What was the original reason for the HG replacement? Couple of things I can think of off the top of my head. You didn't get the system bled correctly or, and I hate to say it, the HG job did not take. Are you SURE it was the HG's at fault originally? Sometimes a crack forms behind a cylinder liner and the only way to fix that is to remove the liner, weld up the crack if possible and install new liner(s). At the very least, you need to get your coolant/oil analyzed for contamination. Otherwise your just guessing.Just completed head gasket job, as earlier posted, this morning as I was on my way to work my 02 temp gauge started rapidly rising. I pulled off and the expansion tank was pissing coolant from the overflow tube. I had been on the road for about 20 minutes with no issues. I'm at a loss right now.