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Just to add another data point... the stock temp gauge in my wife’s 66 approaches the “P” in temp when I am blasting down the highway for long stretches in 90+ degree heat. It never goes higher, and that is the point the electric fan kicks on as well. I measured the actual temp using a digital meter and it was between 208F-210F. Not overheating by any means, just annoying to my OCD having the temp gauge needle move that much. 😛

My annoyance is I can’t figure out why it heats up at high speeds like that. It actually runs cooler putting around town than it does at 70mph... my guess is air isn’t going through the radiator like it should. These cars have wacky aerodynamic features, but they look cool!
 

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Just to add another data point... the stock temp gauge in my wife’s 66 approaches the “P” in temp when I am blasting down the highway for long stretches in 90+ degree heat. It never goes higher, and that is the point the electric fan kicks on as well. I measured the actual temp using a digital meter and it was between 208F-210F. Not overheating by any means, just annoying to my OCD having the temp gauge needle move that much. 😛

My annoyance is I can’t figure out why it heats up at high speeds like that. It actually runs cooler putting around town than it does at 70mph... my guess is air isn’t going through the radiator like it should. These cars have wacky aerodynamic features, but they look cool!

Had a similar problem of running hot on interstate, but cooler in city traffic. Replaced radiator, and it solved my problem. Tubes in new radiator were larger. Old radiator appeared "good" when running water through it with a hose, but likely was partially blocked with crud.
 

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Had a similar problem of running hot on interstate, but cooler in city traffic. Replaced radiator, and it solved my problem. Tubes in new radiator were larger. Old radiator appeared "good" when running water through it with a hose, but likely was partially blocked with crud.
Everything in the cooling system is new (well, less than a year old at this point), including the 2 core aluminum radiator. It’s a 200 straight six engine with a C4 and 3.20 rear end, so it’s spinning at 3000+rpm going 70mph... not sure if that’s part of the issue.

I’ve read about collapsing coolant hoses, but I’m not sure how to check for that blasting down the highway. Whenever I check the radiator hoses they are good and firm. 🤷‍♂️ My thought is that there is a series of events that causes the lower hose (water pump suction) to collapse that I can’t repeat in the driveway or there is a weird airflow problem at higher speeds.

Sorry to thread jack, but if anyone has other ideas I am all ears.
 

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The reproduction temp senders are way off from a stock Ford temp sender. Often people replace the good working unit with a crappy Scott Drake repop for no apparent reason. Look here:Faulty Repop Temp Senders
 

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Everything in the cooling system is new (well, less than a year old at this point), including the 2 core aluminum radiator. It’s a 200 straight six engine with a C4 and 3.20 rear end, so it’s spinning at 3000+rpm going 70mph... not sure if that’s part of the issue.

I’ve read about collapsing coolant hoses, but I’m not sure how to check for that blasting down the highway. Whenever I check the radiator hoses they are good and firm. 🤷‍♂️ My thought is that there is a series of events that causes the lower hose (water pump suction) to collapse that I can’t repeat in the driveway or there is a weird airflow problem at higher speeds.

Sorry to thread jack, but if anyone has other ideas I am all ears.
Load-O-Matic or dual-advance distributor? When was the last time the advance curve was checked/calibrated?
 

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Discussion Starter #26
Everything in the cooling system is new (well, less than a year old at this point), including the 2 core aluminum radiator. It’s a 200 straight six engine with a C4 and 3.20 rear end, so it’s spinning at 3000+rpm going 70mph... not sure if that’s part of the issue.

I’ve read about collapsing coolant hoses, but I’m not sure how to check for that blasting down the highway. Whenever I check the radiator hoses they are good and firm. 🤷‍♂️ My thought is that there is a series of events that causes the lower hose (water pump suction) to collapse that I can’t repeat in the driveway or there is a weird airflow problem at higher speeds.

Sorry to thread jack, but if anyone has other ideas I am all ears.
Squeeze your lower radiator hose when the engine is cool and feel for the spring inside. If no spring, then assume worst case that it is collapsing. If you have a spring, I think it is safe to assume that it is NOT collapsing.

You're in the same boat as me. Hotter on the interstate than scooting around a 50mph, new 2-core aluminum radiator. I've been told that it is POSSIBLE that the "outflow" side of my cooling system is too good. The theory is that coolant gets hot in the block, then flows quickly through the more efficient new, 2-core, aluminum radiator (that has larger tubes than brass radiators.) The coolant lacks sufficient dwell time in the radiator to give up its heat and goes back into the block warmer than desired. Then it picks up more heat from the block and fails to exchange it again until reaching equilibrium...which is hotter than we'd like.

Ironically, the solution I was told would be to restrict the lower radiator hose, so that coolant had longer time in the radiator...which is exactly what a collapsed hose would be doing...causing HIGH heat! Maybe there's a coolant flow / thermal flow sweet spot, I don't know. Regardless, I'm too old and too poor to attempt this science experiment to figure it out properly. I'll stick with P=210 in my case!
 

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One thing that some may consider when they are installing a water pump, is that the port match is very poor. Matching the ports may help water flow significantly. I had to port match just the water pump on my 331...didn't have to touch the block.
 
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