Yep, he ran green coolant
, suposedly the stuff that is good "for all makes" "even cars with aluminum heads!"
I plan to have my indy do a coolant flush, new thermostat, and then refill with MB coolant. For the regular coolant additions I plan to use Zerex G05 50/50. Then I'll see if the temps cool down. PO said he replaced the radiator a couple of years ago, and indeed, the Behr that's in it has a manufacturing sticker dated 9/06, so it's not too old. Wonder if him running the green stuff could have ruined the radiator in that time, though. In my last car, I always ran the MB stuff so I don't know what damage green coolant does over time.
Interesting suggestion that I try a lower pressure expansion tank cap. The head seems to be just barely leaking, so maybe running with a lower pressure might cause it to stop. I'll try that.
Again, I'd like not to dump $2K into the car if I can help it, but I really don't want to risk blowing the motor if that's a possibility, especially after my experience last month with my former W124 300D. I think I'm spending more time watching the temp gauge than the road, however
. If the temps come down with a good flush, new thermostat, and the proper coolant, maybe, just maybe, I can clear the Rockies with that head gasket as is.