Just finished the restoration on my 1969 Cougar XR7 351 Windsor with A/C. Anyway took the radiator to a local radiator shop its the 24” (original fomoco radiator) to have it tested before I put it in the car. New Thermostat new fan concentric but when i get on the highway it runs hot at around 265 Degrees the pump is working fine and i did a leak test to make sure it was a closed system. The only thing I can think of is that the fins are blocked on the inside of the radiator. What are your thoughts? I have read that you can have the radiator boiled in a chemical but no-one in Chicago does that so the tubes need to be replaced. Is there anyone you know that does this?
Not a expert in the slightest. What thermostat do you have on it??? Im sure a slew of questions are to follow. So take heed in EVERYTHING you read here. Their knowledge is second to none.
Need to get some more information from you or to clarify what you noted in your original post.
24” wide OEM radiator
New thermostat (what temp rating? Did you verify thermostat is opening at that temp?)
New Concentric fan (I assume this is a mechanical fan not electric. Is that correct? Is this a thermal clutch fan or direct driven? What is the blade count? If electric fan/s how many and cfm rating plus are they wired and controlled correctly and does your alternator have the output to run them at full speed?)
Pump Is working fine (how did you verify this?)
What coolant or fluid is in the radiator? (Water, coolant and ratio?)
What condition are the hoses?
Does the lower hose have the internal spring?
Is your radiator cap new? What is the pressure rating?
Do you have a recirculation tank?
How are you measuring the water temperature you noted above?
At that 265f temp was the system boiling over?
Does that temp only happen while driving? Does it happen while running and parked?
Do you have a radiator shroud around the fan/s? What is the position of the fan/s within the shroud?
Think of the cooling system in terms of flow-both air flow and water/coolant flow-as you need both to exchange heat from combustion to the water/coolant and then from the water/coolant to the air. If you are only overheating when driving, that is typically a water flow issue as air is being forced thru the radiator while the vehicle is in motion. If the vehicle overheats or temp increases while the vehicle is stationary that is more likely an airflow issue as the fans may not be moving enough air through the radiator to remove heat from the coolant.
You noted fins being blocked. These are external to the tubes thru which the coolant flows. You can check if they are blocked by shining a light thru them. They can be cleaned with compressed air or sprayed with a garden hose but be careful not to bend or damage them.
If it is an original radiator the core can be replaced but it is not cheap. Basically more costly than a replacement radiator. Unless your car is rare or valuable you probably are better off buying a replacement. I would check timing and whether or not you have a fan shroud and whether or not you have a clutch fan that is working.
It is an original oem radiator the hoses are new the thermostat is 184 Degrees It is a new thermal driven fan with 5 blades there is a shroud also oem the cap is new has boiled over not sure on the temp. Took temp with heat gun Fan is half way in shroud. The car has air conditioning with the condenser coil in front of radiator. 50/50 coolant green. pump is working fine can see water moving from left to right looking in the radiator facing the engine. I was referring to the fin tubes inside the radiator I’m sure the radiator is original to car, scoped out the top which looked open but haven’t checked the bottom. No recirculation tank. Does not happen running in park.
Take a look at the size of the radiator hoses. Big aren’t they. They are that size because you have to move a massive amount of water to cool an engine that is dissipating about half its energy in the form of heat.
A really good old school radiator shop could flow test it for you but it is rare to find one. Most likely you need a new radiator.
One more thing to consider is that if engine hasn’t been rebuilt, there could be a ton of rusty sediment limiting coolant circulation. I couldn’t get my cooling problem fixed until I rodded out the block.
Hey, I had similar situation with my ‘67. Drove it around and constantly went hot after a few miles of street drive. I tried some of the things mentioned in this thread. Ended up being a bad guage. Start with basics then go simple. Best of luck.
I had this happen years ago in a 66 Mustang I had. The car ran fine around town but every time I got on the highway and got above 50 mph, it overheated. It had the original radiator and enough of the tubes had gotten plugged over the years it just couldn’t cool it enough when the engine was working and making more heat at the higher speeds.
Once the radiator was changed, it ran at the same temperature all the time again. You can sometimes get a good feel for the condition of the radiator if you take a hose and run it full force through it. It shouldn’t have any resistance with the water backing up and not moving easily through it.
I wouldn’t worry too much about a spring inside the radiator hose. As long as you have a radiator cap that has pressure when you go to open it on a working radiator you will notice that there is around 15 pounds of pressure when you open it. I’ve never had a radiator hose collapse.
Agree about the spring in the lower radiator hose. It was there to allow the factory to fill up with antifreeze under vacuum. The water pump doesn’t have enough suction to collapse a springless lower radiator hose in good condition.
You mention that the car is restored. Did you paint the radiator? If so, how heavily did you coat the fins? They should be only lightly dusted with paint. Excess paint thickness can severely compromise their ability to throw off heat. I have experienced this problem in the past.
If the automatic transmission fluid is low, more heat will be generated that the radiator will have to dissipate. Especially on the highway. Probably not your cause but every little bit pushed up the degrees.