Can a thermostat cause engine to tap but not overheat on a hyundai sonata

Not likely. Bad thermostats usually stick in the open position, but when they stick in the closed or partially open position they will cause overheating. A thermostat will not have any effect on a ticking or tapping of an engine that is not overheated.

Ok so this is what you need to try no promises that it is going to work but worked for a friend of mine that had a ticking or tapping in his engine add some Lucas Engine Oil Stablizer to oil and let idle until ticking or tapping is gone. My friend had let his vehicle idle for about 45 minutes to an hour before the tapping and / or ticking went away.

Firebird gets a dollar for everyone of those he sells. Heck I may try it on my nearly new Dodge Ram Hemi that has lifter tick on startup. Firebird, if it works I'll send you a dollar. Higher grade of viscosity oil probably will do the same thing.

Nope only suggest to try it because it worked for me may not work for you but it is worth a try.

And by the way Bob did try a higher grade of viscosity oil before trying the Lucas and it still was tapping.

Tapping could be from an exhaust leak, too. There are sites on the web to help you identify an engine tick or knock. Try and determine what yours is being caused by.