I've recently replaced the water pump and it has a fairly new 160* thermostat. It runs at about 170 on a 50-60 degree day, 150-160 on a 40 degree day, but as I was driving home from work today (mid 60s out), (which I was driving about 55-65 the whole time), I noticed the temp slowly rising as I was driving. It went slightly over 180*, and as I came to red lights it was go up bit by bit. By the time I pulled in the driveway it was about to hit 200*.

My concern is that it may not stop going up if I was on a longer drive, does anyone have any idea whats going on?

It used to run at 210* when I got it from the previous owner, but I wanted to run it a little bit cooler as I had it torn apart. Thanks!

 

Sounds like a radiator getting plugged up. Have you done anything with it?

 

I had the coolant flushed when I first got it, and it generally ran at a steady 210* even when it was around 90 degrees out. I had a handful of problems last summer (head gasket blown, mismatching pulleys) and finally got it up and running for spring.

I was hoping that wasnt it :/, but I figured it probably needed to be changed sooner or later. It's atleast 10 years old, there's small dents in the fins from taking the fan off/pulleys/pumps/tools slipping/dumb mistakes, but it doesn't look like any of the core lines are damaged. I'm not 100 percent sure if its the original 307 radiator or not.

 

Sounds almost normal to me. Please note that a thermostat is for setting the minimum operating temp of an engine, the maximum is set by your cooling system capacity. Your engine came with a 180 degree thermostat, on a warm day in traffic it is not out of the ordinary for your water temp to go up to 210-220 or higher. What it's suppose to do as you drive it drop back down to around 190-195. Now if your temps are getting to an extreme at idle I'd check to make sure your clutch on your fan is functioning correctly.

 

You could have a steam pocket. Did you burp the cooling system.

 

I agree. Almost every "slow to overheat" issue I ran across was a radiator issue.

 

Is this a factory gauge? If so, I would be surprised if anything is wrong. I replace radiators, fan clutches, t-stats, temp sending units etc on my 87 Cutlass trying to solve the same problem you are having. I finally installed a cheap Sunpro temp gauge, figured out when the dash gauge reads 220 the engine is actually running about 180!

 

From what you posted, it sounds as if nothing has changed (temperature wise).

Why exactly did you think it would run any cooler now than it originally did?

 

An old man at work who told me a 160 thermostat would make it run cooler. lol.

 

the p/o added an aftermarket gauge, the stock one shows the same readings as the aftermarket one.

 

Have you driven it for an extended period of time to see where the temp levels out? The 210 that you used run is normal if it had a 195 degree thermostat in it before. It's going to rise in traffic but should drop back down as you move along. If it's getting abnormally high in traffic or at idle, I'd replace the fan clutch if equipped.

 

Being a late model G body, with a converter, it originally had a 195 thermostat, and changing it to something cooler, will help, unless the converter is beginning to get clogged.
If it is original, take it to an exhaust shop, and have it checked.
If partially clogged, you've two choices - replace or eliminate.
Might also check the lower hose for the spring that belongs in there - is necessary to eliminate collapsing.