98 Sable - Overheating

I have a '98 Mercury Sable w/ V6 overhead cam.
Back in December 2003 I had the radiator replaced because it was leaking. Everything has been grand. No problems whatsoever.
Last month, the temperature suddenly climbed very quickly. It was the water pump. A couple of the fins on the pump had been knocked off, I guess from age. The car has about 150,000 miles on it, and that was probably the original water pump.
Had it replaced. It's been, oh, a couple of weeks or so and the car's been running great and at a normal temperature.
Then today, I left the house and I drove along. Car was running at a normal temperature for about 22 miles of highway speeds at anywhere from 60 to 70 miles per hour, depending on traffic. But about 22 miles into that trip, the temperature started creeping upwards. It was climbing slowly enough that I was able to get to a decent stopping point with the temperature at about 70% of its maximum.
I let it cool off for a while. I removed the thermstat, thinking it might have stuck, so I could get the car back to the house. I would basically be backtracking my earlier trip.
This time, I drove slower, about 55 miles per hour until I made it about 17 miles into the trip, then seeing it was doing okay, I moved it up to about 63. Still doing fine. I reached a stop light, did my duty, then took off again at a normal clip. The temperature started climbing. By the time I was half a mile from the house, it was time to shut the car down at about 90% of its maximum temperature.
I let it cool down for about 20 minutes. The temperature gauge returned to normal and I drove it on home and parked it without an increase in temperature.
Based on behavior like this, and keeping in mind the key points that the radiator was replaced in December 2003, the water pump was replaced in June of 2004, and I had removed the thermostat, what's your best guess as to what's wrong here?
Damaeus
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In posted on Tue, 06 Jul 2004 03:29:33 GMT:

I checked the fans, too. Both of them work, and nothing has flown up against the condenser.
Damaeus
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I have a 98' Taurus 24V DOHC with 139K miles on it that has a similar problem although I have not replaced any of the HVAC components. In another auto forum it was suggested that I check for the restricted air flow through the condensor and then the radiator. The thermostat could be at fault, not opening fully. The water circulation through the radiator/engine could be a problem. Have checked profesionally or drain and pour water through radiator and see if it comes out the drain plug fairly fast or better yet disconnect the lower radiator hose and pour through and it should come out nearly as fast as it goes in, within reason. Take the serpentine belt off (may as well replace as long as you're that far if it hasn't been replaced lately) and check the water pump. Should be no up down movement or side to side movement. The A/C kick out switch could be faulty too as well as other possibilties. If you find something I would be interested.
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In posted on Tue, 06 Jul 2004 13:56:16 -0400:

Well, in my case, it was a plastic bag. They pulled the bag out, put my new thermostat in, test drove it, then sent me on my way. However, I got about 1/3 of the way through my 38.5 mile trip to work and the temperature started climbing again. I stopped, coolant boiled out of the reservoir. I waited for a while, then drove it back to the nearest town, maybe 4 miles. I ate something, went back and refilled with water. Drove it home. Now I'll be taking it back to the garage in the morning to find out what the heck is happening.
My dad thinks this new radiator is clogged up. He thinks when it got hot the first time, it might have broken a bunch of stuff loose that clogged up the radiator. Kind of a shame, too. Seven month old radiator, possibly ruined. Seems like they never do work right again by just having them "rodded" out.
:-(
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In posted on Thu, 08 Jul 2004 06:24:26 GMT:

I'm not liking this so far.
I talked to the guys at the shop yesterday at 10:30am. They were looking at it but I still don't have the car back yet. I sure hope I'm not being charged $65 an hour for this. That would be $390 in diagnostics.
I never believed in prayer, but I'm starting to consider doing it just this once.
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In posted on Tue, 06 Jul 2004 03:29:33 GMT:

Here's what I've already mentioned:
new radiator new water pump bidirectional flush of cooling system pressure tests
Here's what's been done since we last met:
test for blown head gasket -- head gaskets are fine replace water pump and thermostat AGAIN checked routing of serpentine belt it's not a freeze plug - no leaks more pressure tests
Still -- the thing runs normally for about 30 minutes or so, then the temperature starts climbing again.
What they're now checking:
new radiator cap lower radiator hose to see if it's collapsing
We're running out of options here. Is there something we're missing? Why would a car run at a normal temperature for 20 or 25 or 30 miles, then suddenly start climbing so quickly, especially when the cooling system is full, but there are no leaks?
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try it witout the termastat
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