I have a 2003 Mercury Mountaineer with a 4.6 liter V8. I recently had the AC condensor replaced. Since then, I occasionally will experience a warning bell and light that instucts me to check my gauges. When this happens the water temp gauge is pegged at its highest point. Seconds later the car goes into limp-home mode, and runs very slowly. I pull off the road,turn the car off and raise the hood. There is no sign of overheating. I get back in the car, start it and the temp is at normal - mere minutes after being close to armageddon! What gives? Do I have an air pocket that’s causing this, or is a sending unit bad. I’m worried that my car will cry wolf too often!
How do know that there is no overheating? Have you measured the temperature of the heads when this happens? Have you checked coolant level? When was the last time the coolant was changed?
Radiator was checked, cleaned and refilled last year. Coolant level is at max. If the engine was truly overheating I don’t believe it would cool down within seconds or 1-2 minutes. What’s your thinking?
I’d check the sending unit.
"If the engine was truly overheating I don’t believe it would cool down within seconds or 1-2 minutes"
It can do this if one of the heads is going overtemp due to an issue such as air in the cooling system.
Otherwise, it is possible that you have a bad temperature sensor or the wiring going to one of them is shorting. You just can’t be certain that this isn’t a real problem without checking the temperature.
"I’d check the sending unit."
Aren’t there three different ones to check, not just one?
are you checking coolant level in the radiator or simply the overflow bottle? must be radiator,if possible.