Does anyone have an idea for a fluctuating water temperature problem? The water temp gauge operates like a windshild wiper. I started a thread on this a few weeks ago, but I have tried a few new things since. And the problem remains. System has been pressure tested, and no leaks detected. No sign of hydrocarbons in the coolant, and no indication of coolant in the exhaust. Thermostat has been replaced, as has the water pump, the temperature sending unit and the radiator. The heater core was replaced last February, and the radiator in April. None of these component changes made a difference. There is no appreciable coolant loss from the recovery tank, and no bubbles detected there. My mechanic gave me a copt of TSB 95-18-5 titled 'Temperature Gauge Fluctuations and Inaccurate High Readings'. It said to change the gauge and sending unit. As the sending unit had been replaced with a Ford part, I went for the gauge. Ford wanted $175 for a gauge, a bit pricey. So I got an entire cluster from the junk yard and installed the gauge. The fluctuations continue, but the swing isn't as severe, going from below the 'N' up to the 'M'. Mechanic used a thermal sensor to identify the temperature swing as 180-220. The heat output fluctuates also, indicating the water temp change is accurate. I was going to bypass the heater, but I've got to wait till spring for that project. Question is why does the temperature fluctuate? I am told it 'could' be the head gaskets, but I am hesitant to tear down the engine this time of year. If I knew for sure that is was the head gaskets, or the intake gasket, I would plan to change them in the spring. But engine has 145k on it, and it may be wise to rebuild or replace it, instead of just replacing the gaskets. Is there a definitive test, other than disappearing water or a massive leak, to point to the head gaskets? I have toyed with the idea of a replacement engine, rebuilt on the shop floor and just replaced on a weekend. But I would hate to go that route if there is another solution. Thanks in advance and any help and expertise will be greatly appreciated.