when i start my truck 95 , the temp gauge already is reading 1/2 on the scale... right on normal, even after the truck has been sitting for a week and i know the engine is stone cold. The the gauge slowly creeps up like it would normally and finally settles on the H. I replaced the sender in the block and nothing changed( the sender under the #6 intake runner... a real pain to get to!) it just started doing this not too long ago because the gauge worked fine when i bought the truck. Any ideas?


95 F-150
300 I6
5spd

 

It sounds more like a sticking thermostat problem . How old is the coolant & the thermostat ? Any coolant leaks ?

 

well, not sure! i just bought the truck about 2000mi ago. The temp guage worked when i bought it. Then i was leaving a park, started the engine and the needle was pegged out ( had been sitting for well over an hour) so i immediately turned off the truck, checked the hoses and they werent hot... under the hood wasnt hot either. SO i started it back up and let it idle for a few minutes. the gauge after a minute flicked down to pretty cool and then instantly shot back up to H and did this a few times before settleing down where is should be. THen the next day...it just started doing what it is now.

I thought about it maybe being the thermostat... but i checked the coolant myself right after i started it and the coolant was not hot. Then after sitting for a week... i started it and it was immediately reading 1/2 way on the guage as soon as i turned the key. I'm sure it has to be something electrical. I might replace the thermostat anyways though

 

Trace the wire from the sending unit & see if it isnt chafed or damaged .

 

well, i traced the sending wire, and didnt see any shorts in it. So i unplugged it and cleaned out the connections... still doing the same thing. So then just for the heck of it, i unpluged the sender, and started up the truck. Even with the sensor unplugged the temp guage was reading 1/2 on the gauge! only difference was it didnt move once the truck started to warm up. Something wrong with the gauge i'm guessing?

 

I recently found a problem with my own truck , Erractic oil psi gauge & instrument panel lights , I found the instrument panel fuse loose & partially melted , Start there & see what you find . It may be you have a problem with the printed circuit board , particularly the section that feeds the temp gauge , The Instrument Voltage Regulator may be causing the problem as well . Ive found some of the Ivr's not making good contact with the circuit board . The 3 little contact pins on the Ivr can get dirt & dust under them . Clean the area & carefully bend the pins just a little so they make better contact with the circuit board . Also make sure you check any engine bay ground wires , there are lots of them .

 

Had the same exact problem on my 94 F150. Turned out it was the sender in the block was bad. You didn't by chance wrap teflon tape around the threads of the new sender when you put it in, did you? If you did, it will cause a crappy ground and screw up the guage reading. One check you can do is to ground the lead that hooks to the sender. Once grounded the guage should move to hot.

 

well, yes i did wrap teflon tape around the sender so it wouldnt leak.

BUT the problem existed before i replaced the sender... and when i unplugged the wire from the sender, it was still reading half-way between hot and cold.... it should have been pegged out cold right? I
'll try grounding the wire to the block though see what reading that gives me

paul - i checked the fuses, and they are all good, at least the ones under the dash.. havent checked the ones under the hood. Is the voltage regulator behind the dash? I was suspecting that because all the other instruments work fine.

Keep the suggetions coming!

 

There's voltage regulators on the older trucks, like my '79. Not sure about the newer trucks. Teflon tape will prevent the ground from closing the loop. You shouldn't get any (maybe poor or erratic) reading with a poor ground. If you take a spare wire and jump the block to the inside of the sending unit wire elbow - the gage should peg out. My best guess is along Paul's lines, trace the wires real well to see if there's a piece that has bare wire touching a grounded surface. I'd try that before digging into the dash...but it is wierd that you get a half reading...any problems with your other gages?

 

ya i know, its real weird... i've seen them work... and seen them not work, never seen one work... but be 1/2 guage sweep off! All the other guages work fine, except the temp. I'll try to trace the wires back better, see if i find anything

 

All of the analogue guages in cars and trucks are DeArsival meters with different faces. The way they work is the needle is deflected by the amount of current passing through a coil in the meter. This coil causes a magnetic field that deflects the needle. Some of these meters float when they have the current removed, and some are spring loaded to force them to return "0". In the case of your temp meter, you can take the thermostat out, measure it's resistance (should be quite high, like several Kohms), then place it in a container of boiling water and it should change to probably 100 ohms or so, but very definately less. A good book should have the exact numbers. Doing this will eliminate the sender. (you can also do this in the truck by measuring the sender when it is cold, then warming up the truck and doing it again) Next measure the resistance of the wire that goes to the sender in reference to ground. With your key off this should be megohms. If the wire to ground is not megohms, remove the fuse and measure the wire again. If it is still not megohms, the wire is partially shorted to ground, look for corrosion near a connection. If it now reads in the megohms the problem is between the fuse and the meter (Temperature guage) Actually, from what you have discribed, I think the problem is probably in or near the meter, but this is a way to check it so you don't go changing things you don't need to. The quick check is to ground the wire to see if you have max deflection in one direction, and open the circuit (unplug the wire, with key on) to see if you have maximum deflection in the other. Herman