66 mustang 289 over heating

[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.
Jackie

[stangjr]

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

[dewjac]

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

[Soaring]

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. 

[Soaring]

Jackie,
You need to get back with us to tell us what you did to resolve the overheating problem.  Or at least thank us for trying to help you resolve your overheating problem. 

[Lissesred66]

For Soaring, dewjac, anyone with ideas: 

Sorry for the long version but the details might be helpful?  There is actually a question at the end of this.

Found this thread and noted the suggestions.  We bought a 66 convertible that had a brand new, crated engine installed, but had never been hooked up or even hand cranked.  Sat in our garage for several years till we recently had the money to get it restored and on the road. 

A friend suggested several of the same things you all spoke of here.  We have a 289 that apparently has an ever increasing overheating problem.  Especially since we're now into the hotter weather. 

After warming up it begins to run rough at slow speeds or during stop/go driving.  It doesn't boil over - but temp gage will spike right as the car dies.  Stalls and acts like it's vapor locked.  When it cools off restarts and we can get it home. 

Changed the thermastat putting in a 160 instead of the 180, fluid seems to be circulating OK - Driving at road speeds is fine - I suppose due to the air movement across the radiator. 

We have a shroud we'll be adding.  And considering changing out the current 4 blade fan to a 5 or 6 blade.  We have an over flow hose but not a tank.  We'll have to check out the bottom radiator hose to see if there's a vaccum problem and it's collapsing.  We read somewhere else that could be an issue? 

Our friend suggested the air pocket in the system problem.  We tried the fix he suggested by removing the rad cap, watching for movement (yes it appears to circulate) then the fluid bubbled up as if releasing a good sized bubble.  He told us if then the level suddenly dropped to  add more fluid to the proper level.  Which it did, and we did.  Alas it didn't work - in fact the car over heated even worse.  This time had to be towed home.  Our regular mechanic doesn't normally work on older cars like this & couldn't readily find the problem.  Said something was causing the valves/pistons to expand.  He felt the cooling system was OK.  I have to find out if he pressure tested it.  The guy who did the restoration (he's really only a body guy) is away but will come over next week to check this all out.

In the meantime we're going to try some of your suggestions.

My question is this - someone else (everyone at work is an expert all of sudden, lol) suggested that you need to have the front of the car raised up slightly in order to get all the trapped air out.  The angle helps the air escape? He says it makes it easier for a trapped bubble to move thru the engine block and finally out?  Any ideas in that theory?  Is it bunk?  We want to do this the correct way.  So any ideas are helpful.

Thanks in advance for your suggestions.

[Soaring]

Oddly enough, I was listening to a car show this morning on the radio, and the caller had an overheating problem.  The host of the show told the caller to raise the front of the car up then burp the system.  I don't understand the theory behind that, but hey, it can't hurt to try.  And also, go to Autozone and get a bottle of "Water Wetter" and add to the system. 

[Lissesred66]

Will give the Water Wetter a try - thanks.  We'll let you know how it works out.  Due to work schedules might be a week or two till we can try the burp method.

[66GTKFB]

There's one cause of overheating that everybody ignores - a pinhole from the water jacket into a cylinder. It doesn't happen very often, but it does happen. It took 35 years to for mine to become a problem. The location was discovered when I had the block bored 0.020 in over. Then the pinhole grew to a 1/16 inch chasm. Located in number 8 cylinder, this was the third one I encountered and all in number 8. This was the first one for a car I owned, the other two were engines I worked on years earlier. They don't call the 289 a thin wall block for nothing. Sleeving the cylinder worked, but I put in a different block in mine.
Jim

[Lissesred66]

Thanks for another heads up.  Another item to add to the list if other things don't check out.  Car refuses to start at all - have more experienced people comming this week to look it over with us.

Thanks for your suggestions everyone - will have to get back to you when we figure out the problem.  My husband is retiring next month and work schedule comes first for this last 30 days.  Hopefully it is something more readily fixable - but I have that bad feeling......