Does turning the heater on full cool the car down?

Check the rad for flow (is it EVENLY hot ALL over when the motor is fully
warm?)

Also check the rad fins for corrosion. They can corrode to dust in the
bottom middle portion.

If the temperature rise is steady and relentless, I would strongly suspect
the radiator. Airflow would be a possibility except now you have the fans
going full time, and you report it worse at high speeds. I would hazard a
guess the radiator has had tap water added at least a few times (don't do
that) - if so, the minerals have collected in the radiator and have made it
nearly useless.

The radiator could be rodded out, but I recommend replacement. The radiator
is near the end of the life expectancy anyway because of the plastic tanks.
And in the future use only proper coolant and distilled (deionized) water.

Duckbill's concern about the head being warped should be checked by the
simple field screening test: with the engine cold, remove the radiator cap.
Start the engine, pinch off the hose to the coolant reservoir and place the
palm of your hand over the opening for the radiator cap. If you feel
pressure steadily rising against your palm within a couple of seconds or -
worse - pulsations, the head will have to come off for repair of the head
gasket or to be milled. A shop can do a chemical test to confirm the
problem. But I don't think that's likely. Head warpage comes from the head
not having coolant; the temperature soars. Assuming it has always had
coolant present even if the coolant is at the boiling point, you should be
okay.

Mike

Sounds to me like you need to check for the presence of carbon dioxide in
your cooling system. Either a blown headgasket or broken head bolt or both.

David Short
Acura God

i totally agree with Acura God  get it checked out that way you will no where you stand if i had to guess i would say you have a leaking head gasket"  =

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johnin