The new to me '91 Carat I recently bought had a reputed overheating problem.
In trying to suss the cause out, I noticed that it runs steady with the
coolant temp needle over the LED or a tiny bit above, even though I had bled
it properly a couple of times.     This bothered me as my '84 always runs
with the needle below the LED.

It had the wrong antifreeze in it so I decided to flush it and change to
phosphate free.
I disconnected the radiator hoses from the engine end of the long plastic
tubes, jammed a hose it there and back-flushed the radiator as hard as my
leaky connection would allow, until the green was out and did the same the
other way around.   I then took the thermostat out and flushed everything
else out with the garden hose everyway that I could.   The thermostat is
marked 80.
I put in the new antifreeze, filled it up, bled it a couple of times and now
it runs steady with the needle below the LED, no matter how hard I drive it.

I swear just back-flushing the radiator as hard as my hose would let me, made
all the difference.

If your cooling system seems a bit marginal and overheats in traffic etc,
just try flushing the radiator out.
Its perhaps an old fashioned idea but it might just be your problem !

cheers,   Steve Cotsford