Have a 2003 Mazda MPV. Check engine light came on, temperature dropped down to cold, had the check engine code ran and came back as PO126 which is a thermostat issue. When idiling, has a normal operating temperature, if we drive less than 1 mile the temperature goes down all the way to cold. Have replaced the thermostat and then thought we got a bad thermostat, replaced it again and it does the exact same thing. Not leaking antifreeze anywhere, ran it and added antifreeze, overflow reservior is at full. A friend who is a mechanic put it on a scope and said the operating temp and guage coinside. He said it was a thermostat issue, which we told him we had already replaced and he was perplexed.