2000 Dodge Caravan Heat Problem

When idling, my 2000 Dodge Caravan heats up properly and the heat works well. Once I start driving, the indicator on the temperature gauge drops and the heat stops working. If I stop moving, everything seems to work well.

Is the thermostat the likely cause?

Probably.

The thermostat's got my vote.

Clarification: A thermostat installed upside-down would most likely cause your engine to overheat because the side of the thermostat that causes it to open is on the cool/radiator side of the thermostat and not the hot/engine block side where it should be. So a bad (upside-down) installation most likely is NOT causing the problem.

Thermostats most likely fail due to scale build up that inhibit the thermostat's plunger from properly opening and closing to maintain a *constant* engine block temperature. Sometime, thermostats will freeze in the full or nearly full-open position - this would precisely explain what is happening to your Caravan.

You didn't mention it, but I would also bet that it takes an extra-long time to warm up your Caravan in cold weather too - with the thermostat always open, the engine would need to heat up ALL coolant in the system, not just the green stuff in the engine cooling jacket. In EXTREMELY cold weather, your Caravan might NEVER reach normal operating temperature.

If you flush your cooling system and completely replace your coolant at least every two years, you should be able to drive your Caravan for 10 years or 200,000 miles without a problem. Maybe more.

On the other hand, constant/repeated and daily radical swings in engine block temperature can cause more serious problems. Since the engine block and everything bolted to it are generally made of different materials, these different materials have a different "coefficient of expansion" - they expand with heat and contract with cold at different rates and speed. The added stress of engine block temperature changes *while operating* can be catastrophic.

You could develop leaks between two gasketed components made of different materials over time - like the mating surface between the water pump and the engine block, for example. Contant swings in temperatures can literally "ungasket" one component from another. Get that thermostat replaced right away and never, EVER go more than two years between full cooling system flushes and replacement!

Your water pump will last longer too - because new coolant usually contains lubricants that prolong water pump bearing life. These lubricants, like the coolant itself, breaks down over time and becomes less effective. Good Luck!... :)

Thanks for the responses. I am changing the thermostat and flushing the cooling system today.

Did it work? I have '95 Voyager with similar issues. Would love to know if you had success. Thanks