[Bob Kelly]

here's an idea..... when the bike is stone cold...... reach up under the right side fairing
and take off the radiator cap... then stand up and see if the coolant can be seen in the radiator.... I'ed bet money those guys at the bike shop never re checked it after filling it and it's only half full....
when the radiator is properly filled it will be up to the sealing ring just under the cap area.....
if it's low put in antifreeze/coolant that is a 50/50 mix you can do that with a garden hose on a funnel or a automatic transmition funnel from the auto parts store.
I seriously doubt there is a problem with the bike just incompetence of the bike shop.
Nobody cares for your bike like you do ! do it yourself even if it pushes your comfort level !
......with the radiator cap off and the coolant just covering the fins of the radiator you can squeeze the rubber hoses to force out most of the air in the system you might spill some coolant but it is worth it to get the air out.

Edit: also the bike has a thermostat so the bike has to be warm enough for the thermostat to open before you will see turbulence/circulation of the coolant so keep that in mind.



also when putting the radiator cap back on you push down and turn it 2 clicks push down and turn it clockwise as far as it will go ( about 1/2 ~3/4 turn) if it's not on tight you will over heat and boil out the coolant....( which might have already happened because of the shop trip)
....
so to re-cap take off the radiator cap fill the radiator , put the cap back on good and tight ( put it on and take it off a few times so you can tell where it SHOULD be!)
you can get to it without taking off the fairings but it's a pain !
then check all the fuzes under the seat and make sure all of them are good...one controls the radiator fan.... if it's bad it will over heat sitting there idling
....
the RX4 is a Super strong Tank of a motorcycle it will run practically forever !
but running it without coolant can destroy it in short order.
....
so test the cooling system and make darn sure it is working
after you do all the above test it to make sure it's working....
on my bike I simply put it into neutral and started it and let it idle and watched the temp gauge slowly come up.....till the radiator fan kicked on.... and I watched the temp go back down... then the fan turned off and the temp slowly raised again....
I don't know what kind of gauge you have on that bike but you should be able to check in the same manor...... if the radiator fan cycles on and off like it should you are good to go and it should not over heat again.... re check the over flow tank and make sure it's full for the radiator before you take it for a run....
....
hope that helps...
.....
Bob.......