I have a Oldsmobile Silhouette with 190k miles. Here is a brief relevant history:
120k, radiator was dented. Slow leak. Topped off every couple oil changes, no issues.
188k: One time the temperature gauge spiked very high when I came to a stop for a minute. Previous speeds were not out of the ordinary or high… city driving.
Now: Cold may have factor. Car spikes in temperature intermittently, but more so when driving slowly. Temperature stabilizes to normal if I turn off the engine for a minute and restart. I have seen the overflow tank bulge during a more serious overheating event.
Strange observation: When cruising at 30 mph and watching the temperature gauge, the heat blows ice cold normally. When temperature gauge rises to a few ticks above “normal” (mid-range), I can feel heat and the temperature shoots back down to a tick or two below normal.
Strange observation: Grade of road or hard braking seems to sometimes trigger relieving the overheat. The temperature gauge doesn’t go past the red, just right up to the red. If I run the car at idle during an overheat, it seems to recover.
MY best guess and hope is that the thermostat is intermittently sticking. What do you think? I’m considering replacing it myself. The problem seems to be better when the temperature was over 37F one day a couple weeks ago. Most of these symptoms have been in this 0-25F weather we’ve been having.
Thanks for your help.