Hello~!
my 1998 F-150 4.6 triton has been a GRRREAT TRUCK! so far, except for minor maintenance stuff, never let me stranded ever!
My problem is that as soon as I click the ignition switch "on" with the engine not even running, the temperature gauge goes from cold to hot~!.
I replaced the temperature sender and the sensor but the problem continues!
Any idea on what may be causing this?? Any help will be greatly appreciated!
Thanks.

 

Possibly the thermostat is messed up. Does the motor actually overheat, or is it just the gauge? If the thermostat doesn't divert to the radiator once the motor warms up, it will continue to heat up and eventually overheat. If this is happening the gauge will rapidly rise to max.

Does the gauge instantly peg to max, or does it just rapidly rise there once the motor starts? If it just pegs there instantly, there could be a short somewhere in the gague's circuits, or the gauge could just be on the fritz. Head to a junkyard and grab a gauge panel off an old truck, and swipe it's temp gauge. They're all the same, just plug in and go.

 

in the temp sender wire look for a short to ground. sounds like that is the problem or else the gauge is shorting to ground internally

 

Guys, it don't work that simple anymore.
The gages are micro processor controlled.
Do the DASH testing to see what fault is displayed.
The first test sweeps all the gages.
Forth test returns all the gages to rest.
If the temp gage does not return, it's new insturment cluster time.
Somewhere in a recent thread is listed all the test info under HEC CODE testing.
If the sensor or it's circuit were faulty you should have a code to support that.
In addition, you never see the temp go beyond a certain point on the gage because it does not repond in direct relation to engine temp except from a cold start to that mid point.
The oil gage is not a gage at all but a meter type readout that is set to move to it's mid point when the oil sender 'switch' closes at about 6 psi. The engine oil pressure normally runs as high as 75 psi on a cold engine and as low as 25 at hot idle.
I know this is not well accepted but nearly all the gages are driven in the same way and do not reflect the true engine conditions. If you notice there are no measurement points on the gage diaplays that really mean anything.
The PCM does all the alerting with lamps, CEL and codes.
The reasons why this was done can be debated but it does no good to do so.

 

I am having this same problem. I can be running and then the temp gage will peg out. I can turn the truck off and them crank it back up and it will run a while and do it again. I have all new sensor's. Any idea's. It's a 1998 F150 4X4 4.6 .With a new engine.

 

Actually it is that simple on the truck. the 97-99 had two temperature sending units in the intake manifold. one went to the PCM, and one went to the "dummy gauge" on the cluster.


If the truck is actually over heating, then i would look at the radiator to see if its clogged up, and check the clutch on the fan to make sure it is engaging and holding like it should.

 

I don't see but two on top and they have been replaced and the wire's have been checked. The temp gage still goe's from cold to hot on start up some time's and some time's it don't but here in the last few day's it has been doing it bad and when it doe's it starts to run bad.The engine is not running hott. All is new!But the wireing.

 

X2 X2 to PatMan03 as these years had the simple analog gauges.

should be a simple short or faulty componant (temp sending, thermo or gauge)

 

Must be the gauge ? but I don't think so. Is there a way to check for a short ? Can not find any thing on it in the book.

 

to check for a short to ground or power, with the truck off, Ohm the wires to ground and to power. If you have low resistance to ground or power you know which wire the problem is

 

go away spammer

 

Thanks, I will do a check this morning. I just can't figure this one out.

 

Still no luck. It is starting to peg the gauge out more and more. I have to stop the truck and re-start it to get the temp gauge to re-set. HELP !!! Then it mite run for an hour before it happen's again...

 

Who you calling a spammer ?

 

Forget it. I was thinking of something else....