Anyone seen this problem?

I have a stock thermostat and a new water pump (old one leaked; note: this problem did not occur with old one w/the 160Tstat). When I'm running on the street (up to 45mph in 3rd or 4th gear) temp gauge is at 185 (approx). But when I'm on the freeway (75-80mph in 6th gear) the temp goes up to 210-215. Sometimes when I get back on the street and back to 35-40mph the temp drops back to 185.

Could this be a water pump problem? This is really screwed up.

Before I switch back to the 160Tstat, I'd like to solve this problem.

 

it is a flow problem(air or coolant)

check innfront of the rad for debris(between the rad and condesor as well)
is your air dam in place?
if these are good, your rad is probably got some clogged tubes, and a regular flush probably won't fix it(also, new rads are pretty cheap now a days)

 

Yeah, the air dam under the nose is in place. I wonder why at low speed it cools fine, but at highway speeds it doesn't do it as well?

I looked at the rad from the front and the fins are clean. I've had a flush done a couple of times over the last 3 years (is that good enough?). By the way, I programmed the fans to turn on between 205-213 via the Hypertech programmer.

This is puzzling.....

 

Ok, here's the scoop. There were 2 problems.

1. The radiator cap was not holding pressure - I heard it fizz when the engine temp reached normal operating temp. Fizz came from the tube to the coolant reservoir.

2. The air dam was being shoved back at high speed so it was less effective at the higher speed. At low speed it held its shape/angle so cooling air passed thru the rad no problem.

The fix:
Got new rad cap.
I installed 2 supporting wires to help the air dam keep its angle during high speed and that seemed to have done the trick.

Hope this helps someone.