For the past month my temp gauge constantly moves between the 'N' (where it always normally stayed) and the 'M'. It does this very slowly back and forth while driving. I changed the thermostat, but it still does the same thing. With the reading I've been doing, I'm thinking that it may be a faulty ECT, but don't really know. Any Ideas?

Thanks.

 

The Ect has no bearing on the temp gauge .What truck & engine do you have ? Give the cooling system a good going over , check for dirt & debris in the A/C Condenser , check for leaks around the hoses & the water pump weep hole . How old is the coolant ? Check the fan clutch operation , make sure its engaging when it needs to

 

 

Would help if we knew more about your vehicle...

Other things that might be wrong are: 1)Fan clutch(does the fan noise change while driving steady speed?) 2) Are there any hoses that are getting soft and mushy? They may be collapsing while the engine is running at speed and then opening up when you slow down. You can test that by checking under the hood and watching the hoses as you change the engine speed. It takes a minute or two to see this happen so be patient. Keep it a high speed for awhile and check hoses. 3) Maybe your gauge or sensor is going bad, not sure how to check but would guess you could check shop manual and see what type of meter reading you should see in steady state while checking across the sensor and gauge. I would expect the readings to be steady if there is no problem with either and really a problem with the coolant temp itself. 4) A wild chance, I have had thermostats that were bad right out of the box, might be worth a check just for fun once you eliminate other things of course. 5) I assume your cooling system is clean, if not, maybe there is some gunk floating around that is clogging and unclogging. 6)Maybe a belt is slipping.

There are probably other things to check too, but these have all happened to me with various cars at one time or another.

Be sure to post what you find so that the rest of us can learn something new.

Good Luck,

Jim Henderson

 

Sorry, I usually put the truck info at the bottom. It is a '95 F-150 4x4 5.0L SC SB.

Some added information, I flushed out the cooling system and put new coolant in when I changed the thermostat.

Thanks.