[panhead59]

'66 gto 455 c.i. 6x heads. tripower, Lunati voodoo 704 cam. New alum radiator since old one stated to leak. New fan clutch and new 180 thermostat. Stock shroud in place. As soon as the temp comes up a little, water rises out of radiator. Put cap on, temp gauge normal. 180-200. Water seems to overflow into catch tank after awhile. Boiling also. But temp gauge seems normal. Temp fine at highway speeds but stop and it rises quickly, into 220 range. Something is obviously wrong here. Seems like a blockage to me since water rises out of radiator. Thoughts? Bad, new thermostat?

[chrisp]

Get the air out & refill to 2" below the neck .

[Blued and Painted]

Check for combustion gasses in the cooling system. This can be done with a CO sniffer, emission machine. Dont get probe into coolant. There is also a chemical head gasket checker.
-- https://www.amazon.com/UVIEW-560000-...et+leak+tester --
Most parts stores carry a similar kit.

If there is carbon monoxide in cooling system, possible causes could be
cracked cylinder head
head gasket not sealing
aftermarket head bolts to long.
head or block surface needs milling

[Chris65LeMans]

You've got a couple different things going on there. First - you'll need an infrared thermometer to double check and make sure your temp gauge is giving you the right numbers.

If your temp checks out, then your coolant boiling at 200 degrees needs attention. My guess is a bad radiator cap. (It's not pressurizing your cooling system correctly, and allowing it it boil at lower temps.)

Water flowing into the overflow tank as the coolant heats up is normal- that's how it works.

[panhead59]

What's wrong with the strips u put in the coolant? I work for a very large trucking co. and that's what they use. Maybe ok for diesel engines. Just wondering. I will get a infrared thermometer. What's the best way to get the air out? I thought just by leaving the cap off for a few minutes did the trick. Guess not.

[GT182]

I had a 13# cap and went to q 16#. Sure helped to keep the Goat from marking it's territory every place I'd stop. LOL

Panhead59, don't run any less than a 50-50 mix of antifreeze.

[panhead59]

So will 2 gal. of anti freeze be enough to obtain the 50/50 mix? Or what is the total for engine and radiator? Or just go by temp. protection setting on anti freeze tester? TKS

[panhead59]

Oh by the way. Auto zone will rent you the tester for the CO sniffer. $25. Then u get your money back when you return it, so it's like a loaner program. All you have to buy is the $10 liquid testing fluid. If it turns yellow, you've got contamination. Advance auto didn't have the tester at all.

[GT182]

Find gallon jugs of 50/50 mix if you can. PepBoys , Auto Zone, or Napa should carry it. That way there's no worry on water to antifreeze mix. Capacity is 20 quarts with the heater for the 389/421 system. Not sure on a 455 in a 66. My Chilton's say 17.5 to 23.1 depending on the year and radiator.