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66 mustang 289 over heating

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Jackie Jameson:
Hi  I am new to this area and I am very disappointed that I can not repair my problem.
Initally I bought the car  anout 3 years ago.  Supposedly rebuilt ( you know the deal).  It ran a little warm and left deposits of anti freeze around the motor area. I looked all over and could not find the leak.  A mechanic friend said he found  to hot a thermostadt and replaced it.  It did  reduce the temp/leak in most occasions.  The radiator is new  (3 tier).  When you drive on the highway it gets hot and over fills the ovrflow resovoiar.  It does get hot also in stop and go traffic.
Should I buy a bigger radiator (it seems that this would give more fluid to overflow).  What about flushing/back flushing the block?
What about pulling the thermostadt?
Any help will be appreciated.

Hey i hear ya on this one my 66 overheated like i was driving the thing over an oven. A couple of things i did that seemed to help the most were - Aluminum intake, Electric fan (eliminate stock fan), Front racing valance (Big increase in air flow).   but one thing that i still want to try is cut the radiator support and stuff a 69 radiator in there with a high flow water pump. Ive seen it done and it doesnt look that difficult plus it looks kinda cool!

Hope this helps.
And good luck :-D

I've found a fan shroud, five-bladed fan, correct fan spacer (fan half way into the shroud), carefully bleeding the cooling system and keeping the coolant level about an inch below the filler neck eliminates most coolant loss problems. If you are leaking coolant, the coolant pressure (and temperature) don't rise to operating specs and cooling efficiency suffers. Find and fix the leak(s) - make sure the radiator cap is sealing properly (just a little corrosion on the filler neck seat can result in low coolant pressure and coolant boil-over, also make sure the water pump bolts aren't leaking on the backside - the bolts going into the aluminum front timing cover are awfully easy to strip), find a mechanic with a coolant pressure tester and verify the pressure can rise to somewhere near the radiator cap limit (13 lbs on my 289). Don't even think about removing the thermostat, it won't fix the overheating and you'll have a new set of problems. Good luck and don't give up!

barry taylor:
ON my 66 mustang 289 I replaced the t-stat and radiator cap and had the radiator cleaned by a radiator shop.
still over heated >:(
new radiator cap - still overheated  ::)
correct raditator (2 time)  :(  and drilling three 1/4 inch holes around the body of the t-stat corrected problem ???

I also had the same problem with a Chevy 396 BB ended up doing the same thing drilling 3 -1/4 inch holes around the body of the t-stat to correct the problem :)

I agree with Dewjac.  I put on a 5 blade fan, a shroud, and overflow tank, a 4 row radiator and a 180 degree thermostat.  I put in a bottle of wetter water, and filled the system with 50/50 anit-freeze/water mixture, bled the system, and now my heat gauge never gets above 1/3.  I didn't drill any holes in my thermostat, but Barry has a point.  He's not the only one I have heard that from.  You have air trapped in the system which causes pockets of no water in the block.  The best way is to bleed the system, and the overflow tank will accomplish that feat in the first two times you get the temp up to operating temp.  Or, you can take off the cap and let the engine run until the thermostat opens and the water pump pumps the water and air to the top of the radiator where the air escapes. 


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