Drove on all electric mode for 8 months. No gas.

Welcome. With short trips and frequent charging, you might go for years with a slightly blown head gasket, as long as a cylinder doesn't fill up with coolant and bend the crankshaft! I've got 3,377 miles on this fill-up with 3 bars remaining on my 2012. The indicated EV range is 10.6, but I'm sure that the estimate reflects recent air conditioner use. Fortunately, no head gasket problems. Here's my favorite head gasket graphic, showing six different areas the gasket can fail. The best failures are when oil or coolant are blown to the outside of the engine. Messy, but no driveability symptoms and not fatal unless you run out of either fluid.

 

since we got home from florida on 03/15, i have driven over 2,000 miles. 95% ev. and the 5% hv is me trying to burn off the tank of gas i foolishly bought, think i was going somewhere.