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Discussion Starter #1
Put on your thinking caps…

I have what I would call an overheating problem in my ’68 Cougar. It originally came with a 302, but about 27 years ago, I retrofitted a stock rebuilt ’71 351W, 2-barrel into it. It runs great and NEVER overheated until last summer. While running down the highways of America, I began to notice it was running hotter than usual, with or without the A/C on. It was a summery day and outside temps were a little high…but that never bothered the temp gauge before. The temp would continue to rise after a couple of hours of freeway and bumper-to-bumper traffic with no end in sight. Before last summer, engine temps, regardless of outside temps would hover around between 170° and 180° on the average. Now it closes in on 210°-215°. Nothing was leaking and belts were turning. Everything appears to be doing its job. Then, towards the end of summer, the temp gauge would climb even higher and faster with the A/C on. It doesn’t boil over; it just runs way higher than usual. It is now very uncomfortable to drive knowing it has the possibility of going nuclear. So now, on with the examination.

As I stated earlier, the car is STOCK with the exception of a 390, three-core radiator and headers. So here is the list of components I have recently changed in order to fix this problem.

  • New, three-core replacement radiator
  • High-flow thermostat
  • High-flow water pump
  • New radiator cap
  • Block coolant passages appeared to be free of rust deposits
  • All hoses and coolant/distilled water for a 50-/50 mix (old coolant look great with no corrosion or rust)
  • Temp rated (not centrifugal) fan clutch with stock, A/C rated, seven-blade fan
  • New A/C condenser (no bent fins, dead bugs or leaves)
  • Still retains fan shroud with edges sealed to radiator
  • Distributor advance is correct
  • Not running too lean
  • No loss of coolant
  • The oil is not cooked and is at the proper level
  • Head gaskets (old ones looked great)
  • Cylinder walls look good with no obvious signs of damage, in fact, they still retain the hone marks
  • The heads were not magnafluxed, but thoroughly wire wheeled and looked over VERY closely for damage
  • Engine now has about 80,000 miles since the rebuild and doesn’t leak a drop or burn oil
Now that everything is back together, it runs just as nice as before. However, it still has the same heating problem, but with a twist. After running at freeway speeds for half an hour or more, the temp begins to rise, same as before; more quickly if the A/C is on. Again, same as before. But what is different now, is that after running the freeway and I get into downtown traffic; the temp slowly drops and I mean slowly.

This car was super reliable until last summer and shows no glaring problem that can lead me to the “overheating” problem. Years ago, I had the same exact problem with a pickup. I could drive it with no temp problems, but get on the freeway for half an hour of more and the engine was just baking. I ended up replacing only the engine and the problem went completely away. Never figured out why it ran so hot only on the freeway.

Suggestions on where to go short of replacing the old Windsor??? Summer is here and I want to break-out of this COVID solace and drive…ANYWHERE!
 

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One thing I didn't see was the temp gage. They do go bad. I'd try a mechanical one and compare it with the one you been using. Also voltage reg in dash could be going bad. My 66 Stang has the old oil PSI gage and new voltage reg. But it always seems to read low when engine temp is reached. I put a mechanical on it to compare and ran it back so I could watch both while driving. 70 PSI at cold eng idle and 60 PSI down the road when eng is 185.
 

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in my application,545 blown fuel injected,my over heat problem was flow rate through the radiator, I had a northern 3 core, a frostbit 4 core, a be cool,8 different fans,3 different stats,3 different restrictors, a electric pump, checked head gasket,checked cylinders, checked the intake checked the true tdc, played with blower pulleys, my fuel injection temp sensor and my eqquis gauge was 6 degrees off,I installed a Delco sensor in the motor and it was within 2 degrees, I see you installed a new 3 core and a high flow stat what afco said to me was I am not letting the coolant sit in the radiator long enough, so I purchased yet another radiator but this was a "dual Pass" and he recommended a stock oe 180 stat and drill 2 1/8 holes 1 at 3 o'clock and 1 at 9 o'clock why that matters I don't know but I did and my engine dropped 35 degrees it was about 350.00 all said and done but I drive on a 95 degree day at 205 and at 80 out I am at 185 to 195 and I run a 871 on a 545 tubbed big tire car call afco and talk to the tech dept now my motor being all new stuff except for the block the older and much wiser tech guy there explained allot about the composition of the coolant erosion rates over time surface tension of coolants yadda yadda yadda one thing I learned the hard way is bigger isn't always better or faster when it come to cooling systems call afco I high recommend it
 

