I had to remove the intake manifold to drill out a broket thermostat bolt a while back and ever since putting it back on the road, the temperature gauge has acted funny.

Before, the gauge would warm up and the needle would point straight up - between the R and M in the word NORMAL that is printed in the normal range.

Now, after it warms up it almost never goes below the M and swings between the M and A. I know this is a hard to visualize, but basically the gauge indicates the engine is running a little warmer and it vaires where as before it was constant.

Any ideas what would cause this?

The engine runs fine and does not show any signs of overheating - just want to make sure this isn't an indication of something to worry about.

 

Mine does the exact same thing, has done it as long as Ive driven the thing. The oil pressure guage also fluctuates now and then too. I dont think Ford guages from these years are the most accurate out there.

But what would cause a sudden change like this? Well if there are any air pockets in the line or what not, that would create a sudden change in the temp reading as that pocket passes the sensor.

As long as its in the normal range I wouldnt worry about it too much. But mine usually runs in a different range all together, my needle stays in the r and the o section towards the cooler side of the guage and every now and then it peaks to straight up and once in a GREAT while it goes a bit above that, but that is very rare.

 

I had a similar problem and it was traced to a short in the wire coming from the sensor back to the wiring harness. Seem the wire had insulation that had been skinned off and when the engine compartment warmed up or the wire jiggled it would send bad signals back to the guage, I replace the wiring and the temp guage now stays steady. I also think the guages are not as good as mechanicals because I have installed a mechanical oil and temp guage and the electric guages hardly move when compared to the mechanical ones after you get the engine up to operating temp.

 

Good to hear I'm not the only one seeing this. I thought about air pockets, but it has been over a month since I got it back on the road and it still happens.

There is a coolant temp sensor in the intake manifold - not sure if this is the one for the computer or the gauge or both - I think I'll squirt some contact cleaner on it to see if maybe it has a bad connection.

 

On the last truck I had there was a broken clip on the wire connector that hooked to the coolant sensor by the thermostat housing. I got a leak in the housing and when hot steam / water sauirted out it hit the connector and the needle would swing wildly back and forth from norm to hot and back. In replacing the connector I found there was again worn insulation further down the wire going back into the harness. I just cut out the bad and splice/soldered in some new wire and connector. No more swining needle.

 

The one for the Computer has two wires on it and the one for the gauge has one wire on it.

 

The gauge sensor is a little thing about the size of a dime on the drivers side lower intake, a single wire presses on a stud on the top of it. This sensor is not connected to the computer at all and only drives the temp gauge on the dash. The 2-wire sensor near the thermostst housing is connected to the computer and is not connected to the dash gauge in any way.

 

Ok,
I repaired the one with 2 wires so if it is going back to the computer.
I guess the computer takes the signal from the short and sends it to the guage?
and that makes the guage go up and down. Maybe?

 

no, the 2 wire one only tells the computer what the engine temp is for the management of the fuel injection system, it has nothing at all to do with the gauge in the dash. did you replace the thermostat with one of a different temp than the one that was in it?? check the single wire sending unit and make sure you have a good connection there. it could be coincidence and the sender just needs to be replaced.

 

Same temp I think it was 195 deg.
I think you have me confused with the guy with a probolem.
All I did was fix the 2 wires and connector and the problem went away. I dont know where the wires go. The ones I fixed were the oned from the sensor right by the thermostat housing. It had 2 wires/The clip had broken and there was insulation rubed away and gone.
I looked and found the one wire thing you referred to and it was fine. no missing insulation. Didnt even know there was another one. But thanks. Mine is working fine.
It was swinging back and forth before I replaced the connector and about 8 in. of wire.
It may have been a coinciidence like you said, all I know is the guage went back to working without sudden swinging.

 

rpatrick: Did you re-install the same thermostat or put in a new one? I was just wondering if you got a new one that has a higher heat range without you knowing it.

 

broncoboke, my response was a combination of answers for you and rpatrick, i just have a habit of responding to everything at once and not specifying to whom each responce is for. sorry for any confusion.

 

actually Its probably me.
I was also working on another thread about my question on those tiny holes on the
thermostat. I replaced it with one with the holes and fixed the conector at the same time. So I think I probably was answering the other question here. Oh well.
When you get as old as me. There is bound to be a short circuit somewhere.
Thanks anyway.

 

I used the old t-stat - But I definitely disconnected the 1-wire gauge connector to remove the manifold.

I'm gonna check the connector when it stops raining...