Overheating

[1965-Mustang]

Hello. I am having an overheating problem with my 65 coupe and was looking for some advice. I just replaced the engine with a rebuilt 289 and was using all my old engine parts such as intake, carb and radiator. Well my carburetor which was a 4160 holley single feed was not working correctly (never had) so I replaced it with a new Speed Demon 575 cfm. Got it inspected at my local shop, he got the new carburetor on and running, and fixed a vacuum leak which drained my checking account of what I had. I am 17 and dont have much money left to bring it back there :/ . With all this done I had only driven it home which takes about 5 minutes. I did not notice it overheating while driving. Next day I had it running and idling in my driveway when it boiled over and shot coolant out the radiator. It also would not idle unless I was giving it gas until it warmed up a little. It would not like to move from idle either when slowly letting out the clutch it would only move when I kept it revving at about 1500 rpms. I read online that too lean idle mixture would do this, so I adjusted that a little with the four idle mixture screws on the carb. Now it lets me engage the clutch and move just fine, it also seems to be idling a little better, but im not sure as it was already warmed up. During the engine swap I kept the old radiator and painted it and kept my old 4 blade fan. The fan is real close to the radiator with the spacer so that seems ok. Im thinking now I'll probably need a new fan and a carburetor tuning by a professional. I was thinking either an electrical fan or more blades with a shroud. I want to drive it so bad but im afraid to. Is it my old crappy fan or radiator?
Sorry for the long post and thanks to anyone who reads this and replies .

 

[302 coupe]

Is the radiator clean on the inside? Is the thermostat installed correctly? Are their air bubbles/pockets in the system? What is the timing set at? What do the spark plugs look like? What is the idle speed?

 

[latamud]

If you painted the radiator too thick it can clog the fins. Your thermostat could be stuck closed, if that's the case replace it. If you have the head gaskets on backwards it could cause high temps. If the lower radiator hose pinches at higher rpms.

 

[84convertablegt]

u have to use a certain type of paint on a radiator, i cant remember what kind, but using a regular spray paint can totally block the heat exchange properties of it. also, u need to replace the thermostat with a 160 or 180' high flow model. get a hp thermostat, its well worth the extra few dollars. does it overheat at idle? that is common since the waterpump isnt moving as fast, besides 65-66 models are notorious for this, with such a small radiator. also, buy a 16lb. radiator cap instead of the standard 13lb. unit, this will raise the boil over temp and pressure. these few things worked well for me. u may also need a new 3 or 4 row radiator.

 

[1965-Mustang]

Wow, thanks for the replies. Sorry forgot to say I also replaced the t-stat and it idles around 700 rpms. I had flushed the cooling system and refilled after running so no pockets, also put in water wetter. The plugs looked fine, I checked them all. I did use regular spray paint though. Looks like I'll be looking into a new radiator then. . . Anything aluminum with a good price and cooling ability? I'll also look into the cap as i have a standard one.

 

[XXBULLETSXX]

I guess I'll chime in.
True, you need to paint a radiator with special paint so as not to reduce the heat transfer of the radiator.
If you don't have a shroud..YOU SHOULD. It makes your fan much more effective and keeps it from sucking air from the sides.
The electric fans are a good way to go and they don't require a shroud. Down side is that they suck I lot of electricity and your alternator will have to keep up. I personally have taken that route and with a 60 amp alt. it loses ground while idling.
Lastley, how may cores does your radiator have? The way to check is to open the cap and look down into that radiator and you should see some openings/holes where coolant runs down from the top into seperate cores. Now if you have less than three, you need more and if you're replacing your radiator then get a four core. Those are not much more and are very hard to overheat. You'll thank yourself for spending the extra couple bucks.
Oh and replace your thermastat for the heck of it with a 160 degree and make sure your coolant mixture is at 50-50. Remember it's the water that transfers the heat and the antifreeze that keeps it from boiling.
Good luck and let us know how you do!

 

[iskwezm]

is the t-stat facing the right way?

 

[1965-Mustang]

Sorry for bringing this back up, but I am still having a little trouble.
I had replaced the t-stat with a 180, facing the right way yes. My new temp gauge from auto-zone has the sensor in the heater line so everytime the t-stat opens I can see the temp go down. So I sit in the car watching it. . .It stays low at around 180. It will go up a lil above 180 then go back down like it should, so I know it opening. But after about 3 times it just slowly rises until it gets to hot and I shut it off. Then steam comes from radiator. What would be the cause? Radiator not cooling, water pump? I know the water pump gasket to block is not so great but there is no leaks from it, the cap is my old 13 lb one. Is there not enough pressure, no cooling? Im at a loss now. . . .
Thanks for any help!

 

[grego37]

If your cap isnt holding pressure, it could be the problem. your system needs to build pressure for it to work. Replace it with a new one, the higher lbs the better, as long as your radiator will hold, you should be able to use a 16lbs without any problems..

Pressure test your cooling system and cap with a cooling system tester.

 

[rufusbooth]

four Words:

Get a fan Shroud! It will make a huge difference.


Actually, There is one thing that you have not mentioned that will tell you where your problem is. How does the car act temperature wise when you are at speed (45 MPH+) like on the freeway? If you stay cool at speed and run hot when in stop and go or idling it is a VERY good sign that you have inadequate airflow through the radiator. If that is the case, see my comment above ;-)

The fan shroud will increase the effectiveness of your fan at low speeds like idle.
Cheers,
Rufus

 

[mustangdave]

Agreed, FAN SHROUD. Also check your timing to make sure its not too far advanced, but most likely FAN SHROUD.

 

[84convertablegt]

also, if it just gets hot at idling, its either like mentioned above, a lack of air or maybe just that the waterpump isnt pumping enough water at low rpm's which is common on these cars. try reving the engine a little and see if it starts cooling down. if it does, its a water pump issue, not a radiator issue.

 

[65fsbkhipo]

Sorry for bringing this back up, but I am still having a little trouble.
I had replaced the t-stat with a 180, facing the right way yes. My new temp gauge from auto-zone has the sensor in the heater line so everytime the t-stat opens I can see the temp go down. So I sit in the car watching it. . .It stays low at around 180. It will go up a lil above 180 then go back down like it should, so I know it opening. But after about 3 times it just slowly rises until it gets to hot and I shut it off. Then steam comes from radiator. What would be the cause? Radiator not cooling, water pump? I know the water pump gasket to block is not so great but there is no leaks from it, the cap is my old 13 lb one. Is there not enough pressure, no cooling? Im at a loss now. . . .
Thanks for any help!

Plain and simple. Since the rebuild of the engine and all the checks you made seem correct, and nothing else is staring you in the face by now, even after all the help you have received...its the radiator. Not to say that there is anything wrong with it, but it is not cooling the rebuild as it should. 64-66 Mustangs are nototious for overheats on bored out engines. Reason beimg, is the radiator was not designed properly. IF YOU ARE USING YOUR ORIGINAL RADIATOR AND IT HAS THE INLET AND THE OUTLET HOSES ON THE SAME SIDE OF THE RADIATOR, that is your problem. The radiator is not giving you enough crossfloow of the water through the radiator. The water is running down only one side of the radiator and being sucked into the water pump from the bottom hose into an already hot engine. A four core radiator nor an eight core is not the solution, the fix is a cross flow radiator. The original radiator were just enough to cool a standard bore engine, nothing more. Mount a cross flow radiator and get a close placement of the fan...your problems will cease.