* Temperature Sending Unit: This is a very plausible culprit. A faulty temperature sending unit can give inaccurate readings to the gauge, making it seem like the engine is overheating when it isn't, or vice-versa (showing a normal temperature when it's actually overheating). This is a relatively inexpensive and easy part to replace. Highly recommended to check/replace. Get a new one from a reputable parts store, *not* a used one.
* Radiator Cap: A bad radiator cap can prevent proper pressure buildup in the cooling system, leading to overheating. It's cheap to replace and easy to test. Make sure the cap is sealing correctly at its rated pressure.
* Air Pockets: Even after a thorough flush, air pockets can remain in the cooling system, restricting coolant flow. There are specific procedures to bleed the cooling system of air; consult your repair manual for the correct method for your Intrepid. Proper bleeding is often overlooked.
* Water Pump (Again): While you replaced it, it's possible the new water pump is defective or not installed correctly. Double-check the impeller spins freely and that all connections are secure.
* Thermostat Housing: A crack or leak in the thermostat housing can cause problems even with a new thermostat.
* Head Gasket (Less Likely, But Possible): If all the above are ruled out, then a head gasket is a possibility, but it's less likely given the work you've already done. Head gasket failure often involves other symptoms, like white smoke from the exhaust, milky oil, or loss of coolant. Do a compression test and a leak-down test to confirm if this is truly the problem. These tests are more involved but necessary before considering a head gasket repair.
How to proceed:
1. Verify Gauge Accuracy: Borrow a known good infrared thermometer to check the actual temperature of the engine block and coolant hoses while the engine is running. This will tell you if the gauge is lying.
2. Replace the Temperature Sending Unit: This is the easiest and cheapest next step.
3. Check the Radiator Cap: Ensure it's holding pressure correctly.
4. Bleed the Cooling System: Follow the procedure in your repair manual carefully. This is critical.
5. Inspect the Thermostat Housing: Look for cracks or leaks.
6. Re-examine the Water Pump Installation: Verify it's working correctly.
Only after thoroughly investigating these points should you move on to the more involved and expensive head gasket diagnosis and repair. Remember safety first, work on a cool engine, and use appropriate safety gear.
