the Porsche OEM coolant isn't compatible with aftermarket coolants like Prestone.

Also, there is a chance that the green coolant was OEM. Porsche used green OEM coolant up until around 2005 and then switched over to the pink stuff. If the coolant in your car hadn't ever been changed (some owners believe that the coolant is lifetime and never has to be changed) there is a chance that it still had the green OEM coolant in it.

Bottom line: Flush out the green coolant completely and then re-fill with the pink OEM and you should be good to go with no worries.

[BirdDog]

As long as you weren't having over-heating problems, you could just keep using the green stuff (but if you do that use fresh stuff - you don't know how long it's been in there!)

If you plan to change over to the pink Porsche stuff you really need to make sure you flush out the green stuff. Make sure you turn the heat on to flush out the old coolant in the heater core. Mixing the green stuff with the pink stuff will produce a thick gel-like consistency wherever they come in contact that could impede coolant flow. Cracked heads are no joke!

Remember to cut the pink Porsche stuff 50% with distilled water. So 1 gallon of pink stuff = 2 gallons of ready to pour in coolant. The Porsche stuff seems like it's really expensive when compared to the aftermarket stuff, but Prestone is now sold precut 50/50. Cost wise they're not that different when you compare both cut 50/50.

If you are a PCA member, remember to ask your dealer for your 10% discount (most dealers do that).