Okay guys. Fairly straight forward question, hopefully some straight forward answers.

67 SS 490 BBC Completely frshened up
AFCO Aluminum Racing Radiator (7 Lb cap)
Flex-a-lite Dual Electric fans

I installed the motor this past week. Started up on first try, almost dead on. Made a few adjustments, including rollers, all went well.

Brought the car home from the shop today, and about half way there, I saw my console temp guage start to climb around half way. Then, I turned the corner to my home and the guage needle pegged and buried ALL the way to HOT side. This was about 4 houses down road.

So I pulled it in the driveway, shut her down, and coolant was boiling over from the canister.

So i have a few questions:
1. What could of caused this?
2. What temp does that mean it went to?
3. What should I be checking for 1st?
4. Why me? (just kidding)

Thanks ahead of time.

Are you running a thermostat? -- if so, make sure it isn't stuck closed

7# cap? You probably exceeded the cap rating. Once the cap relieves, it's like a geyser, all the water flash boils and you have no coolant left. Put a 20# cap on your radiator.
What kind of water pump and how is it driven?

If it pegged...it's close to boiling I think. If you don' t need a thermostat heave it. Or pop out the element and leave the rest so you have better water flow....that way water will stay in the radiator long enough... to get cooled. Do you have an electric fan also?

Oh yea...Why you? Cause you have the guts to run a big block. Congrats.

Or pop out the element and leave the rest so you have better water flow....that way water will stay in the radiator long enough... to get cooled. Do you have an electric fan also?

Does higher flow mean the water stays in the radiator longer? How does cool water affect the efficiency of the radiator?

The answer is no on higher flow staying in radiator longer. What I mean is if you take the thermostat out the water may flow too fast and not stay in the radiator long enough. Just had that happen, so what I did was punch out the middle of the thermostat so you have constant flow but the hole is more narrow than when the entire thermostat is out. I took the spring element out. It worked for me. I'm in Florida and we have very little need for thermostats. Not cold enough in winter and always hot in the summer. What do you mean by your second question? The radiator is the cooling spot for the water.

Well, my initial thought was that there was air in the system from being freshly installed and filled. So today I had a chance to look and did a few things.

1- I filled the radiator back up
2- I tested the thermostat, and it works fine
3- I ran the motor without the stat in to make sure coolant was flowing in radiator, it was
4- I reinstalled stat, ran motor for a few, with cap off, and saw no major change in temp, although I didn't run for very long

Raining like crazy today, so I can't give her a drive.

I will let you know what happens when I drive it a little.

When the temp shoots up that fast it's an air bubble. I bet you have it whipped.

The answer is no on higher flow staying in radiator longer. What I mean is if you take the thermostat out the water may flow too fast and not stay in the radiator long enough. Just had that happen, so what I did was punch out the middle of the thermostat so you have constant flow but the hole is more narrow than when the entire thermostat is out. I took the spring element out. It worked for me. I'm in Florida and we have very little need for thermostats. Not cold enough in winter and always hot in the summer. What do you mean by your second question? The radiator is the cooling spot for the water.

Why does the water need to stay in the radiator for any extended length of time? The radiator just exchanges heat at a rate based on the difference in temperature of the radiator and the cooling air. If the water in the radiator isn't hot the rate of heat exchange goes down, which will lead to higher engine temperatures. Slowing the flow and letting the water cool in the radiator reduces the efficiency of the cooling system.

Why does the water need to stay in the radiator for any extended length of time? The radiator just exchanges heat at a rate based on the difference in temperature of the radiator and the cooling air. If the water in the radiator isn't hot the rate of heat exchange goes down, which will lead to higher engine temperatures. Slowing the flow and letting the water cool in the radiator reduces the efficiency of the cooling system.

The more coolant flow or airflow the higher efficiency of the system period. The "slowing the flow" mentality is physic's challanged and/or simply misinformed.

Check out the links in my signature line.

Since the thermostat regulates flow....All I was saying was that if you don't run a thermostat maybe the flow is too fast to cool. I mentioned what worked for me. I'll leave the physics to you guys. Good luck man.

Since the thermostat regulates flow....All I was saying was that if you don't run a thermostat maybe the flow is too fast to cool. I mentioned what worked for me. I'll leave the physics to you guys. Good luck man.

The thermostat regulates flow by increasing the flow when the engine is warm, which leads to more heat being exchanged and the engine cooling down. When the engine cools down, the thermostat closes down to decrease the flow and keep the engine warm.

I think onova was onto it in his 1st post, why are you running a 7lb rad cap? Is it required for your overflow to work? The boiling point of water goes up under pressure and most cooling systems typically run a 15lb or 16lb cap...

The 7# cap is the billet one....