Hi everyone. I'm 21 and just joined the forum in an effort to figure out what is wrong with my car. (I think I initially posted this in the wrong forum category, my apologies)

I've got a hail damage special 2002 Impala LS Sport with the 3800. Its currently got 174,000 miles.

First, Since I bought the car (year and a half/ 30,000 miles ago) its had issues with the temperature. When driving highway speeds it will only heat up to 160 degrees. It will stay steady at 160. If I stop and it idles, the temperature will rise to around 190 or 200 degrees where it will stay until I start driving again. Then it goes back down to 160 degrees. I verified that the temperature gauge is accurate with a code reader.

I replaced the thermostat when I bought the car hoping that would fix the issue but it didn't.

Secondly, Sunday I hit a large snow drift on the gravel road which filled the engine bay with snow. After cleaning the snow out of the fan I continued driving. However, since then my temperature gauge is acting up even more. The temperature fluctuates with both my speed and if I am going up or down a hill (I'm not full of it, it reads lower at the top of a hill and hotter in valleys). Is this connected to getting my engine bay full of snow or a coincidence?

Sorry for the long post.

Thanks in advance for the advice.

Have you checked to see how much coolant is in the system?

When was the last time the system was flushed? Anything ever mixed with the original Dexcool?

I'm also wondering if your water pump is on its way out.

Cooling fans coming on?

It acting/ sounds like the thermostat is stuck in the open position. Even new does not guarantee and good working thermostat now-a-days, cheap crap.
What brand & temp rating of thermostat did you install?
I used a Delco 195 degree and drilled a small hole in top edge, to allow for air bleeding.
Since it'* easy to replace try another one, Delco 195 and see if that helps.

Yeah, I'm surprised the old thermostat did not set a P0128......

Could still be a bad thermostat.....and like Mike has suggested, you could have an air pocket in the system, causing temp swings......so check radiator and reservoir levels, first thing in the morning, BEFORE the car is started....

As also suggested, make sure the cooling fans are working....

you know the fans and pump and rad are working properly because it would overheat. its seems likely a bad thermostat. people get bad new ones all the time. also have to fill it with the bleeder open.

He mentioned when stopped at an idle it heats up. When he starts driving again it cools downs. Sounds like the cooling fans aren't working or possible water pump failure.

heats up to normal temp then goes back to way too cold when moving

If that'* the case, it'* a bad therm and should set a P0128.....just funny that a replacement therm would cause the exact same problem.....but there are some cheap thermostats out there...

Whenever I have a P0128, and the car is idling, engine temp can rise to normal temp, because even though the therm is slightly open, it has enough of a restriction to slow the flow of coolant......but now when you raise the rpms on the highway, there is more flow through a very cold radiator and that coolant can drop into the 160-170F range, quickly.....I just do a quick road test with a P0128, and if I see the temp drop like that, I know it'* the therm opening too soon....

Have read online a lot of cases where new therms are a problem, but I haven't run into any of them....just lucky I guess....

i think its just people who buy cheap thermostats, i have not had one fail either but i imagine its because i just go with a good one from the beginning, even the good ones are relatively cheap