'69 Overheating Problem


I have a 1969 351W 2bbl. The engine was rebuilt about 1,500 miles ago. At that time a 4 core 24 inch radiator was installed because I live in Maryland with temperatures that go anywhere from below freezing to well over 100 and thought the extra cooling was a good idea. I have a 7 blade fan with a new fan clutch and a fan shroud. The temp gauge currently reads anywhere from the lower 1/4 to the upper 3/4, but when it sat in traffic the gauge would slowly increase until it was almost at the redline but would cool down when it was driving. So I replaced the fan clutch. After replacing the fan clutch I went for a two mile drive and the car sat for one hour and when I went back it was vapor locked (I took the air cleaner off and pumped the throttle and could watch the steam come out from the gas as it vaporized. It was 40 degrees outside. All fluids are full and the thermostat is a 180 degree and has been replaced. At this point I am out of options as to what is causing it and would love for some input as to how to keep the car cooler because I am out of ideas and would like to drive this car in the summer as well but if it can’t handle 40 degree temps it definitely wont be able to handle 95 degrees. Any help is much appreciated! Thank you

Did you install a high flow thermostat or an auto parts one? In another post someone had posted how the auto parts store thermostats flow enough for a 4 banger but not enough for our good old cast iron v8s and I agree with him. Also, and I’m not trying to be condescending because I have made this mistake in a hurry before, is the thermostat facing the right direction? the pointy end towards the radiator? How tight are your belts? What is your timing set at? Timing that is too advanced will make your car run hotter. Fuel is a coolant so too much initial timing or too lean an idle mixture will only serve to make it run that much hotter. Have you bled your cooling system of air? Steam pockets will give erroneous temp readings from air being trapped around the probe from the sender. How much air are you getting through your radiator? Trying blowing some compressed air from the outside in to see how much flow you are getting across the fins. also are the rubber boots that help form a venturi around your radiator intact? This helps in channeling air around your radiator.

I don’t have them on mine unfortunately, but sitting at the average 7 minute red light in the middle of summer here in Georgia where hell bound spirits go “That place is hotter than home” I have had no overheating issues since I a) checked and found that someone (other than myself) installed the thermostat backwards and b) the fan clutch was almost completely freewheeling at an idle. This was happening with a brand new 24" radiator so I sort of feel your pain. You could also have some blocked or semi blocked coolant passages in the engine, heater core, or both which will help contribute to a less than efficient cooling system. For you sake I hope the heater core is ok as they are a p.i.t.a! Also make sure your fan is on facing the right direction. Not trying to talk down just trying to help you eliminate every variable I can from this armchair. Take your cap off and make sure that your water pump is pulling like it should be.

Start simple like waiting until the engine is cool and double checking that the t-stat is in the right direction. Also when you blow air through the radiator make sure then engine isn’t running. The engine fan blowing air back will give you a false positive as far as if the rad is flowing air. Even a house or squirrel cage fan on high should be able to push enough air through your radiator that you can feel if it’s flowing or not. If you use compressed air have someone do it at a far enough distance that you don’t fold over your cooling fins and have your hand in front to see if you feel airflow.

With that size radiator and that temp thermostat you shouldn’t be having those kinds of issues from the cooling system, or need any aids in getting it to an acceptable temp. Especially at 40 degrees.

Well that’s all I have. That’s where I would start if it were my car.

Thank you very much! I triple checked the fan position before installing it as well as the thermostat so both are in correctly. The thermostat is a high flow. The system was bled and I replaced the heater core this past summer and so far that hasn’t shown any issues, aside from the fact that it’s not really all that hot (heather wise - gets warm, but not hot like new cars - I wasn’t even remotely alive when these cars were new so I guess that might be typical for them??). I had the belts and timing set by the machine shop where I had the engine rebuilt. Off the top of my head I can’t recall, but I want to say it was close to 6 maybe. The car idles correctly at about 550-650 when in drive once it is warm. Also all of the rubber is still intact. I will try the air test of blowing air through the radiator, but I’m just really at a loss. I also just found the video posted by WCCC on the cooling system and at this point am coming to the point where I might just scrap the cooling system and drop back down to a 3 core and the big block fan because there really should be no reason the car is having these heating problems.

Head gaskets installed incorrectly? Yes, they can be installed backwards and if so the crossover passage at the front will be blocked.

Yes; they were checked when I took it back to the machine shop that rebuilt it to see if that was the problem

Having your heater core only give warm air is not right; it should be good and hot. To me, that indicates there is poor water flow through the system, matching a lot of your other symptoms. When your engine was rebuilt, did they hot-tank the engine block to clean out all of the oil and water passages?

That I do not know and I will call and ask tomorrow. The block and cylinder heads were magnafluxed. Is that the same thing? Do you have any suggestions on testing the water flow? Because the heater is definitely just warm and nowhere near hot and it is a correct replacement and I installed and put back everything correctly (took a while but it all went back).

I found the machine shops notes. The block and cylinder heads were cleaned and magnafluxed. I also just read the other thread on an overheating 302 and many of their symptoms are what I have too. Everything on the block is new: the water pump, the radiator is brand new, all the internal parts on the engine were replaced as well as the fuel pump. The only original parts to the engine are the block itself, the intake manifold, and rebuilt carb. Since the heater is running barely lukewarm (you have to put your hand almost on the vent itself to feel the heat and putting your hand about a foot away from the vent just blows air from the blower motor). Everything is new, but it may sound like there could be a clog somewhere if a warm heater is a symptom and its not hot (in addition to everything else). How would I clean the pathways where the coolant flows? I know about radiator coolant flushes and can do those, but how would I clean/ test the block for a clog somewhere? I’d prefer not to take it to a shop because I like doing things myself (and as a college student it saves some money), but if I have to then I guess that’s what must happen. Thank you for your help so far! I’d just really like to see it back out and driving and not have to worry about consistently watching the temp gauge when I drive it. Also, would it be a good idea to swap the radiator to a 3 core and/or the cooling fan to a bigger size or does my current set up with a 4 core and 7 blade fan work?

It isn’t. Magnafluxing is a process by which the block and heads are checked for cracks.

Some things I’ve had with overheating and cool heater.
Air or clog in the heater hoses or core - disconnect both heater hoses from engine and put garden hose into one and see the water flow coming out other.
Always open thermostat - plate pulled back and edge stuck on spring
Impeller loose (Hi Royce) in water pump (its pressed on) flipped backwards
New intake manifold gaskets that have punch outs for the front water passages - not punched out
Make sure you use the original temperature sensor or a Ford NOS. The repops (parts store) have the wrong resistance or are for idiot light, will show hotter then it is

Didn’t even think about the head gaskets being backwards, but that could DEFINITELY be a possibility given the recent rebuild. Especially if it ran at a normal temp before the rebuild. Only one way to tell and it’s not the funnest way. Amen on the parts store sender too. Had that problem as well on another car.

For your sake I hope that one of the other tests finds a fix that doesn’t require tearing the top end apart to correct.

Few more toughts that are really basic and you probably know, but sometimes simple things get forgotten:

  1. air pocket left in the cooling system if not bled properly while/after filling;
  2. heater control must be placed on “warm” during filling to obtain complete filling of heater core;
  3. fan must be positionned 2/3 ahead of shroud toward the engine and not close to rad deep in shroud.
    Good luck!