While rebuilding my valves, I noticed that 4 out of 6 exhaust valves on one side of the V6 engine were leaking after lapping and I had to relap them. I determined that by doing a water test. I am guessing they were leaking even before (IOW that the leaking wasn't a result of a poor lapping job) which sounds tenable because the exhaust ports looked like a mess before I cleaned them. The fact that none of the intake valves leaked led me to a conclusion that exhaust valves take more heat so they are more likely to need readjustment.
But what are some effects of leaky exhaust valves? E.g. I underwent the complete head gasket and valve rebuild procedure because my engine was overheating and the head gaskets got fried. My speculation was that was because of a stuck thermostat that caused overheating. But could it have been due to leaky exhaust valves?