2001 Olds Intrigue overheating problem

I was sitting in my car on lunch break. I noticed the temp gauge was higher than normal. Then I noticed a little steam coming out from under the hood. When I checked, there was antifreeze leaking out from where the tube connects to the overflow tank. It didn't look like there was a hole in the tube, it was squirting out right where the tube connects to the tank. I turned it off, and had to go back to work. I'm not mechanically inclined. When I got off work, I put a bottle or Bars stop leak in and filled it back up with antifreeze. Started it up, didn't seem to be leaking. Drove it home. Any time I am idling or cruising, the temp gauge will go up to the 3/4 mark , when accelerating it will drop to between 1/4 and 1/2, which is where it normally was. Anyone know what would cause this? What should I start with? Any help is appreciated, thank you.

Fix leaks, don't seal them, it leads to other problems...

Could have an air pocket in the engine, formed by the leak...

You should really install a new coolant surge tank (and new cap), sounds like yours is cracked. Easy job, two nuts on top and it slides up. The system needs to be totally sealed to build pressure and work correctly.

You might also have air in the system now. Turn the heater to max and let the engine come up to temperature so the thermostat opens. With the coolant fill cap off, take your hand and rev the engine at the throttle body. At the same time, take your other hand and squeeze on the upper radiator hose to feel any bubbles moving through. This hose should also firm up as your rev the engine if everything is working correctly.

Put the cap back on tight and let the system build pressure. Open the bleeder screw on the radiator (on the battery side, next to the headlight. It's a valve, don't unscrew it all the way). Leave it open until you see a fairly steady stream of coolant coming out and close it.

If you're still having problems, make sure your cooling fans are coming on. If they are, you may be looking at a bad water pump, plugged radiator, or leaking coolant crossover.

Also, I'd flush the bars leak out as soon as I got a chance. That stuff will do you no favors.