It almost seems like low coolant, but I'm sure you've looked at that already.
But here's something nobody ever seems to look at - The water pump belt, tensioner and cam pulley.
The tensioner can become frozen from dirt and road salt. From there, it no longer provides tension to the belt. The belt begins to slip. I recently had to replace a pulley, belt and tensioner on a '94 STS (who's trunk is held shut with a tie-down strap for an indication of the type of service this car has had) because it had been slipping so much for so long that the drive pully on the left intake cam was worn to the point where there was nothing left for the belt to ride on. The car had similar symptoms to your car. It heated up at idle. It did not overheat to the point of boiling coolant out, but it would get quite hot, even in the lower tempratures we've had in December in this area, which are far warmer than normal. It was getting up to 230 or better, which is not out of line but is hot for only short stops in 30 degree weather.
If the car isn't boiling coolant out of your car, you can be pretty sure that it probably isn't head gaskets.
And if it is head gaskets, you asked the question of whether it's worth it to do that job on a car with 127K miles on it (going from memory here) Well, I just did head gaskets on a '98 STS with 200K on it and I feel it was well worth it. The car has been well maintained in all other respects, so I expect it to go at least another 100K miles, mostly trouble free. You will need to do what works for you, but unless the car has been abused and neglected all its life, it's still a fairly new car in most respects.
I have a 02 Deville & the radiator temp always goes 2 the half way mark never once over it. My question is that's normal dead center?
4 got 2 mention I have a digital dash board. If that even matters it doesn't have actual temp readings. Half way mark guess n about 220 degrees?
Not sure about the digidash, but if that is where it always sets, that's the normal position. I would expect it to be about at the half position.
Cool thank u!
Gauge pegs out in the red
Not positive but I think center or just below center seems to be normal for mine, then it hits red and the alarms go off.
Update on the 98 Seville, drove it for the first time since I have had it in the show. Got the shop to order the testing equipment to test for exhaust in coolant. Didn't take the test long to change the bad color. If I keep the car I think it will just get a new GM motor. Then pull this one apart and check the head gaskets. I found some GM head gaskets at a very good price.
I agree with Mark in post #17 - that's a good insight. I had the bearings on the water pump tensioner pulley seize - the belt made a slight squealing sound upon cold startup, but that was it. After about 30 seconds or so, it quieted down - the belt kept moving, and so did the water pump, but the belt was slipping on the tensioner pulley. Needless to say, I replaced the pulley (rest of the tensioner was fine), and the belt, and all was well again
I think you might find it advantageous to simply do gaskets on your engine.
Be mighty sure it really is head gaskets first, though.
And head gaskets aren't all you'll need to do the job. They are about the cheapest part of the job, though.
You WILL want to get the stud kit and do it right. For the amount of work involved, there is simply no other way to do it than the right way the first time. If you don't do it the right way the first time, then this won't be the last time you have the problem.