I have had a 1999 RL for about 6 months now and have had no problems. I was sitting in the drive through Saturday night and the engine started heating up. The gauge never went all the way up but it was running hot. After a short while it came back down again. It then went back up. and then down. Anyway my question is if it was the thermostat wouldn't it have overheated completely? I know the thermostat is an easy thing to change out but I don't think that is what it is.
Any help is appreciated
1999 Acura RL 104,000 miles

 

Burp the system. It's possible that you just have an air pocket inside. To do this, park on an incline or use jackstands to raise the front of the car. With the engine cold, remove the radiator cap and start the car. Have alot of water handy, either distilled or hose doesn't *really* matter. While the engine is warming up, massage the upper radiator hose while adding water to the radiator, keeping the water level at the point of overflowing. I'm pretty sure that after a few minutes, you'll have little bubbles rising from the neck. Keep doing this until the car's reached operating temp, and having someone rev it a little (below 3K) will help speed it up. Good luck.

~Cheers~

P.S. Worst case scenario is a BHG, but your symptoms indicate otherwise. Maybe slight seepage, but I still doubt it.