My temperature guage used to rise from cold to mid range and fall down to above cold then rise to mid range and stay there.
Now it rises to cold and stays there. I do have heat (although not hot) but the guage does not go above the first mark which is labeled "C".
My question is this: Is the guage screwed up, or is the thermostat stuck in the open position?

 

back in the dark days of '88 that used to mean the thermo was having problems, but since now-a-days the truck is so much smarter than me I dunno anymore. Code read it to see what the temp of the coolant really is.

 

I agree, it sounds like the thermostat is acting out.

When the engine has been run enough to have warmed up, with the engne at idle, raise the hood & feel the top radiator hose, it should be hot & uncomfortable to hold, if it's just warm, then the thermostat is likely stuck open.

If your in doubt about the temp, hook up a scantool that'll read PID's & have it give a readout on the computers engine temp sender, it's a seperate sender from the one that operates the temp gauge.

If the engine isn't warming up fully, you may be having driveability problems & poor mpg, as the engine will remain in open loop operation & running a richer air/fuel ratio, so the computer should be unhappy with that & set a trouble code & maybe tun on the CEL.

If you find the thermostat is faulty, be sure to disconnect the battery B- cable while your replacing the thermostat, to erase the computers memory, so it can begin to build new fuel trim tables & relearn it's cold & warm idle strategy with the new thermostat operating the engine at the correct temp.

If you have an auto tranny, you can help it relearn some things quicker.

With the vehicles front end raised & the rear wheels blocked on the cold restart, turn off all electrical loads, start the engine, let it idle down some, then slowly shift into ALL gears, including "R", such that you feel each gear engage, ending in "P" or "N".

Without touching or turning anything on, let it fully warm up, then shift into All gears again.

This lets the computer relearn it's cold & warm idle strategy, while the engine is circulating the refilled coolant, to burp the cooling system of air.

The remaining things the computer needs to relearn it can likely do while your driving in the city, or on the road.

I've never had to if doing the above, but If you still have some driveability problems, then do a search for & go through Fords lengthly computer relearn drive cycle.

Also, on the thermostat replacement & on the coolant refill, use a Motorcraft, or like thermostat, that has the air bleed valve feature.

On the coolant refill, as noted above, do it with the rear wheels blocked & with the front end raised on ramps, stands, or facing up hill, so that the trapped air wants to migrate to the radiator.

Leaving the vehicle raised when restarting after the coolant refill will allow the thermostat air bleed valve to pass air trapped in the heater core & engine block, on to the radiator, where the radiator cap can burp it out to the recovery tank, on engine cool down.

So leave the vehicles front end raised through at least one warm up & cool down cycle after the coolant system refill & while it's up, doing the cold & warm idle relearn cycle will kill two birds with one stone!!!! lol

A whole bunch of thoughts for pondering, let us know what you find & how it goes.

 

The heater hoses don't seem that hot, and the top radiator hose is warm to the touch but not hot................so I'll change the thermostat and see if that makes the guage go to the middle of the range.

Thanks for the input!

Tom

 

Replaced the thermostat today, and no change with the guage. So went to buy a new sending unit. There are 2 sending temp guages on housing, the one nearest the radiator is the temp sensor to the guage. Replaced it, and WALLA!, the guage on the dash went up to medium. The bolts to the thermostat housing were HARD to get out and put in.............O well, we like working on rangers, don't we!

Tom

 

Good find fix & feedback on your temp problems.

Kinda sounds like you may have had more than one problem????

When the engine is fully warmed up, Is the top radiator hose now hot, or at least more so than when you felt it, before replacing the thermostat & is the in cabin heater air temp now hot, or at least more so than before the thermostat replacement????

The single wire temp sensor is the one for the in dash temp gauge.

 

Yes, radiator hose is a little hotter, and the heat is a little warmer. Never did have "hot" heat in cab, Ford's blend door design is the pits. Oh well at least the guage is working properly and I'm not fixing anything else!