Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

67 Mustang overheating

I added P/S, Classic Air A/C, replaced radiator, radiator cap, water pump, thermostat, fan (electric now), intake manifold, carburetor. I have taken it to 3 mechanics and found no solution. I spent over $6000. The original water pump pulley did not fit, so I replaced it with a different one from another vehicle and added five washers to push it out. Engine was last rebuilt 1998, but only has been in use for about 5 years, has been sitting on and off. I am running out of money so I am on a budget. This is my daily driver. Hope you can help. Any information would be appreciated. Thank you.

You added AC to a vehicle that originally didn’t come with it. Did you upgrade to higher capacity radiator when installing the AC?


When does it overheat? Idling, slow speed, freeway speed, all the time? Be specific.

Is it losing any coolant that you don’t see on the ground? Is there white “smoke” coming out the exhaust? If so, it may have a blown head gasket, cracked head or cracked block.

Tester’s question is quite valid. Does it overheat when you’re not using the A/C?

Of course one of the mechanics you took it to should have caught either of those symptoms immediately.

Assuming the engine is OK, no head gasket issues. The OEM radiators in '67 Mustangs is small. I had a '67 Mustang that I bought new with a 289 2bbl carb, 3 speed stick. The car would overheat when stuck in summer traffic on a hot day. I had to rev the motor to increase the fan speed to pull enough air by the radiator and sometimes had to run the heater on full blast to cool the motor coolant, not fun on a hot day.

If you are running the OEM sized radiator, and you added AC you are going to have problems. The electric fan will help, but you need a bigger radiator. I added a coolant overflow tank to my '67 somewhere around 1970. That allowed me to run coolant with no air in the system which increased cooling efficiency and cured my problem. It also made the water pump last much longer.

If you don’t have a coolant overflow tank on your Mustang yet, get one from a junker and find a place to hang it in your engine bay. It will make a big difference. It is still likely you’ll need a bigger radiator since you added AC.

Under what conditions does the Mustang overheat? Extended idling or high speed? Is the fan pulling air in or blowing it out? Did the AC conversion reverse the rotation of the water pump? Are you certain that the thermostat is correct and correctly installed?

289 or 390? Others have mentioned the need for a radiator designed for air conditioning. They have almost TWICE the cooling capacity. Also, does the car have a coolant recovery system? This will make a BIG difference in cooling ability…Have you removed the stock cooling fan and shroud hoping the aftermarket electric fan would do the job? Is the thermostat installed correctly, the copper “pellet” towards the block?

I would double check the water pump. Some Fords (if I remember correctly) used different rotation water pumps, so if you have one meant to rotate clockwise and it’s being turned counter-clockwise or vice versa, you are going to have cooling problems. I also agree with the recommendations for a coolant recovery system if you don’t have one on this car, as well as a larger capacity radiator if you can upgrade from what you currently have. Also, if all you have is the electric fan, you may also consider adding a flex fan. They are cheap, move a heck of a lot of air, and don’t sap your performance (the blades “flatten” when the engine is revved, reducing parasitic power loss). Also, if you removed the fan shroud, it needs to be there for any mechanical type fan (water pump mounted) to work at all.

I was going to suggest the wrong water pump scenario but mark9207 beat me to it.

With the small blocks the V-belt and the serpentine engine water pumps will interchange but the rotation of the impeller is different. Stick a serpentine pump on an older V-belt engine or vice-versa and it will not work.

Most potential issues have been covered but also curious if the cobbled up pump pulley has same diameter as OEM?