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Overheating Issues '66 Coronet 500 with 361/4-Barrel

j57little

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I have owned four Coronets in my lifetime; a 66, 67, 68 and 71, with engines from 318 to 440. Overheating was always something to watch for, especially on the BB's and RB's.

I currently have a 66 Coronet/361 with a 22-inch radiator and stock fan with about a 1.5 inch extension (no shroud on this 66). The car overheats at low speed and high speed. I tried a new thermostat and not only did it still overheat, the old return hose blew. I replaced the hoses (upper and lower - with spring) and replaced the water pump. No more leaks, but same overheating problem. After 20 miles I am making lots of steam - the 50/50 water and anti-freeze type.

I tried an aftermarket aluminum 2 core radiator with dual 10" fans and shroud pulling air in at about 5400 cfm. The aluminum radiators are supposed to be more efficient than original brass and the air flow should be more than adequate, but it still overheats! My 361 does have a four barrel aftermarket carb, but when the only thing left is figuring that I might have a lean fuel mixture, well, things are bad at that point. It's not like I am saving any fuel by running lean - it definitely suffers on gas mileage. I am running about 97 octane, but I wouldn't think that's an issue.

I am thinking about removing the thermostat entirely. And I am thinking that a 22 inch radiator was probably barely adequate for a 361, but when I add a four barrel and make more power, I also make more heat and I might be overtaxing the 22-inch. I may need a 26 inch, but then the front wall will block two inches of the radiator on each side, so I gain only fluid quantity.

Any thoughts are appreciated!!!!
 
Things I have done to my Coronet this past summer, in order:

1) Completely drained and flushed the coolant system. Rust inside the block hinders heat transfer
2) Installed a 26" aluminum rad with a 7-blade 18" fan, no clutch. New hoses, 16 psi cap
3) Installed a MP fan shroud
4) Sacrificial anode cap
5) Installed a "215" 7-blade fan with HD clutch

The final issue I had was the temp needle creeping up when idling/sitting still but after upgrading to the 215 it's better.

Removing the thermostat will reduce the residence time of coolant in the rad and might not help much. 5400 cfm sounds like a lot of air and I'm surprised that would not cool it! Also remember the hood-to-rad weatherstrip/seal is supposed to help but I'm managing without one ($45 from Summit, I put the money into the clutch).

If its air/fuel related then there are ways of diagnosing that issue.
 
I run a 383 BB with 10:1 CR through a 22" rad with a 180 degree full flow stat and a 16 lb. rad cap and the engine runs between 180 - 185 all day. In your case, you're either making too much heat for the size of the cooling system or the cooling system will not dissipate the heat properly. Here is a list of things that cause these problems:

Timing retarded too much
Poor lubrication within the engine itself ( possibly lower than normal oil pressure or wrong grade of oil)
Scaled walls of the cooling jackets in the engine
Combustion gases sneaking by the head gaskets ( when it's bad, white smoke out the tailpipe)
Minor crack in the engine block or heads ( same as above)
Wrong impeller on the water pump or wrong rotation ( Ford 289's had CW and CCW pumps - never trust rebuilders)
Wrong T-stat and/or wrong rad cap ( higher pressure = higher boiling point )
Cavitation in the water pump or air in the cooling system ( return overflow tanks are a must )
Severely cramped engine compartments with little to no air circulation
Missing fan shrouds, pusher electric fans, debris in rad fins etc. ( poor air flow through the rad )
Serious engine drag (caused by poorly adjusted brakes or brakes dragging)
Slipping belts and/or wrong sized pulleys.
Contaminated, poorly mixed coolant.
Clutch on fan not engaging properly

Now we know when Chrysler made this car it would never had sold with this kind of problem so over the years things have changed and probably not for the better. Unfortunately getting it back to it's original state could get somewhat expensive so I would start with the simplest, easiest and least expensive checks first. Pressure test the cooling system and monitor the oil pressure. Set the timing ( check for a slipped balancer ) to factory spec, belt tension, rad cap and a decent thermostat. You get the gist. Good luck because cooling issues can be a bear to resolve, sometimes.
 
But other than that, what could possibly go wrong? Actually, I suspect up to half of the items you listed could be factors. I'll check the timing, servicing, air - the simple items, but if it is a corroded/cracked engine block (the car basically sat for the better part of 30 years) it could be a lesson in futility here. Fortunately I've seen very little exhaust smoke, so I am hoping the serious issues are not in play. Thank you so much for the great advice!!!!
 
Try it without a thermostat. Will it cool at idle? Or does it slowly creep up in temp?

- - - Updated - - -

Do you have an accurate temp gauge? Did you properly purge all the air out of the system?
 
I'm having the exact same thing with my 68 charger 383 except at idle it doesn't overheat but when I drove it for the 1st time a week ago apps 20 miles it ran hot. i recently had the engine rebuilt with some hi po upgrades and it ran perfect on their Dyno.
 
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