I just recieved a 86 ta with a carbureted 305, with 150k miles. It has been awakened from a 5 yr slumber and it is overheating. According to the previous owner it was running hot when they parked it & couldn't find out why. The situation: full of coolant, and the thermastat works but the temp. gauge doesn't register, and the electric fan doesn't cut on. The coolant temp. sensor has been replaced. I jumped out the fan and it works, also when starting the car the temp gauge sweeps to the high side then back down once the car starts. The coolant temp sensor wires have a ground, and 4.6 volts on the other with the ignition on, and no trouble codes. Could it be the output from the ecm is not working?

 

If the temp. gauge does not register how do you know it is overheating? Is the overflow tank overflowing?

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Big 454 72 Chevy Nova
383 86 Camaro Z28
10.5:1compression 186 casting Heads,234dur.488lift exh&int,Edelbrock performer intake, Holley750 vac.sec 400 crank,flat top pistons,edelbrock valve springs and lifters,tranny shift kit,2500 stall converter. Will install 3.73's later on and might go with a more aggresive cam.As of 4/01 added Hooker Headers,2.5inchpipes with 40 s. Flowmasters.Ignition upgrade include: MSD Coil and MSD module.

 

yes the coolant jug is boiling over. But there still is not temp registering

 

To fix the boiling over problem, try a new radiator cap. Boiling over does not necessarily mean overheating.

Which coolant temp sensor was replaced? There are 3 temp sending things on that car. One in the left head works the gauge; one in the right head is the temp switch for the fan; and the one in the water outlet is for the ECM. These 3 functions are totally independent, not interconnected in any way. So, put a new rad cap on it, and let it sit and idle and see if the fan cuts on and the gauge comes up. The fan turn-on temp is about 230°, so if the cap didn't hold pressure, it would definitely boil over even though the temp is normal, and apparently above the boiling point.

A mix of water and AF boils at a higher temp than pure water. Pressure raises the boiling point also. In a properly working cooling system, with 75/25 water/AF and a 15 psi rad cap, the boiling point is well above 250°.

Remember:
High temp (above 212°) does not necessarily equal overheating.
Boiling over does not equal overheating.

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"So many Mustangs, so little time..."
ICON Motorsports

 

try the fan relay switch..that should cut the fans on...does it overheat while driving or sitting still?...if driving then see if you have the little plastic part just infront of the radiator...Just sitting it will run hot yes but should not overheat. I would take the rad cap off and see if the coolant is flowing...If not then water pump...I would go ahead and put in a 180 thermo anyway. Hope some of his helps...