I bought a USED 2004 Pontiac Grand Prix GT 3.8L, V-6 w 217,000 miles.
Last Summer it overheated for the firs time. After running a garden hose
down the radiator it cooled.
I has also seemed to overwarm at Drive Thrus. But upon resuming trip, the
gauge would resume the usual running temp.
I have had a rusty colored sediment/deposits, and upon changing the Head
Gaskets and Intake Gaskets, had a few plugged water ports. The Radiator
CAP was severely clogged.
Upon re-starting the engine, bleeding the,air out and checking the
Temperature was too hot, removed the thermostat.
Even still, the coolant, has OVERHEATED and now that it is cooled back
down, the UPPER Hose has collapsed.
Can the RADIATOR CAP cause all this?
Check your cooling fan to make sure it is functioning. It is probably an electric and could be failing to energize when your engine temp rises. A fan failure would cause the temp fluctuation you see between the rise in the "drive through" line and going back to normal at speed.
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