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2000 f 150 V6

2000 F 150 Coolant temp gauge fluctuates wildly

Check coolant in radiator. When was the last time the coolant was flushed and filled?

last week, Flushed then replaced radiator, thermostat, new coolant

There could be a connection. This is usually the result of low coolant level or air in the system. The person servicing the coolant system may have left air in the system or left something loose, causing the coolant to leak out. This, of course, bars the possibility that you had the coolant system serviced to try to correct this issue. Is this a new symptom, or has it been going on prior to having the cooling system serviced?

I can think of two things other than a coolant leak or air in the upper hose.

  1. loose/poor lead connection from the temp sender, (could have been bumped durring service.)
  2. loose/poor battery lead, esp. ground lead from battery.
  3. (bonus point) loose lead conn. at the temp indicator under the dash. or between sender and indicator.

There’s probably air trapped in the cooling system. To remove any air, do the following.

Get the engine up to operating temperature. With the engine idling, loosen the upper radiator hose clamp. Take a small flat bladed screwdriver and insert it between the upper radiator hose and the radiator hose neck. Allow the engine to idle until the air stops sputtering out and a steady stream of coolant starts coming out. Remove the screwdriver, tighten the hose clamp, and check the coolant level after the engine cools down.