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in my application,545 blown fuel injected,my over heat problem was flow rate through the radiator, I had a northern 3 core, a frostbit 4 core, a be cool,8 different fans,3 different stats,3 different restrictors, a electric pump, checked head gasket,checked cylinders, checked the intake checked the true tdc, played with blower pulleys, my fuel injection temp sensor and my eqquis gauge was 6 degrees off,I installed a Delco sensor in the motor and it was within 2 degrees, I see you installed a new 3 core and a high flow stat what afco said to me was I am not letting the coolant sit in the radiator long enough, so I purchased yet another radiator but this was a "dual Pass" and he recommended a stock oe 180 stat and drill 2 1/8 holes 1 at 3 o'clock and 1 at 9 o'clock why that matters I don't know but I did and my engine dropped 35 degrees it was about 350.00 all said and done but I drive on a 95 degree day at 205 and at 80 out I am at 185 to 195 and I run a 871 on a 545 tubbed big tire car call afco and talk to the tech dept now my motor being all new stuff except for the block the older and much wiser tech guy there explained allot about the composition of the coolant erosion rates over time surface tension of coolants yadda yadda yadda one thing I learned the hard way is bigger isn't always better or faster when it come to cooling systems call afco I high recommend it
One of the reasons you rarely hear them tell you to take the therostate out. You have to much flow without it in.
 

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Discussion Starter #5
Thank you for the replies.

  • I did forget to add this info. I am not using the stock gauges. They were replaced with mechanical Autometer oil and water temp gauges. True, the mechanical temp gauge could go bad after 27 years. I’ll look into that.
  • I have removed the thermostat and it only slowed down the process. Super cold for a little longer, and then the rise to hot as described in the narrative. With the stock design thermostat, it seemed to overheat much quicker. With the high-flow thermostat, there was a significant reduction, but the problem is still there. The high-flow thermostat does have a 1/8” burp hole already drilled in it. Seeing this reduction, I replaced the aftermarket, stock replacement thermostat in my crew cab, tow vehicle which was kinda temp iffy on warm hauling days. Now, the temp needle stays in one place regardless of outside temps. So, coolant flow seems to be the truck and Cougar’s friend, so far.
 

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A few other things I've found. Get rid of the front license plate and holder, if they're still there, they block air flow. Do you have a seal on the hood that seals the air flowing over the rad instead of thru it?
 

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Generally if a vehicle overheats while driving at highway speeds it’s a water flow problem , since you’re getting 60 mph air blowing thru the rad

if it overheats sitting still or in stop and go traffic it’s an airflow problem

I’d try a direct drive fan without a clutch, as an test
It will be noisy but could help eliminate the fan
Perhaps the fan you’re using starts slipping too much or something

also try some water wetter or other additives by Redline .

and get a test tool or kit to make sure the combustion gasses are not leaking into the coolant from a head gasket or a tiny crack in a head or the block

also check and you will likely need to add some gaskets or home made seals around the radiator and support to make sure air can’t bypass the rad

I have an early Bronco and with those on slow trail rides in the woods you have to make sure the Air can’t recirculate under the hood

it takes the oath of least resistance and it’s easierfor the air to move back over the top between the support and hood and back thru the rad again Than push the air past the engine and out the bottom
Although this shouldn’t be an issue at highway speeds
But at highway speeds it’s easier for the air to go around the rad than thru it so make sure it can’t go around

and congrats for driving a classic car a lot
I installed Vintage Air in my 65 Falcon wagon and in my 76 K10 and will someday add it to my Bronco
And props for keeping it that long. I’ve had my 74 Bronco since 1995.
 

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I'm not sure the problen. If it is hot, not pukin into the over flow, it is not over heating. The vehicle can run too low (below 180) and too hi - boils out of the system (245+). There are abt a doz things U can wrk with to effect running temps. The big one - proper tune.
Here's the areas:
  • leaks in system; air in system
  • correct shroud (fan 1/2 in/1/2 out unless 'flex', that = 3/4 in)
  • coolant - mix, additives, age, cleanliness;
  • water pump - operation, condition; cavitation;
  • heater core - leaks, condition, it;s fan on/off;
  • block - water passages;
  • hoses - colapse, leaks;
  • thermostat - condition, temp rating;
  • radiator (sz, # rows, clean?, construction, materials - I like ol style copper)
  • radiator cap - pressure rating, condition, design;
  • fan (blades, design, clutch)
  • flush system last yr or 2?
Too cool (below 180*F) can B a problem too. So what is the actual problem? Is it ur concern the neddle rises too much? Or actual over heating? It sounds like everything is OK - takes a 1/2 hr to hit top, cools dwn in stop'n go. A problem woud B over heat at 7 - 10 min, over heat in stop'n go. The wind is keepin it cool (U go 80, 85 on freeway), fan is wrkin in traffic to cool...
For more fun graba hand held infared (big box auto prts store - free; or $8 at Harbor Freight), point it around, C 'top of radiator', follow H2O jacket to "back of motor", measure @ water neck/thermostat, middle of radiator, exit hose/bottom of radiator. Play, don;t worry yet, B a scientist, gather data...
 
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