Stangfriik

Ok here is what's going on.

When a/c is off, temp gauge runs anywhere from the 2nd line above middle to 3rd.

A/C on makes it go to right below the redline

Even turning on other electrical options such as headlights increases the temp reading.

Maybe I have just never noticed it but I don't think it has always happened to the extent that it's happening now

I have filled the radiator and reservoir with fluid to no avail.

What other things should I look at?

Air filter? Thermostat maybe?

svopaul

The fact that it increases the same when you turn on electrical items tells me that you more than likely have an electrical problem. Could be a faulty voltage regulator on the gauge cluster or a ground problem somewhere.

I had a problem on my SVO years ago that all of the sudden the temp gauge was on meltdown but the gas guage and oil pressure also jumped up and the problem there was the cluster voltage regulator. Check and see if your other gauges increase their readings too.

If you want to rule out your actual temperature then a Raytech Pyrometer would be of great help if you can find someone who has one. Basically an infrared temp gauge that can tell you exactly what temp your radiator, hoses and engine block are by pointing and pulling the trigger. If you know anyone into road racing then if they are serious about it they will own one. I have one and it's invaluable for both road racing(tire temps) and in the shop.

Stangfriik

I checked today and when I turn my lights on, every gauge except the fuel gauge moves. Battery, oil pressure, and temp gauges all move.

So I'm looking at replacing the cluster voltage regulator? How much does it cost and what does the replacement involve?

Thanks

SVT Muscle

Check the ground screw located on the fender between the coil and the battery(closer to battery). Even if it feels tight, take it off, clean it up and re-tighten it. The same thing was happening to one of my fox bodies and that fixed it. On mine, every gauge was going all the way up except fuel and it would only do it when the lights were on

*I think that's the ground for the headlights*....

svopaul

That is also a good suggestion.

On the '86 there is a small silver box on the back of the instrument cluster which is the voltage regulator....however I believe the system may have been changed in '87 and it may not be the same type of design since they changed the gauge type. It definitely sounds like a potential ground issue.

SVT Muscle

Any updates??

Let us know

Stangfriik

Sorry work and school is taking up my life.

After hearing the suggestion from you regarding the ground wire, I noticed that the housing was actually melted and corroded in one place where it had been previous reconnected. I cut it and reconnected using a new connector and everything is fine. All gauges are back to the middle.

Thanks for the advice

Daysleepin

This maybe the thread for me.
I recently acquired an 89 5.0 and when ever I turned the key to the on position the gas gauge goes to super full (regardless of how much is in tank)
and the water temp straight down to the super minus position ( regardless of reality)

The oil gauge and amper gauge seem to work fine with little effect with turning on headlights and such. On one ocassion I did come to a complete (100% no forward motion) stop and noticed I was doing 40 MPH.
I also noticed the speedo was a little loose so felt there maybe a connection problem at the speedo cluster. I changed both gauges to no avail.

I also took the advice here and used 100 grit sandpaper to clean the ground close to the battery. Al tho it did not work for me I may need to try some of those skin cutting star washers tomorrow.
Wish me luck......