The ECT Sender should have a Red/white and a black/white wire attached

The Red wire runs to the temp gauge
The Black wire is the Ground

Remove the connector from the sender
Use a Volt/ohm meter set to OHMs
Ground one meters probe and put the other on black wires connection, should be 0 ohms
Move wiring harness around to see if ohms change, they shouldn't

Now do the same on the Red wire but switch meter to DC Volts
Ground meter probe and hook other to Red wire
Turn on the key, should see 6 to 12volts
Move harness around again, see if volts change, shouldn't

If ohms change then try to localize what wires moving causes it, check body grounds at firewall and any connector with Black/white wire, unplug it and look inside for corrosion

Same if volts change

If all is well then you will need to pull out the instrument cluster and check the red/white wire on the back


Actual temp changes so gauge is correct
If temp gauge goes up while stopped then goes down again while driving, most likely cause is the fan clutch is not locking when it warms up
Before starting cold engine, open hood and spin the fan, it should not spin, should be hard to turn, it is locked
Start up the engine, let it run for a 30 seconds or so and shut it off
Check fan again, should spin easily, it is now unlocked
As radiator warms up fan clutch should start to lock fan again
After a 30+ minute drive check fan again, should be just like when it was stone cold, locked

If fan spins easily at any temp then replace fan clutch

 

 

That could be two things
Electric/alternator voltage is dropping to low at idle, causing gauge to drop, but if you have a volt gauge it should go down as well

Thermostat is not closing all the way

Start cold engine and feel upper rad hose, should be cold of course
Leave engine idling and wait 2 minutes, feel upper hose again, should still be stone cold like it was before
Feel heater hoses they should be warming up, but NOT upper rad hose
If upper rad hose is warming up with the engine then thermostat is not closed all the way as it should be

Water pump issue would usually do opposite, hotter at idle cooler at higher RPMs

The heater temp should drop as the gauge does, at idle, does that happen?

 

 

The Lima engines, which is what you have, ran cooler than most engines, people in northern climates often put a piece of cardboard in front of radiator during the winter to keep engine bay and heater HOT, lol.

A trick I learned a long time ago was to swap heater hoses at the firewall, to reverse the flow thru the heater core, this makes then last longer, do it every 1 or 2 years.

The temp gauge going up when driving slow or stopped was the reason I thought fan clutch was the issue, not overheating, just the fact it goes up when air flow thru the radiator goes down
When you are moving the air flow is better than any fan can provide, but when going slow or stopped the fan must provide the air movement, if it's not then temp will go up a bit


Vent controls are operated by Vacuum
Defrost is the default, no or low Vacuum setting
If vents work when you are idling(high engine vacuum) but start to go to Defrost when driving, then vacuum issue is the problem, usually in the engine bay, a hose is cracked and leaking

 

 

96 ranger 3.0, temp gauge goes from normal slowly up almost hot then slowly back to normal then few mins later back up and down repeat ,I already put a thermostat in it.any ideals?

 

Welcome to the forum

You should start your own thread, unless you are commenting on original posters problem

If gauge goes up when driving slowly or stopped and then goes down when moving faster your Fan Clutch is most likely problem

If gauge goes up and down randomly then heater bypass or heater core is the most likely problem

 

Yea it's goes from normal to hot and back like that, randomly rather ur moving or not

 

Then most likely the a heater hose or heater core issue

The heater hoses are the By Pass for the water pump, i.e. before thermostat opens coolant needs to be circulated and the heater hoses function as a by pass to keep flow the same whether thermostat is open or closed
If there is a partial blockage in the hoses or core then circulation slows down until pressure is relieved then it comes back, this back and forth causes the heat up and cool down you are seeing

Some Rangers just have the two heater hoses, no valves, just straight hoses from water pump and intake to the firewall and heater core, if thats what you have then heater core is the problem, it clogged up, replace it.

On some there is a by-pass valve, 4 heater hoses connect to this valve.
This valve cuts coolant flow thru the heater core, usually only in MAX AC setting, so not a TEMP setting valve
So with engine running select MAX AC on dash and see if this Vacuum valve activates(moves), to bypass heater core, if so then go for a drive and see if temp issue is solved or not
If no up and down gauge then core is the issue
If gauge still goes up and down OR vacuum valve doesn't move then by-pass valve would be the problem, it's valve inside may have come loose and is blocking flow

 

Went out started it up,turned on max ac and left max ac on and went for a drive got bout a mile and temp hand sky rocketed higher that usually ,turned off max ac and it went back down to normal ,and jus does same ole thing
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Started it up,turned on max ac,let it run then went for a drive with Max ac still on ,the temp went even higher,turned max ac off and went back down to normal.

 

I would say the by-pass valve is the issue then

You don't need to drain all the coolant just enough to lower it below the level of the by-pass valve and heater hoses
Then remove the hoses from the valve, MARK them and take a picture, you will NOT remember and then will second guess yourself to death, lol

Once valve is out look inside and move the vacuum arm to open and close the valve inside and see what the problem might be