Recently purchased a 68 289 and the car seems to have an overheating problem. Radiator seems fine, was missing thermostat and have repalced, have replaced Rad cap and some kinked hoses. The heater was bypassed I'm assuming due to heater core problem, but I haven't gotten to that yet. It has A/C which is not working as well. Thought I had the problem solved when I replaced the kinked bypass hose, ran it for a few hours but didn't take it for a ride and it was fine. Yesterday took it out. Ran it for about an hour and a half stopping and starting while doing errands, it never went pass the mid-point. Then I decided to take it out on the highway and within two short exits the guage was going through the roof. Pulled it over before it started to smoke, but as soon as I shut it down the steam and antifreeze was spewing out of the overflow hose. Believe it or not the radiator cooled down in under an hour just when AAA was arriving. Rather than have it flatbedded I topped off the antifreeze(turned out I didn't loose too much) and proceeded to my friends garage about 20 minutes away, just made it before another boil over(that was by the streets and not highway). I will note I haven't hooked up the air cleaner yet which wasn't attached when I got it(not sure this would account for anything, its a closed system). Starting to think head gasket issue, the prior owner did his own rebuild, but wanted to get some opinions before the bucks spent. Thanks for the help!

MustangBonnie
68 Mustang Coupe
72 MGB

 

if it gets hotter while driving on the highway even with strong air flow coming thru the rad, then most likely its an internal problem in the engine, I would think head or head gasket as you mentioned.

However, you need to make sure your fan is close to the radiator, about 1" is good, and you should have a good fan shroud, no cracks. The fact that the previous owner bypassed stuff and removed the thermo, they must have already got the engine too hot and may have done damage to the heads.

Timing that is too far advanced can also cause heating problems, but I still think its in the heads.

 

You mention that the radiator "seems" fine. What do you mean? How did it flow with the stat out, could you see the coolant swirling with the cap off? If you had a bad head gasket, you would almost certainly have coolant in the oil. Are there any signs of coolant in your oil or a creamy substance around the oil fill cap? Does it run on all 8? If it runs good and doesn't have coolant in the oil I doubt its a head gasket. I'd get the radiator checked out FIRST. A good shop should be able to check it for flow. A partially clogged radiator will have enough capacity for short low speed runs but not enough to cool when the motor is working hard at high speeds.

 

i had the same probs. before and it turned out to be my head gasket. but 69fe is right about how to check it. look at that radiator fluid milkley stuff is no good. you can also smell it, you can smell...how do i describe it...like a combustion type smell if you blew a head gasket. Also i would replace to an elec. fan that stays on all the time IMO they work alot better. Another thing is you can switch to maybe a 3 or 4 core radiator allumium or brass. much better cooling that a steal 2 core.

 

I had the same problem with a 68, 289 coupe a number of years ago. At around town speeds it was fine but at freeway speeds it was "How far to the next watering hole".
It turned out the radiator was pluged with years of crap, and looking through the cap didn't provide for a good look inside the core. Having the radiator professionaly cleaned out did the trick.
If it was a head gasket, it would be pressurising the cooling system and overheating at all times.

Best of luck[sm=smiley20.gif]

 

Could it be a bad thermostat? I know you just put a new one in but it could still be bad or up side down.

 

The first thing I would do is take it to a rad shop and have them pressure test it. That will tell you right away if you have any leaks. Pump it up to 15 pounds. Do the check with the engine shut off first. If none can be spotted, listen at the carb and exhaust for any hissing noises. If you can't hear anything, relieve the pressure, start the engine and watch the gauge on the tester. If the needle starts climbing in steps,(jerky like) you have a leaky head gasket. Meaning your pistons are pumping air into your cooling system. Hence, the fast overheating. If it is pumping air into the system, it does not mean you are getting water into your oil. If you pump the pressure up to 15 pounds and it stays there, you have problems elsewhere. If you let the pressure build and it goes up to around 15 and stays there, again, you have problems elsewhere. I'd look at the rad as the culpret. Many times the rad may flow good with a flow test (rad out) but the tubes will be rust coated. If the rad shop tries to rod the rad out and a bunch of rust starts boiling out, best bet is a new rad. I bought a new Modine for my Z car for 145.00 with a lifetime warrentee. Also, another often overlooked problem is a bad water pump. It may turn and not leak, and not even wobble, but the veins of the pump may be rusted. I can go on and on about the cooling system, but this should get you in the ballpark and probably cure your problem. NOTE: Never, never use straight anti freeze. Don't go more than a 50/50 mix. And, use distilled water, not tap water. Distilled water will not boil if you put a cup of it in a microwave. Make sure you use a good flushing agent when you change the rad or before you put new coolent in it. By using distilled water, your chances of it rusting again are slim. Hope this helps.

 

Well it looks like the radiator is the culprit. While there were no leaks and it heat evenly it does appear there were partial blockages. Just ordered a new one and going to save the original, might want to take the car to the next level since it's in amazing shape. This car still has the original undercoating that was put on and not a piece of metal has been replaced or needed to be replaced. I want to thank you all for your input, hope I can do the same some day!

MustangBonnie
68 Mustang Coupe
72 MGB

 

it needs a new rad!!!!!!.......go to a 3 row when buying a new one

 

Or a 4 row. If you go with a 3 row, you just put it in. A 4 row you have to move the fan back alittle. Both are better then the 2 row that can't keep my car cool. A 3 row can't do it. To many horses.