Overheating issues solved for $0 on long trip in 86GT.

[twistedwankel]

Driving home 1100 miles from where I bought this 86GT AOD Conv twice the temp gage spiked to full hot and so I immediately pulled off the road and shut it down. Everything seemed normal and I could even touch the radiator so it appeared to be an electrical glitch. I had all ready deduced not a head gasket issue the night before as radiator was still full of water when cold. Still couldn't rule out the AOD overheating yet.

Sure enough playing with all the AC controls and driving fast again up to 75mph I was finally able to reproduce the conditions that made it spike hot (noticed that the fuel gage read high too)...aha. I had flipped the fan to max and forgotten about it.

Turns out running the heater/ac fan on high is the culprit as it must draw too much current lowering the voltage and fooling those gages. Putting it back on low speed and no issues whatsoever for the remaining 400 miles home.

So there is the solution for probably alot of us driving in AC fan required areas running fans on high.

Hope this saves someone else a lot of grief or unnecessary fixing.

 

[RatStang]

It doesn't sound as if you've fixed the problem yet though. You're getting stray voltage through either faulty wiring or improper grounds.

 

[HISSIN50]

The gauges have a voltage regulator so low system voltage should not affect them.

Another vote for a bad gauge cluster ground.

 

[mustang863]

allmost the same problem fixed

i went and got a fox 5.0 well same problem happen i thought i could stop it over heating with the heater ac but when i got it home i found out the guy had the thermostat was in back words lucky me dident blow head gaskets

Driving home 1100 miles from where I bought this 86GT AOD Conv twice the temp gage spiked to full hot and so I immediately pulled off the road and shut it down. Everything seemed normal and I could even touch the radiator so it appeared to be an electrical glitch. I had all ready deduced not a head gasket issue the night before as radiator was still full of water when cold. Still couldn't rule out the AOD overheating yet.

Sure enough playing with all the AC controls and driving fast again up to 75mph I was finally able to reproduce the conditions that made it spike hot (noticed that the fuel gage read high too)...aha. I had flipped the fan to max and forgotten about it.

Turns out running the heater/ac fan on high is the culprit as it must draw too much current lowering the voltage and fooling those gages. Putting it back on low speed and no issues whatsoever for the remaining 400 miles home.

So there is the solution for probably alot of us driving in AC fan required areas running fans on high.

Hope this saves someone else a lot of grief or unnecessary fixing.

 

[MustangLX-5.0]

I have this problem on both of my cars. I get it worse when I've been idling for a while and the alt gets hot. I've pulled the gauge cluster on both cars, unplugged them and cleaned, looked for ground straps etc. Still haven't resolved it. Must be some hidden ground wire attached to the firewall behind the upper portion of the dashboard, because I can't find it and I have cleaned every other ground I can find.

 

[twistedwankel]

This post is helpful from foureyed site. Might fix issue?

That sounds like the dash ground is loose, or is otherwise not bonded well to the dash
hull. The blower motor grounds through the same point as the gauges. The fix for that
is also free.

The dash ground is on the top side of the steel support, just to the left of the glovebox
door hinge. It's a hex-head sheet-metal bolt with a ring terminal under it.

Usually the dash ground doesn't ever loosen, but all bets are off whenever a car stereo
installer has been under there. The grounding bolt may have been left loose, or worse,
overtightened.

I like to put a star washer between the terminal and steel support, just for good measure.

I would also check the bolts at both ends of the dash, that hold it to the body.
__________________
Cheers,
Jeff Cook

'79 Mont StaWag, 5.0, 58K original miles ... '81 Futura Coupe, 3.3, 62K original
miles ... '85 GT 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT AOD
Vert ... '65 coupe, 289 auto ... '67 coupe 6-cyl 4-speed ... '68 Vert 307 4-speed
(And a Blue 2003 Mercury Marauder)

 

[twistedwankel]

It doesn't sound as if you've fixed the problem yet though. You're getting stray voltage through either faulty wiring or improper grounds.

This is a "Ford problem" that just turning the radio up didn't fix. Usually stuff just falls off ending issue. I got home and Henry smiles from his tomb. Gotta love Henry.

 

[BlackGT89]

Yeah, that and probably the fact that nobody expected these cars to still be on the road after 20-30 years. Actually, I think they do pretty good all things considered.

 

[grainboy]

To the original poster, I believe the blower fan is drawing too many amps due to age or lack of lubrication. This is common for 80-90's fords. I melted the fan speed switch in my pickup from the same problem. A new blower motor is an easy repair.

 

[twistedwankel]

To the original poster, I believe the blower fan is drawing too many amps due to age or lack of lubrication. This is common for 80-90's fords. I melted the fan speed switch in my pickup from the same problem. A new blower motor is an easy repair.

I agree as after replacing the instrument cluster voltage resister (this week) which fixed all the other gages, cleaning and replacing the sending unit in the block which corrected the wrong readings on the temp gage - I still get about an 1/8" increase in the temp reading (up to straight up Normal) ONLY on the High Fan setting which is alot more amps than the other 3 speeds. My solution is to not run on the highest setting and everything is just fine.

Some day I will replace the fan motor when it quits