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I've got 410 gears in my 67 with a 302 and C4. I have about a 45 minute drive to work on a road that I go about 55 mph on. When I get there (if not before I stop) I notice I'm losing coolant out of the overflow tube.The temp gauge doesn't work and the car doesn't have a tach (they will be ordered soon).

According to an online calculator, I should only be seeing about 3,300 RPM at 55 mph, so it seems odd that this would be occurring. Is it possible that I am overheating the coolant that much revving the engine at 3,300 for 45 min? Or is something else going on?
 

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Well,

Obviously you need to get your temp gauge fixed or at least buy one of those cheap non-contact temp meters so you can generate some data on what your coolant temperature is.

All the online calculators involving RPM, time, speed, etc. are about as useful as knowing your sign of the zodiac for diagnosing this issue, IF IT IS EVEN AN ISSUE.

By THAT I mean, if you add coolant to the top of the radiator cap every time you get home, then you WILL lose coolant every time you drive the car, assuming you don't have an overflow tank. That's kind of the reason they started using overflow tanks.

Bottom line, old mustangs can run hot and there are changes you can make to fix that, but without knowing:

1. Your coolant temperature and how it varies depending on if you are idling or driving on the highway:
2. The outside temperature during (1.) testing above.
3. What thermostat you are running.
4. Radiator condition
5. Type and status of fan clutch (if any)

I wouldn't know how to solve your issue...or if what your seeing could fall under the broad heading of "normal".

Phil
 
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First thing for you to do is either test your radiator cap or just replace it.
 

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Cold coolant level should be maximum 1" below the filler neck. Anything above that will just puke out, due to the coefficient of expansion of the hot coolant.
 
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